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Effect of cam-type femoroacetabular impingement on hip joint kinematics Given, Laura Elizabeth 2010

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EFFECT OF CAM-TYPE FEMOROACETABULAR IMPINGEMENT ON HIP JOINT KINEMATICS  by  Laura Elizabeth Given BASc, University of Waterloo, 2007  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in  THE FACULTY OF GRADUATE STUDIES (MECHANICAL ENGINEERING) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) June, 2010  ©Laura Elizabeth Given, 2010  Abstract Cam-type femoroacetabular impingement is a painful disorder common in young adults, caused by decreased concavity of the femoral head-neck. It is associated with hip osteoarthritis, though the exact mechanism of joint damage is not fully understood. Gait analysis has shown that cam deformities cause changes to coupled motions in vivo, though it is unclear whether these changes are compensatory or due to direct bony contact. The objective of this study was to determine how cam deformities and surgical resection affect patterns of hip rotation, translation of the center of rotation, and force required to flex and abduct the hip. We assessed the relationship between deformity and coupled motions, translations of center of femoral rotation, and force required to create active unconstrained flexion and abduction ex vivo. Three deformities were simulated on each of six hemi-pelvis/proximal femur specimens. Four muscles were simulated by cables drawn from the distal tendon to the location of proximal attachment. Motion was created by actively shortening one of these cables while statically loading the others. Markers on the femur and pelvis were tracked, allowing for calculation of joint rotations and translations. A load cell on the active cable allowed for measurement of the applied force. We found that deformity resulted in increased external rotation, adduction and translation during flexion and increased internal rotation, extension and decreased translation during abduction. We also found that when a more severe deformity was present, more force was required to create both flexion and abduction to the same angle. Further, we found that resection resulted in increased internal rotation and translation during flexion and decreased internal rotation during abduction. Less force was required to create flexion and abduction following resection. ii  Changes to motion patterns occur as a result of changed contact loads between the femoral head and acetabulum, resulting in loading of regions of articular cartilage which may not be optimized for these loads and may, therefore, begin a degenerative cascade leading to osteoarthritis.  As coupled motions were observed within ranges of flexion and abduction  required for daily living, it is recommended that resection be performed in an attempt to slow the progression of osteoarthritis by limiting contact between the femoral head-neck and acetabulum.  iii  Table of Contents Abstract ........................................................................................................................................... ii Table of Contents ........................................................................................................................... iv List of Tables ................................................................................................................................ vii List of Figures ................................................................................................................................ ix List of Abbreviations ................................................................................................................... xvi Acknowledgements .................................................................................................................... xviii Co-Authorship Statement............................................................................................................. xix 1  Introduction and Literature Review ........................................................................................ 1 1.1  Introduction ............................................................................................................... 1  1.2  The hip joint - anatomy ............................................................................................. 1  1.3  Osteoarthritis (OA) of the hip ................................................................................... 5  1.4  Femoroacetabular impingement (FAI) ..................................................................... 7  1.4.1  Introduction to FAI ............................................................................................ 7  1.4.2  Etiology and epidemiology of cam FAI ............................................................ 8  1.4.3  Diagnosis and quantification of cam FAI .......................................................... 9  1.4.4  Cam FAI and joint damage .............................................................................. 16  1.4.4.1 Cam FAI and labral tears .................................................................................... 16 1.4.4.2 Cam FAI and OA of the hip ................................................................................ 17 1.4.5  The causal relationship between cam FAI and hip OA ................................... 18  1.4.6  The mechanism of joint damage in cam FAI .................................................. 20  1.4.7  Treatment of cam FAI ..................................................................................... 22  1.5  Hip kinematics ........................................................................................................ 25  1.5.1  Anatomical coordinate systems ....................................................................... 25  1.5.2  Center of the hip .............................................................................................. 29  1.5.3  Translational motions of the hip joint.............................................................. 31  1.5.4  Rotational motions of the hip joint .................................................................. 33  1.5.4.1 In vivo measurements of rotational kinematics................................................... 33 1.5.4.2 Ex vivo measurements of rotational kinematics ................................................. 37 1.5.4.3 In vitro measurements of rotational kinematics .................................................. 38 iv  1.5.4.4 Computer simulations of rotational kinematics .................................................. 38 1.6  2  Hip loading.............................................................................................................. 41  1.6.1  Mechanical methods ........................................................................................ 41  1.6.2  Imaging methods ............................................................................................. 42  1.6.3  Models and simulations ................................................................................... 43  1.7  Summary and directions ......................................................................................... 44  1.8  References ............................................................................................................... 46  Effect of Cam FAI on Hip Joint Kinematics ........................................................................ 58 2.1  Introduction ............................................................................................................. 58  2.2  Materials and methods ............................................................................................ 60  2.2.1  Specimen preparation ...................................................................................... 60  2.2.2  Deformity simulation ....................................................................................... 60  2.2.3  Dynamic hip motion simulator (DHMS) ......................................................... 61  2.2.4  Experimental procedures ................................................................................. 63  2.2.5  Kinematic procedures ...................................................................................... 64  2.2.6  Imaging and morphological measurements ..................................................... 65  2.2.7  Sources of funding ........................................................................................... 66  2.3  Statistical methods .................................................................................................. 66  2.4  Results ..................................................................................................................... 67  2.4.1  Accuracy and repeatability of the DHMS ....................................................... 67  2.4.2  Changes in kinematics due to deformity severity ............................................ 67  2.4.2.1 Prescribed flexion................................................................................................ 67 2.4.2.2 Prescribed abduction ........................................................................................... 76 2.4.3  3  Changes in kinematics due to resection osteochondroplasty........................... 84  2.5  Discussion ............................................................................................................... 94  2.6  References ............................................................................................................. 100  Integrated Discussion .......................................................................................................... 102 3.1  Motivation and findings ........................................................................................ 102  3.1.1  Coupled motions ............................................................................................ 102  3.1.2  Translations ................................................................................................... 105  3.1.3  Force requirements ........................................................................................ 106 v  3.1.4 3.2  Resection osteochondroplasty ....................................................................... 108 Significance of findings ........................................................................................ 108  3.2.1  Significance of coupled motions ................................................................... 108  3.2.2  Significance of translations ........................................................................... 109  3.2.3  Significance of force requirement ................................................................. 110  3.2.4  Mechanism of joint damage .......................................................................... 110  3.2.5  Clinical significance ...................................................................................... 111  3.3  Study strengths and limitations ............................................................................. 112  3.3.1  Study strengths .............................................................................................. 112  3.3.2  Study limitations ............................................................................................ 112  3.4  Future directions ................................................................................................... 115  3.5  Conclusions ........................................................................................................... 118  3.6  References ............................................................................................................. 120  Appendix A: Ethics ..................................................................................................................... 121 Appendix B: Muscles that Cross the Hip Joint ........................................................................... 124 B.1  Tables of muscles .................................................................................................. 125  B.2  References ............................................................................................................. 129  Appendix C: Dynamic Hip Motion Simulator ............................................................................ 130 C.1  DHMS frame ......................................................................................................... 131  C.2  Motion ................................................................................................................... 132  Appendix D: Quantification of Sources of Error ........................................................................ 134 D.1  Marker tracking error ............................................................................................ 135  D.2  Marker motion error .............................................................................................. 135  D.3  System origin error ............................................................................................... 136  D.4  System axes error .................................................................................................. 137  D.5  Total translation error ........................................................................................... 137  D.6  Total angle error .................................................................................................... 139  D.7  Deformity quantification error .............................................................................. 139  D.8  Repeatability of motion......................................................................................... 139  Appendix E: Additional Results ................................................................................................. 141 Appendix F: Deformity Measurements ...................................................................................... 170 vi  List of Tables Table 1-1: Clinical outcomes of surgical treatment of FAI syndrome. .........................................23 Table 1-2: Recent clinical outcomes of surgical treatment of FAI syndrome. ..............................24 Table 2-1: Changes in intercept and slope for the mean profiles of internal rotation, abduction and force during prescribed flexion due to deformity severity. Coefficients, p-values and confidence intervals provided. ...................................................71 Table 2-2: Changes in intercept and slope for the direction of translation for the mean profiles during prescribed flexion due to deformity severity. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially. .............................................................................................................75 Table 2-3: Change in intercept and slope in the mean profiles during prescribed abduction due to deformity severity. Coefficients, p-values and confidence intervals provided. .......79 Table 2-4: Changes in intercept and slope for the direction of translation for the mean profiles during prescribed abduction due to deformity severity. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially. .............................................................................................................82 Table 2-5: Changes in intercept and slope for the mean profiles during prescribed flexion due to resection. Coefficients, p-values and confidence intervals provided. ......................86 Table 2-6: Changes in intercept and slope of the direction of translation for the mean profiles during prescribed flexion due to resection.  Coefficients, p-values and  confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially. ...............................................................................................................................88 vii  Table 2-7: Changes in intercept and slope for the mean profiles during abduction due to resection. Coefficients, p-values and confidence intervals provided. .................................91 Table 2-8: Changes in intercept and slope of the direction of translation for the mean profiles during prescribed abduction due to resection. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially. ...............................................................................................................................93 Table B-1: Flexor muscles. ..........................................................................................................125 Table B-2: Extensor muscles. ......................................................................................................126 Table B-3: Abductor muscles. .....................................................................................................127 Table B-4: Adductor muscles. .....................................................................................................127 Table B-5: Lateral rotator muscles. .............................................................................................128 Table B-6: Medial rotator muscles. .............................................................................................129 Table D-1: Summary of maximum change in distance between any two markers. ....................135 Table D-2: Summary of the maximum transformation error. ......................................................136 Table D-3: Summary of repeatability in determining system axes..............................................137 Table F-1: Summary of alpha angle measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given. ....171 Table F-2: Summary of triangular index measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given................................................................................................................................172 Table F-3: Summary of offset ratio measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given. ....173  viii  List of Figures Figure 1-1: A) Lateral view of a left hemi-pelvis. B) Right proximal femur. [59] .........................2 Figure 1-2: A) Anterior view of pelvis. B) Posterior view of pelvis. [59] ......................................3 Figure 1-3: Lateral view of the acetabulum. The labrum is continuous with the articular cartilage. The transverse acetabular ligament closes the acetabular notch. ..........................4 Figure 1-4: Osteoarthritic hip joint. .................................................................................................6 Figure 1-5: A) Cam FAI caused by nonspherical femoral head abutting against the rim of the acetabulum. B) Pincer-type FAI caused by overcoverage of the femoral head. ..............8 Figure 1-6: The passive impingement test. The patient lies supine while the examining physician flexes the thigh to 90°, then adducts and internally rotates the leg. If the patient experiences pain, the test is positive. ........................................................................10 Figure 1-7: Offset ratio measurement. ORi is the offset ratio for interval i, FHI is the femoral head radius for interval i, Oi is the neck radius for interval i and R is the radius of the circle of best fit of the femoral head. ...............................................................11 Figure 1-8: Alpha angle measurement. A) Normal hip joint B) Hip with cam FAI. .....................12 Figure 1-9: Alpha angle differences between cam and pincer FAI in eight positions. ..................14 Figure 1-10: Triangular index. r is the radius of the femoral head, B is the line through the center of the femoral neck, H is the height at 1/2r along B and R is the pathological radius. ...................................................................................................................................16 Figure 1-11: Distribution of labral and chondral damage sites......................................................20 Figure 1-12: Illustration of the mechanism of joint damage in cam FAI. .....................................21 Figure 1-13: Hip joint coordinate systems. ....................................................................................26 Figure 1-14: Cardan angle coordinate system rotations. The first rotation, α, is about the Zaxis (red), the second rotation, β, is about the new X-axis (blue) and the third rotation, γ, is about the new Y-axis (purple). .......................................................................27  ix  Figure 1-15: Helical axis representation of rotations and translations. Motion is represented as a combined rotation about and translation along a single axis (d). ..................................28 Figure 1-16: Rotations and translations of the hip joint during passive flexion. ...........................32 Figure 1-17: Mean (+/- standard deviation) frontal hip angles of FAI and control groups during level gait. ...................................................................................................................35 Figure 1-18: Mean (+/- standard deviation) sagittal hip angles of the FAI and control groups during level gait. .......................................................................................................35 Figure 1-19: Mean (+/- standard deviation) frontal pelvic anlges of the FAI and control groups during level gait. .......................................................................................................36 Figure 1-20: Mean (+/- standard deviation) pelvic tilt of FAI and control groups. .......................37 Figure 1-21: Simulation of hip joint ranges of motion. A) Full flexion. B) Full abduction. C) Full adduction. .................................................................................................................39 Figure 2-1: A) Hemi-pelvis specimen with open joint capsule and no simulated deformity. B) Same specimen with simulated deformity (arrow). .........................................................61 Figure 2-2: Loading schematic. Red lines represent cables, blue dots represent eyebolts. The eyebolt associated with the gluteus maximus is hidden by the iliac wing in this view. .....................................................................................................................................62 Figure 2-3: Raw motion data for internal rotation as a function of prescribed flexion in all flexion trials for one specimen. ............................................................................................68 Figure 2-4: Mean profile for internal rotation of the femur during prescribed flexion. ................69 Figure 2-5: Mean profile for abduction of the femur during prescribed flexion. ..........................69 Figure 2-6: Mean profile for the force required to create prescribed flexion. ...............................70 Figure 2-7: Mean profile for Euclidean translation of the COR of the femur during prescribed flexion. ................................................................................................................72 Figure 2-8: Mean profile for translation of the COR of the femur along the X-axis during prescribed flexion. Translation in the positive X-direction corresponds to translation in the anterior direction. .......................................................................................................73 x  Figure 2-9: Mean profile for translation of the COR of the femur along the Y-axis during prescribed flexion. Translation in the positive Y-direction corresponds to translation in the proximal direction. .....................................................................................................73 Figure 2-10: Mean profile for translation of the COR of the femur along the Z-axis during prescribed flexion. Translation in the positive Z-direction corresponds to translation in the lateral direction. ..........................................................................................................74 Figure 2-11: Mean profile for internal rotation of the femur during prescribed abduction. ..........77 Figure 2-12: Mean profile for flexion of the femur during prescribed abduction. ........................77 Figure 2-13: Mean profile for the force required to create prescribed abduction. .........................78 Figure 2-14: Mean profile for Euclidean translation of the COR of the femur during prescribed abduction. ............................................................................................................80 Figure 2-15: Mean profile for translation of the COR of the femur along the X-axis during prescribed abduction.  Translation in the positive X-direction corresponds to  translation in the anterior direction.......................................................................................81 Figure 2-16: Mean profile for translation of the COR of the femur along the Y-axis during prescribed abduction.  Translation in the positive Y-direction corresponds to  translation in the proximal direction.....................................................................................81 Figure 2-17: Mean profile for translation of the COR of the femur along the Z-axis during prescribed abduction.  Translation in the positive Z-direction corresponds to  translation in the lateral direction. ........................................................................................82 Figure 2-18: Mean profile for internal rotation of the femur during prescribed flexion comparison of the native and resected conditions. ...............................................................84 Figure 2-19: Mean profile for abduction of the femur during prescribed flexion comparison of the native and resected conditions. ...............................................................85 Figure 2-20: Mean profile for the force required to create prescribed flexion - comparison of the native and resected conditions....................................................................................85 Figure 2-21: Mean profile for Euclidean translation of the COR of the femur during prescribed flexion - comparison of native and resected conditions .....................................86 xi  Figure 2-22: Mean profile for translation of the COR of the femur along the X-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive X-direction corresponds to translation in the anterior direction. ............................87 Figure 2-23: Mean profile for translation of the COR of the femur along the Y-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive Y-direction corresponds to translation in the proximal direction. ..........................87 Figure 2-24: Mean profile for translation of the COR of the femur along the Z-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive Z-direction corresponds to translation in the lateral direction. ...............................88 Figure 2-25: Mean profile for internal rotation of the femur during prescribed abduction comparison of the native and resected conditions. ...............................................................89 Figure 2-26: Mean profile for flexion of the femur during prescribed abduction comparison of the native and resected conditions. ...............................................................90 Figure 2-27: Mean profile for force required to create prescribed abduction - comparison of the native and resected conditions. .......................................................................................90 Figure 2-28: Mean profile for Euclidean translation of the COR of the femur during prescribed abduction - comparison of the native and resected conditions. ..........................91 Figure 2-29: Mean profile for translation of the COR of the femur along the X-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive X-direction corresponds to translation in the anterior direction. ......................92 Figure 2-30: Mean profile for translation of the COR of the femur along the Y-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive Y-direction corresponds to translation in the proximal direction. ....................92 Figure 2-31: Mean profile for translation of the COR of the femur along the Z-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive Z-direction corresponds to translation in the lateral direction. .........................93  xii  Figure 3-1: Pelvic anatomy. Black arrow indicates lip on superior region of acetabulum which would apply an anterior force to the cam deformity during abduction, rotating the femur internally. [3] ......................................................................................................104 Figure C-1: Dynamic Hip Motion Simulator (DHMS). A) Locking wheels. B) Horizontal sliding pulley bars which lock into place. C) Vertical sliding specimen attachment bar. D) Rotating specimen attachment plate. E) Angle adjustment for specimen attachment bar. F) Vertical posts for pulleys, adjustable in height and angle and along the pulley bars (B). G) Pulleys. ..............................................................................131 Figure C-2: Schematic of the motion control system. Custom Labview™ code controlled the DAQ output which went through a current amplifier to the motors which shortened the cables, creating motion. Feedback was provided through load cells in line with the cables. ............................................................................................................133 Figure E-1: Internal rotation angles during prescribed flexion for each individual specimen. ...142 Figure E-2: Abduction angles during prescribed flexion for each individual specimen. ............143 Figure E-3: Euclidean translation of the COR of the femur during prescribed flexion for each individual specimen. ..................................................................................................144 Figure E-4: Translation of the COR of the femur along the X-axis during prescribed flexion.  Positive translation along the X-axis corresponds to translation in the  anterior direction. ...............................................................................................................145 Figure E-5: Translation of the COR of the femur along the Y-axis during prescribed flexion.  Positive translation along the Y-axis corresponds to translation in the  proximal direction. .............................................................................................................146 Figure E-6: Translation of the COR of the femur along the Z-axis during prescribed flexion. Positive translation along the Z-axis corresponds to translation in the lateral direction. .............................................................................................................................147 Figure E-7: Force required to create prescribed flexion for each individual specimen. ..............148 Figure E-8: Internal rotation angles during prescribed abduction for each individual specimen. ............................................................................................................................149 xiii  Figure E-9: Flexion angles during prescribed abduction for each individual specimen..............150 Figure E-10: Euclidean translation of the COR of the femur during prescribed abduction for each individual specimen. ..................................................................................................151 Figure E-11: Translation of the COR of the femur along the X-axis during prescribed abduction. Positive translation along the X-axis corresponds to translation in the anterior direction. ...............................................................................................................152 Figure E-12: Translation of the COR of the femur along the Y-axis during prescribed abduction. Positive translation along the Y-axis corresponds to translation in the proximal direction. .............................................................................................................153 Figure E-13: Translation of the COR of the femur along the Z-axis during prescribed abduction. Positive translation along the Z-axis corresponds to translation in the lateral direction. ..................................................................................................................154 Figure E-14: Force required to create prescribed abduction for each individual specimen. .......155 Figure E-15: Internal rotation angles during prescribed flexion for each individual specimen, comparison of native and resected conditions. ..................................................156 Figure E-16: Abduction angles during prescribed flexion for each individual specimen, comparison of native and resected conditions. ...................................................................157 Figure E-17: Euclidean translation of the COR of the femur during prescribed flexion for each individual specimen, comparison of native and resected conditions. ........................158 Figure E-18: Translation of the COR of the femur along the X-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the X-axis corresponds to translation in the anterior direction. ...............................................159 Figure E-19: Translation of the COR of the femur along the Y-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the Y-axis corresponds to translation in the proximal direction. .............................................160 Figure E-20: Translation of the COR of the femur along the Z-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the Z-axis corresponds to translation in the lateral direction. ..................................................161 xiv  Figure E-21: Force required to create prescribed flexion for each individual specimen, comparison of native and resected conditions. ...................................................................162 Figure E-22: Internal rotation during prescribed abduction for each individual specimen, comparison of native and resected conditions. ...................................................................163 Figure E-23: Flexion angles during prescribed abduction for each individual specimen, comparison of native and resected conditions. ...................................................................164 Figure E-24: Euclidean translation of the COR of the femur during prescribed abduction for each individual specimen, comparison of native and resected conditions. ........................165 Figure E-25: Translation of the COR of the femur along the X-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the X-axis corresponds to translation in the anterior direction...........................................166 Figure E-26: Translation of the COR of the femur along the Y-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the Y-axis corresponds to translation in the proximal direction.........................................167 Figure E-27: Translation of the COR of the femur along the Z-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the Z-axis corresponds to translation in the lateral direction. ............................................168 Figure E-28: Force required to create prescribed abduction for each individual specimen, comparison of native and resected conditions. ...................................................................169  xv  List of Abbreviations  2D – Two dimensional 3D – Three dimensional AP – Anterior posterior AVN – Avascular necrosis ASIS – Anterior superior iliac spine CAN – Canadian Arthritis Network COR – Center of rotation CT – Computed tomography dGEMRIC – Delayed gandolinium enhanced magnetic resonance imaging contrast DHMS – Dynamic hip motion simulator EMG – Electromyography FAI – Femoroacetabular impingement FE – Femoral epicondyle FEM – Finite element modeling MR – Magnetic resonance MRI – Magnetic resonance imaging MSFHR – Michael Smith Foundation for Health Research NSAIDs – Non-steroidal anti-inflammatory drugs NSERC – National Science and Engineering Research Council of Canada OA – Osteoarthritis PCSA – Physiological cross-sectional area  xvi  PMMA – Polymethyl-methacrylate PSIS – Posterior superior iliac spine qMRI – Quantatative magnetic resonance imaging ROM – Range of motion RSA – Roentgen stereophotogrammetric analysis SCFE – Slipped capital femoral epiphysis THA – Total hip arthroplasty TKA – Total knee arthroplasty TI – Triangular index  xvii  Acknowledgements I would like to thank my supervisor, Dr. David Wilson, for his support and expertise. His encouragement and guidance pushed me to strive to always do better and allowed me to realise my potential.  I also wish to thank Dr. Michael Gilbart. His role in developing the thesis topic was key and his participation not only enhanced this thesis, but provided me with direction and support.  Thank-you to Emily McWalter. Her endless technical expertise and emotional support was invaluable and extremely appreciated.  Thanks also to Katharine Wilson, Angela Kedgley, Claire Jones, Angela Melnyk, Robyn Newell, Shahram Amiri, Honglin Zhang, Agnes d’Entremont, JD Johnston, Joshua Levitz and Laura Greaves for their guidance and advice.  Thank-you to Bradley Callan for always supporting and believing in me. Without your words of encouragement, your ability to make me laugh and your cooking I would not have been able to complete this work.  Thank-you to my family for their unconditional love and support.  I would also like to thank the Canadian Institutes of Health Research, the National Sciences and Engineering Research Council of Canada, the Canadian Arthritis Network and the Michael Smith Foundation for Health Research for their financial support.  xviii  Co-Authorship Statement A version of Chapter 2 of this thesis will be submitted for publication. This chapter was cowritten with Dr. David Wilson and Dr. Michael Gilbart.  Author contributions: Laura Given was responsible for conduction of the experiments, analysis and presentation of the findings and writing and editing of the original paper. Dr. David Wilson was the key editor on this paper and provided the original ideas behind the paper. Dr. Michael Gilbart performed the surgical procedures, provided key insight and guidance and provided editorial assistance.  xix  1 Introduction and Literature Review 1.1  Introduction Femoroacetabular impingement (FAI) is a major cause of hip pain in young adults and is  increasingly recognized as a precursor to early onset osteoarthritis (OA) of the hip [13, 24, 54, 160, 166]. Two types of FAI have been described: pincer and cam. Pincer impingement results from over-coverage of the femoral head by the acetabulum, generally due to a retroverted acetabulum [13, 54]. Cam impingement is the result of decreased concavity of the anterosuperior region of the femoral head-neck junction [76] and is often found in patients with a history of childhood hip disease such as Legg-Calvé-Perthes’ disease [153] or slipped capital femoral epiphysis (SCFE) [105], though the majority of the cases have no such history [103]. Though it is known that the morphology of deformities associated with cam FAI affects the location and severity of subsequent cartilage damage [80, 160], the reasons for this are not yet known since we do not yet understand how this lesion alters the motion and loading at the joint. The objective of this study was to determine how hip kinematics are affected by cam FAI.  1.2  The hip joint - anatomy The femoroacetabular (hip) joint is a synovial ball-and-socket joint created by the pelvis  proximally and the femur distally. The pelvis is initially comprised of three bones, the ilium superiorly, the ischium posteriorly and the pubis anteriorly, which fuse during adolescence. The articulating surface of the pelvis in the hip joint is the acetabulum, a cup-like structure formed by aspects of the ilium, ischium and pubis (Figure 1-1A).  The acetabulum is lined with a  horseshoe-shaped strip of articular hyaline cartilage (the lunate surface) which articulates with  1  the femur.  The central and inferior regions of the acetabulum, the acetabular fossa and  acetabular notch respectively, are not covered by cartilage. The articulating surface of the femur is the femoral head, which is connected to the femoral shaft by the femoral neck. The femoral head is covered by articular hyaline cartilage except for a small region, the fovea, in the center of the femoral head where the ligamentum teres femoris connects the femoral head to the acetabular notch (Figure 1-1B).  In a healthy joint, the articulating portion of the femoral head is  approximately spherical [65] and becomes concave at the edge of the articular surface as it connects with the femoral neck. More recently, it has been postulated that the shape of the femoral head more closely represents that of a rotational conchoid [116] which would result in a combined rolling and gliding motion of the femur in the acetabulum as opposed to just gliding as would be the case with a spherical femoral head, thereby lowering the friction in the joint by reducing the translation of the surface of the formal head relative to the surface of the acetabulum.  Figure 1-1: A) Lateral view of a left hemi-pelvis. B) Right proximal femur. [59]  2  The hip joint is surrounded by a fibrous joint capsule which helps to hold the femoral head in the acetabulum, and a synovial membrane which produces synovial fluid, the joint lubricant. Along with the fibrous joint capsule, four ligaments are present on the outside of the joint which strengthen the joint and limit motion, especially during extension. These are the transverse acetabular ligament, which closes the gap created by the acetabular notch; the iliofemoral ligament, which runs from the superior region of the acetabulum anteriorly across the joint to the anterior-inferior region of the femoral neck; the pubocapsular ligament, which runs from the anterior portion of the acetabulum to the inferior region of the femoral neck; and the ischiofemoral ligament which runs from the posterior acetabulum to the superior region of the femoral neck (Figure 1-2).  Figure 1-2: A) Anterior view of pelvis. B) Posterior view of pelvis. [59]  The labrum is a fibrocartilaginous structure attached to the rim of the acetabulum and continuous with the articular cartilage through a transition zone of calcified cartilage (Figure 3  1-3). The labrum is believed to a play a mechanical role in the hip joint by maintaining synovial fluid pressure in the joint [51] and by increasing the articular surface area [159]. This larger surface area likely aids in distributing load across the hip joint, sparing the cartilage from excessive loads [159].  Articular cartilage Labrum  Transverse acetabular ligament  Figure 1-3: Lateral view of the acetabulum. The labrum is continuous with the articular cartilage. The transverse acetabular ligament closes the acetabular notch. [Reprinted from Clinically Oriented Anatomy, 4th Ed. By Moore, K. and Dalley, page 609, A. with permission of Lippincott Williams and Wilkins, Inc. This material is copyrighted and any further reproduction or distribution is prohibited]  The hip is capable of six motions: flexion, extension, abduction, adduction, internal rotation and external rotation, driven by 22 muscles which cross the hip joint. The relative contribution of force driving the motion is often approximated by the physiological cross-sectional area (PCSA) of each muscle. This value is calculated by dividing the volume of the muscle by its length. The attachments, functions and PCSA’s of each muscle which crosses the hip joint are summarized in Appendix B.  4  1.3  Osteoarthritis (OA) of the hip OA is a chronic, painful and progressive disease. It begins as primary inflammation and  pain at the joint, but progresses to mechanical damage to the joint in the form of cartilage fibrillation, osteophytes and sclerosis of the underlying subchondral bone and eventually full depth cartilage loss (Figure 1-4) [140]. Symptoms include difficulty executing daily tasks due to deep, aching joint pain and joint stiffness [49]. Treatment of OA typically begins medicinally with the use of non-steroidal anti-inflammatory drugs (NSAIDs), but for more severe OA which cannot be treated by managing pain alone, joint replacement is the only option [163]. 10% of people aged 40-49 and 80% of people aged 70 and older have some type of OA, most commonly in the hands and the load bearing joints such as the knee or the hip [40, 49, 50]. Musculoskeletal diseases, such as OA, had an economic burden of $16.4 billion annually in Canada in 1998, just over 10% of the total economic burden of illness that year. $2.6 billion of this is accounted for in direct costs, such as hospital care (3% of total direct costs for all illnesses) and $13.7 billion is accounted for in indirect costs such as lost productivity (18% of total indirect costs for all illnesses) [99].  5  Figure 1-4: Osteoarthritic hip joint. [Reprinted from Osteoarthritis: A discussion paper prepared for The Workplace Safety and Insurance Appeals Tribunal by Tile, M. with permission of the Queen’s Printer of Ontario. This material is copyrighted and any further reproduction or distribution is prohibited]  OA of the hip is present in approximately 5% of the population aged 65 and older [98] and is expected to increase by 20-33% by 2030 [39]. Hip OA has traditionally been thought of as either primary, meaning that there is no known cause, or secondary to some known hip disorder. It has, however, been repeatedly suggested that primary hip OA may be extremely rare or non-existent, that patients who are diagnosed with primary hip OA actually have some previously undiagnosed minor deformity[53, 66, 122, 154]. The exact processes of initiation and progression of OA are still unknown; however, joint mechanics are thought to be a factor in both [28, 109, 110, 139, 146]. The most widely accepted mechanical theory of OA states that abnormal joint loading increases stress concentrations in the cartilage, leading to cartilage wear and degeneration [45, 54, 122, 124, 160]. Fibrillations in the cartilage increase joint friction, leading to further degeneration. Cartilage, an avascular tissue, is 6  unable to repair itself and, therefore, once the osteoarthritic disease process begins it cannot be reversed.  1.4  Femoroacetabular impingement (FAI)  1.4.1 Introduction to FAI Anterior FAI is a disorder of the hip joint where the femoral head-neck region repeatedly abuts against the rim of the acetabulum. This can be caused either by a deformity of the femur (cam FAI), a deformity of the acetabulum (pincer FAI) or both (combined FAI) [54, 7, 85, 101, 124]. Cam FAI is the result of insufficient concavity of the antero-superior femoral head-neck region [54, 76, 85, 124, 129, 157] (Figure 1-5A). This decreased concavity, known as a pistolgrip or tilt deformity, results in a jamming of the femoral head into the morphologically normal acetabulum during wide ranges of motion [47, 76, 84, 101, 129, 158]. Pincer-type FAI is caused by a deformity of the acetabulum which results in over-coverage of the femoral head [54, 76, 100, 138, 149, 150]. This over-coverage may be the result of acetabular retroversion [76, 100, 138, 149, 150], overhang of the acetabular rim [76] or increased pelvic tilt [149] (Figure 1-5B).  7  Figure 1-5: A) Cam FAI caused by nonspherical femoral head abutting against the rim of the acetabulum. B) Pincer-type FAI caused by overcoverage of the femoral head. [Reprinted from Femoroacetabular Impingement: a cause for osteoarthritis of the hip. Clinical Orthopaedics and Related Research. 2008; 417: page 113 by Ganz R, Parvizi J, Beck M, Leunig M, Notzli H and Siebenrock K with permission of Lippincott Williams and Wilkins, Inc. This material is copyrighted and any further reproduction or distribution is prohibited]  1.4.2 Etiology and epidemiology of cam FAI While the etiology of cam FAI is not yet completely understood, a number of predisposing conditions exist. These include SCFE [25, 53, 54, 76, 81, 84, 85, 105, 129, 148, 150], LeggCalvé-Perthes disease [25, 53, 54, 76, 84, 85, 129, 150], coxa magna [84, 85], congenital hip dysplasia [25, 53, 54, 76, 84, 85, 129, 150], multiple epiphyseal dysplasia [53], spondyloepiphyseal dysplasia [53], avascular necrosis of the femoral head [25, 54, 76, 129, 150], fractures of the femoral head [84, 85] and post-traumatic rotational deformities [48, 81]; however the majority of patients with cam FAI have no known history of hip disease [84]. Cam FAI is especially common in young, athletic men [54, 85, 135], with cam deformities being present in approximately 15% of all men [57] and 25% of highly athletic men [123]. Recently, it has been discovered that genetic factors influence the prevalence of cam FAI, with  8  siblings of those with cam FAI being 2.8 times more likely to also have the disorder than nonsiblings [137].  1.4.3 Diagnosis and quantification of cam FAI Cam FAI presents clinically as slow onset intermittent groin pain especially during deep flexion and is exacerbated by increased physical activity [54, 100, 138]. Decreased range of motion (ROM) especially in flexion, and internal rotation, are also common [54, 100, 138]. Confirmation of this diagnosis can be found through the passive impingement test [138] and/or imaging of the femoral head. The passive impingement test is the most common method of identifying FAI. It involves the patient lying supine while the examiner flexes the hip to 90°, then adducts and internally rotates the hip. If this motion results in groin pain the test is positive for impingement [88] (Figure 1-6). If a patient tests positive in the passive impingement test, the physician will typically confirm the diagnosis using imaging. Various imaging measures have been created to describe cam FAI.  9  Figure 1-6: The passive impingement test. The patient lies supine while the examining physician flexes the thigh to 90°, then adducts and internally rotates the leg. If the patient experiences pain, the test is positive. [Reprinted from Clinical presentation of femoroacetabular impingement. Knee Surgery, Sports Traumatology, Arthroscopy. 2007; 15: page 1042 by Philippon M, Maxwell R, Johnston T, Schenker M and Briggs K with permission of Springer-Verlag. This material is copyrighted and any further reproduction or distribution is prohibited]  The original measure, which is still in use, was the femoral head-neck offset ratio. This was first used as a measure of cam-FAI by Ito et al. in 2001 [76]. Magnetic resonance image (MRI) slices were taken perpendicular to the neck axis through the center of the femoral head and the site of potential impingement at the neck. The femoral head and neck radii were found at 22.5° intervals around the neck axis (Figure 1-7). The offset ratio was calculated for each interval according to Equation 1-1 [76] .  10  Figure 1-7: Offset ratio measurement. ORi is the offset ratio for interval i, FHI is the femoral head radius for interval i, Oi is the neck radius for interval i and R is the radius of the circle of best fit of the femoral head. [Reprinted from Femoroacetabular impingement and the cam-effect. A MRI-based quantitative anatomical study of the femoral head-neck offset. Journal of Bone and Joint Surgery, British Edition. 2001; 83: page 173 by Ito K, Minka Mn, Leunig M, Werlen S and Ganz R with permission of the British Editorial Society of Bone and Joint Surgery. This material is copyrighted and any further reproduction or distribution is prohibited]  Equation 1-1  Similar to the offset ratio, a femoral head-neck offset has been used to quantify the cam deformity [151]. Rather than finding the ratio the offset distance was calculated simply by subtracting the neck radius from the femoral head radius. While this measure may provide better information to the surgeon, allowing him to know how much bone requires resection, it is not as useful for diagnosis as the offset ratio because it is not normalized to the size of the patient’s femoral head. The current standard in quantification of cam FAI is the alpha angle. This measure was originally made on a MRI slice through the axis of the femoral neck and perpendicular to the 11  coronal plane. The alpha angle was defined as the angle between the line through the center of the femoral neck and the line joining the center of the femoral head to the point where the femoral head first exceeds the radius of the femoral head anteriorly (Figure 1-8) [129]. Using this measurement, it was found that the control group (n=35) had an alpha angle of 42.0°±2.2° whereas the patient group (n=39) had an alpha angle of 74.0°±5.4° [129]. The findings of this study led to the currently used standard of an alpha angle greater than 55° indicating the presence of cam FAI [12]. Though the alpha angle is commonly used, its usefulness is limited by the cost of MRI and that it is a two-dimensional (2D) measure in the purely anterior region of the femoral head-neck, while the cam deformity is a three-dimensional (3D) deformity which is present over the entire antero-superior region. To get around these limitations, other measures have been created which either expand on the alpha angle or measure a different aspect of the deformity.  A  B  Figure 1-8: Alpha angle measurement. A) Normal hip joint B) Hip with cam FAI. [Reprinted from The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. Journal of Bone and Joint Surgery, British Edition. 2002; 84: page 558 by Notzli H, Wyss T, Stoecklin C, Schmid M, Treiber K and Hodler J with permission of the British Editorial Society of Bone and Joint Surgery. This material is copyrighted and any further reproduction or distribution is prohibited]  Since 3D computed tomography (CT) is much more cost-effective and readily available than magnetic resonance (MR), it was desirable to determine whether the alpha angle could be  12  applied to this imaging modality. Similar results were found with the mean alpha angle being 43.8°±4.46° for the control group (n=20) and 66.4°±17.2° for the symptomatic group (n=30) [12]. This showed that it is possible to make the alpha angle measurement using CT rather than MR, making diagnosis much more cost effective.  However, this measurement still only  describes a limited portion of the deformity and CT presents significant safety risks to the patient due to exposure to radiation. To better describe the entire deformity, the alpha angle was measured using MR in eight positions radially (anterior, antero-superior, superior, postero-superior, posterior, posteroinferior, inferior, antero-inferior) [135].  They found that the largest difference in alpha angle  between patients with pincer-type FAI (thought to have normal femoral morphology) and patients with cam FAI was in the antero-superior region where the pincer-type group had an alpha angle of 66°±19° and the cam-type group had an alpha angle of 81°±15° (p=0.018). Differences were also seen in the anterior region (pincer-type: 54°±11°; cam-type: 68°±19°; p=0.005). No significant differences were observed in the remaining six regions (Figure 1-9).  13  Figure 1-9: Alpha angle differences between cam and pincer FAI in eight positions. [Reprinted from Cam and pincer femoroacetabular impingement: characteristic MR arthrographic findings in 50 patients. Radiology. 2006; 240: page 780 by Pfirrmann C, Mengiardi B, Dora C, Kalberer F, Zanetti M, Hodler J with permission of the Radiology Society of North America. This material is copyrighted and any further reproduction or distribution is prohibited]  Similarly, the alpha angle was computed using MR at 12 o’clock (superior), 1 o’clock, 2 o’clock and 3 o’clock (anterior) [141]. They found that the largest alpha angle most commonly occurs in the 2 o’clock position. More importantly, they found that 54% of the patients studied had a normal alpha angle in the 3 o’clock position, but an abnormal measurement in one of the other positions, indicating that measurements made on the oblique axial slice, as is typically performed, may not be the most indicative of a cam deformity [141].  14  Further, the alpha angle and head-neck offset were measured using three commonly acquired planar radiographs, the antero-posterior (AP), the cross-table lateral, and the frog-leg lateral [38]. Acquisition of planar radiographs is much less costly than MR and CT and exposes the patient to less radiation than CT. Significant differences were found between control and patient groups for both alpha angle and head-neck offset measurements on all three planar radiographs, indicating that any of the three could be used to detect cam FAI; however, they found that the frog-leg lateral radiograph had the highest interobserver and intraobserver agreement [38]. In 2007, a new measurement, the triangular index (TI), was introduced as an alternative to the alpha angle for AP radiographs [57]. This is a measurement of the pathologically increased femoral head radius at the point of impingement. It is found by determining the height (H) of the femoral neck at ½r from the center of the femoral head, where r is the radius of the femoral head (Figure 1-10). The pathological radius (R) is then determined using Equation 1-2.  If the  pathological radius is at least 2mm larger than the non-pathological radius, a cam deformity is determined to be present [57]. The benefit of the TI is that it encompasses the height of the deformity rather than merely the position, as is done with the alpha angle. It again, however, only describes the deformity in two dimensions.  15  Figure 1-10: Triangular index. r is the radius of the femoral head, B is the line through the center of the femoral neck, H is the height at 1/2r along B and R is the pathological radius. [Reprinted from A new radiological index for assessing asphericity of the femoral head in cam impingement. Journal of Bone and Joint Surgery, British Edition. 2007; 89: page 1311 by Gosvig K, Hebert D and Gannotti M with permission of the British Editorial Society of Bone and Joint Surgery. This material is copyrighted and any further reproduction or distribution is prohibited]  Equation 1-2  1.4.4 Cam FAI and joint damage The aspherical shape of the femoral head in a patient with cam FAI is increasingly believed to lead to joint damage, specifically labral tears and OA. Below is a review of the literature describing the relationship between cam FAI and hip joint damage.  1.4.4.1 Cam FAI and labral tears Labral tears cause pain in the anterior hip or groin area as well as painful clicking during motion [29, 68, 88, 114]. Labral tears have been shown to cause OA, likely due to the reduction 16  in contact area and the increase in joint friction and instability [6, 30, 42, 52, 55, 66-68, 96, 104, 113, 114, 117, 128, 133, 146]. Cam FAI is a known cause of these labral tears [14, 48, 75, 76, 105, 106, 124, 133]. During large ranges of motion, the aspherical femoral head is jammed into the acetabulum, causing the labrum to become detached from the bone [54, 76, 100, 101, 129].  1.4.4.2 Cam FAI and OA of the hip The first of three classic studies which initially examined the relationship between cam FAI and hip OA was performed by Murray in 1965 [122]. He studied 200 patients with so-called primary hip OA and 100 control hips. They found that 65% of the primary cases were actually secondary to a pre-existing asymptomatic abnormality of the femur. He named this deformity the tilt deformity [122]. In 1976, Solomon had a similar finding in his South African population of 327 cases of hip OA. Of these, 65 had a history of hip disease (Legg-Calvé-Perthes, congenital dysplasia or severe trauma). Another 38 had rheumatoid arthritis, 43 had post-inflammatory degenerative arthritis, 24 had a history of osteonecrosis of the femoral head and 4 had other bone disorders. The remaining were initially classified as primary hip OA. Of these, he found that on closer inspection, 67 had acetabular dysplasia, and 59 had what Murray had named the tilt deformity. The remaining 27 had no evidence of hip deformity [154]. Further, in 1986, Harris went even further to speculate that 90% of adult primary OA was actually secondary to subtle deformities after a retrospective study looking at radiographs from 75 patients with so-called primary OA[66]. He found that within this population, a typical deformity of the femoral head-neck region was present which involved a flattening of the concave lateral femoral neck, the development of a bump on the anterolateral surface of the 17  femoral neck and the formation of a hook at the junction of the articular surface of the femoral neck. He named this deformity the pistol-grip deformity. Since these classic studies, investigators have sought to understand whether FAI is causing hip OA or vice-versa. Ganz, et al. (2008) stated that in order to determine that FAI is causing OA three major pieces of evidence are still required. The first is a large-scale longitudinal clinical study of asymptomatic adults which documents the percentage of whom have abnormalities typical of cam FAI and how many develop OA in the future.  Second, the  mechanism by which deformities lead to OA needs to be established. Third, a method of treating the deformity which halts or delays the progression of OA needs to be developed and confirmed [53].  1.4.5 The causal relationship between cam FAI and hip OA While the large-scale prospective studies have yet to be performed, many retrospective studies have supported the FAI theory [10, 13, 44, 80, 160, 162]. AP, cross-table lateral and frog-leg lateral radiographs from 200 patients undergoing total hip arthroplasty (THA) were studied [162]. 38% of these patients had hip OA secondary to avascular necrosis (19%), trauma (7%), developmental dysplasia (5%), rheumatism (4%), protrusion (2%) or Legg-Calvé-Perthes disease (1%). The remaining 62% were classified as primary. Of these, 100% were found to have a cam deformity (43% had a mild deformity, 32% moderate and 25% severe) [162], further supporting the findings of Murray, Solomon and Harris, but not indicating whether cam FAI was causing OA or whether it was a symptom of OA. Further, conventional radiographs and CT image series from the contralateral hips of 119 patients who underwent THA were studied [44]. Of these, 94 had early OA and 25 had healthy  18  joints. Alpha angles were measured for each hip as well as a subjective identification of a bony prominence at the head-neck junction. They found that alpha angles of greater than 50° were correlated with presence of hip OA (odds ratio 1.09, p=0.003). They also found that hips in the arthritic group were more likely to have a bony prominence at the head-neck junction (40% with arthritis, 12% without arthritis, p=0.006). Since this study looked at early OA rather than late OA as had previously been done, these results indicate that it is more likely that cam FAI is causing OA rather than a symptom of it; however since this is a retrospective study it cannot be proven. A computer simulation of hip motion (HipMotion, Bern, Switzerland) was used to determine the predicted location of cartilage damage using CTs of 15 hips and compared this location to the location of labrum and cartilage damage observed 40 hips intraoperatively during open osteochondroplasty (discussed in section 1.4.7 below) [160]. No difference was found between the mean observed and predicted locations; however, the observed location was much larger than the predicted location (Figure 1-11). The reason for this is likely that the simulation stops as soon as impingement is detected and ignores soft tissue deformation (validity of this model is discussed in section 1.5.4.4 below). This study began to relate the hypothesized mechanism of FAI leading to OA to the causation issue described above. While it is still not a prospective study, the ability of the model to predict the location of damage further indicates that cam FAI is causing OA.  19  Figure 1-11: Distribution of labral and chondral damage sites. [Reprinted from Hip damage occurs at the zone of femoroacetabular impingement. Clinical Orthopaedics and Related Research. 2008; 466: page 278 by Tannast M, Goricki D, Beck M, Murphy S and Siebenrock K with permission of The Association of Bone and Joint Surgeons. This material is copyrighted and any further reproduction or distribution is prohibited]  The first retrospective study was performed in 2009 in an attempt to determine the causal relationship between cam FAI and hip OA. Two anteroposterior (AP) radiographs from 43 patients under 55 years of age with a history of symptomatic idiopathic OA at the second radiograph with the first radiograph from at least 10 years prior were analyzed [10]. No relationship between the AP-alpha angle in the first radiograph and progression of OA in the second radiograph was found; however, it is known that the ability to identify cam deformities on AP radiographs is very poor since the deformity is centered at in the anterosuperior region, not the superior region [53] and a very small sample size was used.  1.4.6 The mechanism of joint damage in cam FAI While it has yet to be proven that cam FAI is causing OA through large-scale prospective studies, the mechanism by which cam FAI might lead to hip OA is beginning to be understood. 20  For large deformities, cartilage damage is thought to be caused by excessive contact stress occurs at the point of impingement. For mild deformities, however, the mechanism is more subtle. It is thought that during large ranges of motion, the non-spherical portion of the femoral head jams into the acetabular cavity, resulting in increased shearing of the cartilage from the labrum and subchondral bone (Figure 1-12) [54].  Figure 1-12: Illustration of the mechanism of joint damage in cam FAI. [Reprinted from Anterior femoroacetabular impingement: part I. Techniques of joint preserving surgery. Clinical Orthopaedics and Related Research. 2004; 418: page 62 by Lavigne M, Parvizi J, Beck M, Siebenrock K, Ganz R and Leunig M with permission of Lippincott Williams and Wilkins, Inc. This material is copyrighted and any further reproduction or distribution is prohibited]  To confirm this mechanism, recent studies have looked at cartilage health at the location of jamming in younger patient groups. Cartilage samples from 22 patients who underwent surgery for cam FAI were studied and compared them to age matched controls (ages 19-45, mean 30.4 years). It was found that all of the samples from the patient group showed signs of early histological OA but the controls did not [166].  More recently, three studies have shown  correlations between dGEMRIC (delayed Gandolinium Enhanced Magnetic Resonance Imaging Contrast) and cam FAI [23, 24, 78], indicating that this jamming effect is decreasing the glycosaminoglycan content in the cartilage, thereby increasing the rate of progression of OA. 21  1.4.7 Treatment of cam FAI Conservative treatment of FAI typically includes activity modification, such as restricting excessive hip motion, and NSAIDs [101]. Though physical therapy is often prescribed, it is thought to be counter-productive and may aggravate the problem by increasing labral and cartilage damage [101]. While conservative treatments may limit progression of joint damage by limiting the contact between the deformity and the cartilage and labrum, they do not repair the damage that has already been done. Surgical treatment of cam FAI, known as resection osteochondroplasty, involves removing the impinging bony deformity to restore the femoral head-neck offset and clearance for hip motion [101, 157, 158].  This surgery can be done either open by dislocating the hip or  arthroscopically [14, 48, 101, 121, 157]. While the arthroscopic technique is less invasive and poses less risk of complications, the surgeon is more likely to either under or overcorrect the problem due to lack of visibility, though this is related to the surgeon’s level of experience [112]. Removing more than 30% of the diameter of the neck significantly increases the risk of fracture [111]; however, undercorrection can lead to residual impingement and the need for a second surgery in the future [77, 101]. A summary of clinical outcomes created by Jaberi and Parvizi in 2007 is presented in Table 1-1. More recent outcomes are presented in Table 1-2 [74, 134, 157]. While it is clear that resection osteochondroplasty is successful reducing pain and improving quality of life in patients with cam FAI, it is still unknown how cam deformities are affecting hip kinematics and loading.  The fact that surgical correction of the morphology reduces pain  indicates very strongly that the deformity is creating changes in the joint mechanics; however the exact changes and, therefore mechanism by which cam FAI is leading to OA, are not yet fully understood.  22  Table 1-1: Clinical outcomes of surgical treatment of FAI syndrome. [Reprinted from Hip pain in young adults: femoroacetabular impingement. Journal of Arthroplasty. 2007; 22 (7 Supp. 3): page 40 by Jaberi F, Parvizi J with permission of Elsevier Inc. This material is copyrighted and any further reproduction or distribution is prohibited]  23  Author(s)  Year (Journal)  No. of Patients /Hips 29 patients/ 30 hips  Age. Mean (y) 31 (1651)  Open surgical dislocation of hip  Peters et al.  2006 (J Bone Joint Surg Am)  Arthroscopic management  Stahelin et al.  2008 (Arthroscopy)  22  Ilizaliturri Jr. et al.  2007 (J Bone Joint Surg Br)  13 patients/ 14 hips  Treatment modality  Follow -up  Osteoplasty of femoral neck; labral debridement (7 patients); labral refixation (5 patients)  24 m  42 (1867)  Osteoplasty of femoral neck; labral debridement  6m  30.6 (2439)  Osteoplasty of femoral neck; acetabular and labral debridement  24 m  Table 1-2: Recent clinical outcomes of surgical treatment of FAI syndrome.  24  Results  Avg. 70 points improvement on Harris hip score (20-81 points); 13% failures due to pain and/or progressive OA; no AVN 17 had no impingement post-operatively; 8 had no pain at follow-up  1 failure; Improved WOMAC score by 9.6 (4 to 14); No fracture or AVN  Comments  Safe, does not jeopardize vascularity of femoral head  Good results even with insufficient alpha angle correction Longer followup required  1.5  Hip kinematics  1.5.1 Anatomical coordinate systems Joint kinematics are typically described using one of three methods: Euler or Cardan angles, helical axes, or floating axes. Each of these methods uses a standard joint coordinate system where the positive X-axis is defined as anterior, the Y-axis is defined as superior and the Z-axis is defined as to the right.  In the hip, both the pelvic coordinate system and the femoral  coordinate system have their origin located at the center of the femoral head (either the rotational center or the geometric center). The Z-axis of the pelvic coordinate systems is defined as being parallel to the line joining the two anterior superior iliac spines (ASIS), the X-axis is defined as parallel to a line lying in the plane defined by the two ASIS and the two posterior superior iliac spines (PSIS) and perpendicular to the Z-axis, the Y-axis is defined as perpendicular to both the X and Z axes (Figure 1-13) [169]. The Y-axis of the femoral coordinate system is defined as joining the midpoint of the two femoral epicondyles (FEs) with the origin, the Z-axis is defined as parallel to the line joining the two FEs and perpendicular to the Y-axis, and the X-axis is defined as perpendicular to both the Y and Z axes (Figure 1-13) [169].  25  Figure 1-13: Hip joint coordinate systems. [Reprinted from ISB recommendation on definitations of joint coordinate system of various joints for the reporting of human joint motion – part I: ankle, hip and spine. International Society of Biomechanics. Journal of Biomechanics. 2002; 35: page 546 with permission of Elsevier Science Ltd. This material is copyrighted and any further reproduction or distribution is prohibited]  Euler or Cardan angles represent joint kinematics as a combination of three rotations and three translations of the coordinate system fixed to the femur about the coordinate system fixed to the pelvis. Translations are defined by motion of the femoral origin along each of the pelvic axes. Euler angles represent rotations about a two axis system: a rotation about one axis, followed by a rotation about a second axis, then a rotation about the first axis. Cardan angles, on the other hand, represent a motion as a combination of rotations about the three different axes. In the hip, a 3-1-2 rotation sequence is typical, meaning a rotation about the Z-axis  26  (flexion/extension), followed by a rotation about the X-axis (abduction/adduction), followed by a rotation about the Y-axis (internal rotation/external rotation) (Figure 1-14). With both Euler and Cardan angles, the order of rotation matters.  Figure 1-14: Cardan angle coordinate system rotations. The first rotation, α, is about the Z-axis (red), the second rotation, β, is about the new X-axis (blue) and the third rotation, γ, is about the new Y-axis (purple). [Reprinted from Use of cardan angles to locate rigid bodies in three-dimensional space. Medical and Biological Engineering and Computing. 1987; 25: page 528 by Tupling S and Pierrynowski M with permission of the International Federation for Medical and Biological Engineering. This material is copyrighted and any further reproduction or distribution is prohibited]  Helical axes represent motion as the unit vector of the instantaneous axis of rotation, the angle of rotation about this axis and a translation along this axis (Figure 1-15) [168].  This  method eliminates the problem of order; however large errors in accuracy are present with small motions, often misrepresenting the axis of rotation.  27  Figure 1-15: Helical axis representation of rotations and translations. Motion is represented as a combined rotation about and translation along a single axis (d). [Reprinted from 3-D attitude representation of human joints: a standardization proposal. Journal of Biomechanics. 1994; 27: page 1403 by Woltring H with permission of Elsevier Science Ltd. This material is copyrighted and any further reproduction or distribution is prohibited]  Floating axes are a method of representing motion as a combination of three rotations and three translations in which the order of rotation does not matter [62]. In this method for the hip, a long axis is defined as the Y-axis in the femur (e3), a flexion axis is defined as the Z-axis in the pelvis (e1) and a third axis, the floating axis, is defined as the cross product between the long axis and the flexion axis (e2) (Figure 1-13). Translation is represented as motions along each of these axes. Flexion is defined as the angle about the flexion axis, between the floating axis and X-axis of the pelvis; abduction is defined as the angle about the floating axis, between the long axis and the Y-axis of the pelvis; and internal rotation is defined as the angle about the long axis,  28  between the floating axis and the X-axis of the femur [169]. This is the method recommended by the International Society of Biomechanics [169].  1.5.2 Center of the hip Defining an accurate origin for studying hip joint kinematics is important for calculating required muscle forces and joint loading as well as for understanding translations in the joint [152]. The origin of the hip joint is standardized as the center of rotation (COR) [169]. The COR can be determined using bony landmarks, radiographically, or functionally. Location of the COR using bony landmarks is the method often used during in vivo gait analysis studies [8, 15, 16, 145, 165]. It involves identifying the location of bony landmarks on the pelvis and femur by palpation and estimating the location of the hip joint center from these landmarks. The two most popular methods are Andriacchi’s approach [8] and Tylkowski’s approach [165]. Andriacchi’s approach defines the center of the hip to be 1.5-2cm distal to the midpoint of a line joining the pubic symphysis and the ASIS in the frontal plane and directly medial to the greater trochanter [8]. Tylkowski’s approach defines the center of the hip joint to be 11% of the distance between the ASIS medial to the ASIS, 12% distal to the ASIS and 21% posterior to the ASIS [165]. These estimates of the hip joint center are very useful in vivo since they do not require radiographs or complex calculations; however, the accuracy of these methods is severely limited due to differences in bony morphology between subjects. Determination of the COR using radiographic methods relies on the assumption that the COR is located at the center of the femoral head. This method has been used for computer simulations of hip joint motion [95, 160, 161] and during THA and TKA (total knee arthroplasty) [73, 87, 107]. In this method, a sphere is fit to the femoral head and the center of the sphere is used as  29  the hip joint center. This is the gold-standard in Computer Assisted Systems [108]. This method is useful when the functional methods described below are not possible; however it relies on an unproven assumption. Functional methods of finding the COR involve tracking the motion of the femur and fitting a sphere to the marker positions. The COR is defined as the center of this sphere. This method is used in gait analysis studies [31-34, 72, 87, 94, 108, 115] and during surgical interventions such as THA and TKA [46, 94, 108, 152]. The accuracy of this method in vivo was assessed using the radiographic method as the gold standard. An average difference of 3.79cm (±1.9cm) between the COR and the radiographic center of the femoral head was found [16]. It has been proposed that almost all of this error is due to soft tissue artifact since the markers were placed on the surface of the skin , but there are also small errors due to photogrammetry (1-5mm) [34]. It is also possible that some of this “error” may be due to the COR not being coincident with the radiographic center. While this method is most commonly performed in vivo, its most useful application is more likely ex vivo since soft tissue artifact can be eliminated. It is unclear from the literature to what extent errors in calculation of the hip joint center using the functional method during large ranges of motion are due to increased soft tissue artifact and to what extent they are due to translation of the femoral head within the acetabulum. The first study to assess the extent to which the hip joint may be considered a spherical ball and socket joint was published in 2010 [35]. In this study, eight markers on the femur and four markers on the pelvis were tracked using stereophotogrammetry in 8 hip specimens (four subjects) during passive motion of the femur. It was reported that between 20° and 70° of flexion, 0° and 45° of abduction and 0° and 30° of internal rotation the hip can be considered a spherical ball and socket joint [35]. It is unclear from this paper, however, what ROM the  30  specimens were tested under, whether motion of the pelvis was considered, the age of the specimens, what happens to the motion outside of these ranges of motion, or what the accuracy of their measurements was. The accuracy of one method for determining the hip center using bony landmarks has been evaluated by comparing this method to the functional method ex vivo.  It was found that  Andriacchi’s approach was accurate to within 3.61cm (0.73cm in the X-direction, 1.61cm in the Y-direction, 2.88cm in the Z-direction) and that the accuracy of Tylkowski’s approach was within 1.90cm (1.66cm in the X-direction, 0.47cm in the Y-direction, 0.63cm in the Z-direction) [16]. From this, recommendations were made that if bony landmarks must be used to predict the center of the hip joint, a combination of Andriacchi’s approach and Tylkowki’s approach should be used, where the X-value is determined using Andriacchi’s approach and the Y and Z values are determined using Tylkowski’s approach. It was found that this method allowed for an overall accuracy of within 1.07cm [16].  1.5.3 Translational motions of the hip joint Due to the widely used but unvalidated assumption that the hip joint is a spherical ball and socket joint, literature does not exist on the translations of the femoral head with respect to the pelvis. To my knowledge, only one study has looked at the translation of the anatomical center of the femoral head during passive motion. Functional methods of calculating the center of the femoral head were compared to radiographic methods [108]. The femur of each of eight cadaveric hip specimens was passively moved in various planes while the motion of three passive optical markers were tracked using an intraoperative navigation system (BluIGS/KLEE – Orthokey, Delaware, DE, USA). They found that the anatomical center of the femoral head  31  found by fitting a sphere to the digitized surface of the femoral head moved over 5mm laterally during passive flexion and internal/external rotation (exact value not reported) at flexion angles of approximately 100° (Figure 1-16) [108]. This implies that either the anatomical center of the femoral head is not the COR or that the hip joint is not spherical.  Figure 1-16: Rotations and translations of the hip joint during passive flexion. [Reprinted from Evaluation of formal methods in hip joint center assessment: an in vitro analysis. Clinical Biomechanics. 2010; 25: page 210 by Lopomo N, Sun L, Zaffanini S, Giordano G and Safran M with permission of Elsevier Ltd. This material is copyrighted and any further reproduction or distribution is prohibited]  32  1.5.4 Rotational motions of the hip joint Studying the rotational motions of the hip joint has been the major focus of hip joint kinematics. Studies have been performed in vivo, ex vivo (in cadavers), in vitro (in prostheses) and using computer simulations. In vivo studies have historically looked at the motions of the lower extremity during various tasks, but have more recently been applied to help understand the effect that joint deformities have on these motions. Ex vivo studies are rare but have focused on determining the COR of the native hip joint, in vitro studies have been performed to test hip joint prostheses, and computer simulations have been performed to determine ROM to impingement in both normal and deformed joints. 1.5.4.1  In vivo measurements of rotational kinematics  The gait pattern of walking, being the most commonly performed repetitive motion [167], has been extensively studied in vivo [22, 37, 56, 102, 156]. These studies typically determine the rotations of the pelvis, hip, knee and ankle. Pelvic rotations are described as pelvic tilt (rotation in the saggittal plane), obliquity (rotation in the coronal plane) and rotation (rotation in the horizontal plane) relative to the global system. Hip and knee rotations are described as flexion, abduction and internal rotation of the femur with respect to the pelvis and the tibia with respect to the femur, respectively. Ankle rotations are described as dorsiflexion of the foot relative to the tibia and progression (angle of the foot with respect to the direction of progression). Only one study, to my knowledge, has compared hip and pelvic kinematics during gait in persons with and without FAI. This study compared the gait of 17 patients diagnosed with unilateral cam FAI to an age matched control group of 14 persons [86]. Retro-reflective markers were placed on anatomic landmarks according to the methodology outlined by Kadaba et al. (1990) [82], with markers placed on the left and right ASIS, the top of the sacrum, the greater 33  trochanter, the lateral edge of the estimated flexion axis of the knee, the lateral malleolus, the space between the second and third metatarsal heads, midthigh and midshank. Positions of these markers were tracked using seven VICON MX-13 cameras (VICON, Los Angeles, CA USA) at a rate of 200Hz while participants walked at their natural speed. Hip joint angles were calculated using Cardan angles with flexion/extension being the first rotation, followed by abduction/adduction and internal/external rotation [82]. Results show that the cam FAI group had a significantly lower peak abduction angle (p=0.0009) and less total frontal hip ROM (p=0.003) (Figure 1-17), lower sagittal hip ROM (p=0.047) (Figure 1-18) and lower ROM of pelvic obliquity (p=0.004) (Figure 1-19) [86]. The interpretation of these results is yet to be determined; however, the changes in gait due to cam FAI are thought by the investigators to be a compensatory strategy rather than due to limited mobility because the abduction angle achieved during gait is substantially smaller than the patient’s maximal abduction angle [86]. Either way, changes in gait will result in changes in loading patterns of the hip joint which may result in loading of cartilage areas that had previously not been loaded as heavily and therefore are less capable of carrying load. This may result in cartilage degeneration, initiating the osteoarthritic process.  34  Figure 1-17: Mean (+/- standard deviation) frontal hip angles of FAI and control groups during level gait. [Reprinted from Femoroacetabular impingement alters hip and pelvic biomechanics during gait: Walking biomechanics of FAI. Gait and Posture. 2009; 30: page 42 by Kennedy M, Lamontagne M and Beaule P with permission of Elsevier B.V. This material is copyrighted and any further reproduction or distribution is prohibited]  Figure 1-18: Mean (+/- standard deviation) sagittal hip angles of the FAI and control groups during level gait. [Reprinted from Femoroacetabular impingement alters hip and pelvic biomechanics during gait: Walking biomechanics of FAI. Gait and Posture. 2009; 30: page 43 by Kennedy M, Lamontagne M and Beaule P with permission of Elsevier B.V. This material is copyrighted and any further reproduction or distribution is prohibited]  35  Figure 1-19: Mean (+/- standard deviation) frontal pelvic anlges of the FAI and control groups during level gait. [Reprinted from Femoroacetabular impingement alters hip and pelvic biomechanics during gait: Walking biomechanics of FAI. Gait and Posture. 2009; 30: page 43 by Kennedy M, Lamontagne M and Beaule P with permission of Elsevier B.V. This material is copyrighted and any further reproduction or distribution is prohibited]  Kinematics of the hip have also been studied in vivo during other activities of daily living [8, 71, 79, 97] such as stair climbing, kneeling and squatting. One study compared hip joint kinematics during maximum squat in persons with and without cam FAI [97]. They studied 16 patients diagnosed with cam FAI and 16 controls, matched by age. Markers were placed in the same positions as above, with the same camera set-up. Hip joint kinematics were calculated using Cardan angles (flexion/extension, then abduction/adduction, then internal/external rotation). While no significant difference was seen in the hip flexion angles between the patient and control groups, significant differences in the maximum squat depth (32.3 +/- 6.8% of leg length for the control group compared to 41.5 +/- 12.5% for the patient group, p=0.037) and pelvic tilt angles were observed (Figure 1-20) [97]. While the researchers in this study state that “since pelvic orientation does not directly contribute to squat depth, it was not responsible for the discrepancy in squat depth,” [97] another possible explanation is that since the femoral angles 36  are measured with respect to the pelvis, the total flexion between the femur and the global system would be decreased with decreased pelvic recline, leading to decreased squat depth.  Figure 1-20: Mean (+/- standard deviation) pelvic tilt of FAI and control groups. [Reprinted from The effect of cam FAI on hip and pelvic motion during maximum squat. Clinical Orthopaedics and Related Research. 2009; 467: page 647 by Lamontagne M, Kennedy M, Beaule P with permission of The Association of Bone and Joint Surgeons. This material is copyrighted and any further reproduction or distribution is prohibited]  1.5.4.2 Ex vivo measurements of rotational kinematics A limited number of studies have looked at hip joint rotational motions in cadavers. Most were done with the goal of determining the COR and did not report the rotation patterns since motions were prescribed passively [34, 35, 89, 108]. Active motion simulation through muscle simulation has not, to my knowledge been performed in the hip joint. Simulating active muscles is important not only because muscle force is the primary contributor to joint load [17, 18, 19, 20, 21], but also because it has been shown that the pelvis deforms due to muscle loading, 37  creating a different loading environment within the hip joint [11]. Further, studying coupled motions at the hip can only be achieved through muscle actuated motion.  1.5.4.3 In vitro measurements of rotational kinematics In vitro studies have been performed which look at hip motion in hip prostheses [7, 36, 63]; however most of these have focused on wear by simulating walking [2-4, 26, 125-127, 143, 144]. These studies will not be discussed further as they are not relevant to the current project.  1.5.4.4 Computer simulations of rotational kinematics Three well known 3D computer simulations of hip motion have been developed, each making different assumptions about the motion of the hip. The first attempted to model the accurate motion of a normal hip joint [83]. A 3D bone surface was created from CT images. From these, an initial hip joint center was estimated using the median geometric center of the femoral head. The femur was rotated 15° in each direction (flexion, extension, abduction, adduction, internal rotation, external rotation). If any collisions were detected during these motions, a new center was chosen from within a 3mm cube located at the anatomical center of the femoral head. The center which allowed for no collisions with a 15° ROM and kept a constant distance between the femoral head and the acetabulum was chosen as the “true” center. Using this “true” center, maximum internal/external rotations, flexion/extension and abduction/adduction were simulated. They found that the flexion/extension motion was most sensitive to variances in the hip joint center location, followed by abduction and adduction, though this was not quantified [83].  The calculated ranges of motion were not reported,  38  however, from their figures it is clear that the ranges were well beyond physiologic ROM (Figure 1-21).  A  B  C  Figure 1-21: Simulation of hip joint ranges of motion. A) Full flexion. B) Full abduction. C) Full adduction. [Reprinted from Accurate simulation of hip joint range of motion. Proceedings of the IEE Computer Animation. 2002; page 217 by Kang M, Sadri H, Moccozet L, Magnenat-Thalmann N and Hoffmeyer P with permission of IEEE. This material is copyrighted and any further reproduction or distribution is prohibited]  A second model provided more physiologic results than the first; however problems with determination of the COR still existed [83, 142]. This model was used to determine how severity of SCFE affected ROM of the hip joint. Again, 3D surfaces were reconstructed from CT images; collision detection was used to determine the extent of motion which was possible. An iterative approach was used to determine the center of the joint. The iterative approach used in this model involved choosing an arbitrary initial center, preferably close to the true center. Motion was simulated in small increments around the arbitrary center while maintaining contact between the femoral head and acetabulum.  After each step, the femoral head was “forced” into the  39  acetabulum to ensure cartilage-cartilage contact by translating the femoral head medially until collision, then translating the femur to the neighbouring voxels in the transverse plane. If collision with anything other than the acetabulum occurred this position was considered to be the ROM. Otherwise, the femoral head was moved 1mm from the acetabulum and rotation about the arbitrary center was attempted. If rotation was possible, the femur was again forced into the joint and the process was repeated. If rotation was not possible due to collision with the acetabulum, the femur was moved another millimeter away from the acetabulum and the rotation was repeated until possible [142]. The benefit of this model is that it makes no assumptions about the location of the COR, in fact the center is not fixed and can move throughout the motion, making this model well suited for non-spherical femoral heads. This model, however, has not been validated and is likely to over-predict ranges of motion due to the lack of soft tissue and the possibility of supra-physiologic translations. The third model, which was developed to study cam FAI, is claimed to be validated [161]. This model, named HipMotion, again used CT images to create 3D surfaces of the femur and pelvis; but in contrast to the other two models, this model uses a fixed COR located at the anatomical center of the femoral head [161]. The femur was rotated about this point until bony contact occurred between the femur and pelvis. This model was validated using 14 cadaveric and 13 plastic hips. Optoelectronic markers were placed on the femur and acetabulum and passive motion was prescribed. It was found that the computer simulation was accurate to -0.7° ± 3.1° (-9° to 6°) using the plastic hips and -5.0° ± -5.6° (-19° to 7°) using the cadaveric hips [161]. The investigators believe that this model overpredicted the range of motion during validation due to the lack of soft tissue interaction. This validation may be applicable to normal hips, though a 19° overprediction in ROM is very large; however, it seems difficult to extend this  40  validation to deformed hips because all of the cadaveric specimens used had “preserved concentric joint morphology” which is not the case in hips with cam FAI. Despite the lack of validation in deformed hips, the HipMotion model has been used to compare ranges of motion between groups with cam FAI and controls [161], to determine the location of the impingement zones [95] and to compare the predicted location of cartilage damage to the observed location (described in section 1.4.5 above) [160] all in hips with cam FAI.  1.6  Hip loading Loading and pressure distribution have been studied in “normal” cadaver hips.  While  loading of hip joints with deformed femurs has not yet been studied, a summary of hip joint loading is provided below.  1.6.1 Mechanical methods The most commonly used method to measure contact stresses in the ex vivo hip joint is using pressure sensitive film. This has been used to measure the pressure distribution in the hip during simulated walking [1, 5, 118] and simulated one-legged stance [11, 64, 90-93, 130-132]. Limitations of this method include that the film tends to change the mechanics of the hip due to its thickness (the thinnest available is 0.3mm) [170]. This thickness, combined with stiffness effects have been shown to change the maximum contact pressures in the hip by up to 28% [170]. While pressure sensitive film has been employed to study the effect of various pelvic injuries and surgeries on hip contact loading [64, 91-93, 130, 131], it has not, to my knowledge, been used to study the effect of femoral deformities on contact loading nor has it been used to  41  study any loading scenario outside of simulated walking or one-legged stance since pressure sensitive film cannot be employed during dynamic motion scenarios. Another method used an array of piezoresistive transducers to measure the pattern of load transmission through the femoral head [26].  This method allowed for instantaneous  measurement of loads, enabling the study of contact stress in the hip during variable loading. It is, however, severely limited by the need to inlay the transducers in the cartilage, thereby inherently changing the loading environment and preventing this method from being used in vivo. Hip joint measurements have also been made in vivo using prostheses instrumented with various strain gauges to allow measurements of the force transmission through the proximal femur. Due to its in vivo nature, this method allows for measurements during true physiologic conditions such as walking, running, stair-climbing and load carrying [17-21, 41, 58, 69, 70, 120, 155]; however, these studies are limited due to the low number of participants, inability to measure load distribution and the replacement of the native hip environment with a cartilagemetal interface. These studies have, however, been very useful in our understanding of the magnitude and direction of forces in the hip. This method cannot be used to study the effect of femoral deformities on hip loading because it requires replacement of the femoral head.  1.6.2 Imaging methods Roentgen stereo photogrammetric analysis (RSA) has been used to measure 2D cartilage [9] and 3D labral [43] deformations during loading. The cartilage and labrum are not typically visible in radiographs. RSA methods involve tracking the position of metallic beads within the bone [9] or labrum [43] to determine how far the cartilage or labrum must have deformed. This  42  method is not typically performed in vivo due to concerns regarding patient safety during radiographic imaging especially when extremely high resolution is required, such as in the case of RSA. More recently, quantitative Magnetic Resonance Imaging (qMRI) has been used to map hip cartilage strain ex vivo [60, 61]. This method uses ultra high-resolution MRI of cartilage before, during and after loading to map cartilage strain due to static joint loading. 7T MR was used which allowed for visualization of the interface between the cartilage and subchondral bone. This allowed for accurate 3D quantification of cartilage deformation [60]. This method was then applied to determine the effect of labral tears and the two most common treatments for labral tears (repair and resection) on cartilage strain in cadaver human hips loaded to 2.3 times body weight [61]. It was found that labral tears did not significantly increase cartilage strain, but resection of the labrum did [61]. This method has many advantages that may in the future allow for studying how bony deformations affect joint loading since it does not pose a health risk to participants in an in vivo study and allows for 3D mapping of the strain; however, scan times are still too long and the bore size is too small to allow for in vivo studies and the small bore size does not allow for studying any position of the femur in the acetabulum other than single leg stance.  1.6.3 Models and simulations Finite element modeling (FEM) allows for quantification of the effect of changing various parameters such as bone geometry. It is severely limited, however, by the inability to validate its results in the laboratory and the sensitivity of FEM to material properties that are not yet fully understood, such as that of cartilage and the cartilage-bone interface. This method has not, to my  43  knowledge, been used to quantify how morphological changes to the hip joint effect joint loading.  1.7 Summary and directions   OA of the hip is thought to be secondary to changes in joint biomechanics. The only method of treatment of late OA is total hip replacement. Preventing or slowing OA progression requires identifying and correcting the joint biomechanics in disorders.  Cam FAI is correlated with hip OA, with as many as 90% of the cases of primary hip OA actually being secondary to cam FAI.  The mechanism of joint damage is  hypothesized to be a jamming of the aspherical femoral head into the acetabulum, resulting in increased contact stress; however this mechanism has yet to be demonstrated and it is unclear if this is the only mechanism involved in cartilage degeneration.  Cam FAI is often treated using a resection osteochondroplasty which is known to improve quality of life by reducing pain. It is unclear, however, how this surgery affects joint mechanics and whether it is able to slow or prevent the osteoarthritic disease process.  It is clear that hip kinematics are altered by the presence of cam FAI both in vivo and using computer simulations. It is unclear, however, whether mechanics are altered throughout the entire range of motion or only at the extremes of motion. Further, it is unclear whether changes in hip kinematics observed in vivo are due to pain or bony contact between the deformity and acetabulum or soft tissues.  44  In light of the current state of literature in the field, the following research questions were asked: 1) How does the severity of cam FAI affect the kinematics of the hip during flexion and abduction? 2) How does a resection osteochondroplasty of the femur affect the kinematics of the hip during flexion and abduction?  It was hypothesized that increased severity of deformity would result in increased translation of the average COR. It was also hypothesized that increased deformity would result in increased adduction and external rotation during flexion and increased extension and external rotation during abduction. It was further hypothesized that increased deformity would require increased force to create motion. Finally, it was hypothesized that resection osteochondroplasty would result in changes to kinematics which follow the same pattern as above where the resected group is considered to have a less severe deformity than the native group.  45  1.8  References  1. Adams D, Kempson G, Swanson S. Direct measurement of local pressures in the cadaveric human hip joint. Med Biol Eng Comput. 1978;16:113-115. 2. Affatato S, Bersaglia G, Junqiang Y, Traina F, Toni A, Viceconti M. The predictive power of surface profile parameters on the amount of wear measured in vitro on metal-onpolyethylene artificial hip joints. Proc Inst Mech Eng H. 2006;220:457-464. 3. 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J Biomech Eng. 1998;120:655-659.  57  2 Effect of Cam FAI on Hip Joint Kinematics 2.1 Introduction FAI is a major cause of hip pain in young adults and is recognized as a precursor to early OA of the hip [2-4, 19, 22]. Two types of FAI have been described, pincer and cam [2, 4, 6]. Pincer impingement results from an over coverage of the femoral head by the acetabulum, generally due to a retroverted acetabulum [2, 4]. Cam impingement is the result of decreased concavity of the antero-superior region of the femoral head-neck junction [6] and is found in patients with a history of childhood hip disease such as Legg-Calvé-Perthes’ disease [18] or SCFE [13], though the majority of the cases have no such history [12]. It has been hypothesized that the deformity associated with cam FAI causes high shear forces within the articular cartilage resulting from jamming of the aspherical portion of the femoral head into the more spherical acetabulum [4]. Testing this hypothesis and predicting the effectiveness of surgical treatments designed to correct cam deformities requires assessments of hip biomechanics. In one approach to studying hip biomechanics, models developed using CT images to recreate 3D surfaces of the femur and pelvis were used to determine the ranges of motion (ROM) and locations of impingement in patients with cam FAI, which were compared to the locations of damage observed intraoperatively [19].  While these models were able to predict the mean  location of damage accurately, they predicted a much smaller region of damage than was found intraoperatively [19]. One limitation of this approach is that the models relied on the assumption of a fixed centre of hip rotation, and it is currently unknown whether this assumption is valid for hips with cam deformity. The models were only validated for hips with normal morphology [20]. A version of this chapter will be submitted for publication. Given, L., Gilbart, M. and Wilson, D. (2010) Effect of cam-tye femoroacetabular impingement on hip kinematics.  58  In vivo studies of hip kinematics have shown that cam-lesions change hip motion patterns. In a study of level walking, patients with unilateral cam FAI had decreased abduction of the femur as well as decreased pelvic ROM compared to age-matched controls [8]. In a study of hip motions during maximum squat, patients with cam FAI had decreased maximum squat depth and pelvic recline compared to age matched controls [10].  It is, however, still unclear whether these  changes in kinematics were caused by compensatory muscle activity due to pain or by direct impingement of the lesion with the acetabulum. It is also unclear whether the center of rotation (COR) of the hip shifted during activity in patients with cam FAI because skin motion artifact makes it difficult to make these measurements with sufficient accuracy. Complete and sound biomechanical justification for surgical treatment of cam FAI has not yet been established. Osteochondroplasy, or resection of the cam deformity, can be performed as open or arthroscopic procedures. It is, however, not clear how large a cam lesion must be to alter joint mechanics and warrant surgical correction. Current guidelines for osteochondroplasty suggest overcorrection of the cam lesion, and it is not clear how such overcorrection affects hip mechanics. Biomechanical changes that are relevant to cam deformity are likely reflected in movement of the hip`s COR, altered patterns of coupled rotation and changes in the force required to achieve hip rotations. Direct contact between the deformity and acetabular rim would translate the COR of the hip away from the center of the acetabulum. Contact would also alter the rotations coupled to applied flexion and abduction. Continued rotation in the presence of such a deformity would likely require more muscle force than for an undeformed hip. Ideally, we would measure stress in the acetabular labrum and hip cartilage, but such measurements are difficult to make in the intact hip.  59  The objective of the present study was to answer the research question How do cam FAI lesions and resection osteochondroplasty affect patterns of hip rotation, translation of the center of femoral rotation and the force required to flex and abduct the hip in six cadaveric hemi-pelves flexed and abducted with simulated muscle loads?  2.2 Materials and methods 2.2.1 Specimen preparation Six cadaver hip specimens (including the hemi-pelvis and proximal femur sectioned midshaft) from five donors were prepared for testing. The donors included three males (two right, one left) and two females (two right, one left), were between the ages of 73 and 84 at the time of death (mean 79.2 years of age) and weighed between 58.5kg and 107.5kgs (mean, 72.3kgs). Specimens with a history of hip surgery were excluded from this study. Specimens were procured immediately following the donor’s death and were stored at -13°C until three days prior to testing at which time each was thawed at room temperature. All soft tissues were removed to the level of the joint capsule with the exception of the entire length of the distal tendons of the iliacus, gluteus maximus, gluteus medius and adductor magnus. Steel cables were attached to each of these distal tendons using sutures. Eyebolts were placed at the center of the site of proximal attachment for these same four muscles. The sacro-iliac joint was potted in dental stone to allow attachment of the pelvis to the Dynamic Hip Motion Simulator (DHMS).  2.2.2 Deformity simulation Three cam deformities of varying severity were simulated for each specimen using polymethyl-methacrylate (PMMA) bone cement with added barium sulphate to increase  60  radiodensity. The antero-superior region of the joint capsule was opened to allow access to the femoral head and neck and deformities were molded by hand and adjusted using a grinder when hardened to represent the geometry of natural cam lesions (Figure 2-1), which was confirmed by an experienced hip arthroscopy surgeon (MKG). A metal plug was inserted into the femoral neck which allowed a bolt to hold each deformity in place.  A  B  Figure 2-1: A) Hemi-pelvis specimen with open joint capsule and no simulated deformity. B) Same specimen with simulated deformity (arrow).  2.2.3 Dynamic hip motion simulator (DHMS) Flexion and abduction driven by simulated muscle shortening was applied to each specimen using the DHMS. Specimens were attached to the DHMS via an attachment plate which allowed rotation about two axes, allowing rotation of the pelvis into a neutral upright position, described below.  The cables attached to the tendons were run through the eyebolts at their proximal  attachments and then through pulleys to either a static load or a brushed servo-motor (Figure  61  2-2). To flex the hip, the iliacus was shortened with the motor while the gluteus medius and adductor magnus were statically loaded with 11N each resulting in flexion at a rate of approximately 1.4°/s. To abduct the hip, the gluteus medius was shortened while the iliacus and gluteus maximus were statically loaded with 11N each resulting in abduction at a rate of approximately 0.9°/s. The static load was chosen because it was the force required to keep the femoral head firmly in the acetabulum, while still allowing easy manipulation of the femur. The motors which shortened the simulated muscles were controlled by a custom program (Labview™, National Instruments, Austin TX) which increased the voltage to the motor, thereby increasing the torque produced by the motor, until a force of 156N was reached in the cable as measured by an inline S-type load cell (Hoskins Scientific, Vancouver BC), at which point the motor was turned off. Further details regarding the DHMS are provided in Appendix C.  Figure 2-2: Loading schematic. Red lines represent cables, blue dots represent eyebolts. The eyebolt associated with the gluteus maximus is hidden by the iliac wing in this view. 62  2.2.4 Experimental procedures Each specimen was positioned in the DHMS such that the ischial spine and superior pubic symphysis were aligned in the horizontal plane and the pubic symphysis was aligned in the sagittal plane. To place the femur in a neutral position, static loads of 11N were applied to each of the four tendon cables, and the femur was manually manipulated into neutral position (shaft adducted approximately 20°, shaft aligned in coronal plane, linea aspera directly posterior). Once the femur was in the neutral position, laser pointers which pointed at the femoral shaft were rigidly affixed to the DHMS and white paint was used to make markings at the two points where the lasers struck the femur. This enabled repeatable positioning of the femur in the neutral position at the start of each test sequence. With the femur in the neutral position, four bony landmarks on the pelvis (ASIS, superior pubic symphysis, inferior pubic symphysis and ischial spine) and three landmarks on the femur (anterior most point of the greater trochanter, inferior most point of the greater trochanter and lesser trochanter) were digitized using an Optotrak Certus (Northen Digital, Waterloo, ON, Canada, accuracy ±0.1mm, repeatability ±0.01mm) to create the pelvic and femoral coordinate frames. Movement of the hip was measured for five different states of each specimen: native, with each of the three simulated deformities, and after a resection osteochondroplasty.  Each  experimental condition was repeated three times and the order of testing was randomized for each specimen.  First, hip movement was measured for eight experimental conditions: flexion  and abduction with the native specimen and with each of the three deformity conditions for a total of 24 trials. Then, the specimen was removed from the DHMS, the simulated deformity was removed, and a resection osteochondroplasty was performed by an experienced hip  63  arthroscopy surgeon (MKG). The specimen was replaced in the DHMS and repositioned using the laser pointers. The same seven bony landmarks were digitized and six further motion trials (three flexion, three abduction) were performed in a randomized order for a total of 30 motion trials.  2.2.5 Kinematic procedures The positions of the femur and pelvis were tracked during applied flexion and abduction. A cluster of three optoelectronic markers was rigidly affixed to the iliac wing of the pelvis while two clusters of three markers (six total) were rigidly affixed to the femoral shaft. The position of each of these markers was tracked using the Optotrak Certus. The Optotrak sensor head was located such that all pelvic markers and a minimum of three femoral markers were visible at all times throughout the entire ROM of the femur. The Optotrak was triggered to start collecting by the same custom Labview™ program used to collect force data to allow for synchronization of kinematic and force data. The COR of the femur was used as the origin of the pelvic and femoral coordinate systems. This point was determined using a least squares sphere fitting algorithm each marker during each of the three flexion and three abduction trials in the native condition. The average center of rotation of each of the six markers and six trials was used as the origin for the native and three deformity conditions. This process was repeated using the resected condition, allowing this condition to have a different origin in case of any difference between the position of the specimen before performing the resection and after. The axes of the pelvic coordinate system were defined such that the pubic symphysis and ASIS were aligned in the coronal plane, the pubic symphysis was aligned in the sagittal plane  64  and the ischial spine and superior pubic symphysis were aligned in the horizontal plane. Since only the proximal femur was used, it was not possible to determine the femoral coordinate system using bony landmarks. Instead the femoral coordinate system was defined as being aligned with the pelvic coordinate system when the femur was in neutral alignment. Motion was applied at an average rate of 1.4°/s during flexion and 0.9°/s during abduction, and data were acquired 20Hz. For each position data point, flexion, abduction and internal rotation angles and translation of the femur were determined using the floating axis system [4]. Linear interpolation was performed to determine the abduction angle, internal rotation angle, translation of the COR of the femur and force on the cable representing the iliacus muscle at each degree of flexion during flexion trials and to determine the flexion angle, internal rotation angle, translation of the COR of the femur and force on the cable representing the gluteus medius muscle at each degree of abduction during abduction trials.  2.2.6 Imaging and morphological measurements The alpha angle was measured for each of the five conditions. A three dimensional image of each specimen in each of the five deformity conditions was acquired using an isocentric C-Arm Fluoroscope (Arcadis Orbic, Siemens, Berlin Germany). Using Analyze™, radial slices were made at five degree increments about the femoral neck axis from superior to anterior allowing for measurements to be made across the entire anterior-superior quadrant of the femoral headneck. On each slice, the alpha angle [14] was measured using a custom Matlab™ program. Each measurement was repeated three times in a randomized order and the average of the three measurements was used.  65  2.2.7 Sources of funding Funding for this project was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Arthritis Network (CAN) and Michael Smith Foundation for Health Research (MSFHR).  2.3 Statistical methods Specimens and deformities were grouped into four categories of deformity severity based on the maximum alpha angle over the antero-superior region: “No Deformity” (maximum alpha angle less than 50°); “Minor Deformity” (maximum alpha angle between 50° and 70°); “Moderate Deformity” (maximum alpha angle between 70° and 85°), and “Severe Deformity” (maximum alpha angle greater than 85°). Linear mixed models were used to determine differences between deformity severities according to Equation 2-1 where M is the measurement of interest (out-of-plane motion, translation or required force), Angle is the angle of flexion for flexion trials or the angle of abduction for abduction trials. A is the intercept and AID is the change in intercept due to deformity, B is the slope and BID is the change in slope due to deformity, C is the rate of change of the slope and DSpecimen is the random effect due to the specimen. This model assumes that while the intercept and slope may vary due to deformity, the rate of change of the slope will not vary. To compare only the native and resected conditions, a new model was employed which followed the same form using new coefficients.  Equation 2-1  66  The total system accuracy was determined by the sum of the accuracy of determining the coordinate system, the accuracy of tracking the markers and the accuracy of the calculations [21].  2.4 Results 2.4.1 Accuracy and repeatability of the DHMS The RMS error across 3 cycles was smaller than the error of the system. It was determined that the total system accuracy was within a 95% confidence of 2.6mm and 5.9° (Appendix D). For the repeated trials of the six specimens, during prescribed flexion, there was an average standard deviation between trials of 2.11° (sd 1.87°) in the abduction angle, 1.39° (sd 1.21°) in the internal rotation angle, 0.51mm (sd 0.74mm) in the translation of the COR and 9.16N (sd 7.16N) in the force required to create the motion. During prescribed abduction, there was an average standard deviation between trials of 1.17° (sd 0.93°) in the flexion angle, 1.45° (sd 1.20°) in the internal rotation angle, 0.97mm (sd 1.52mm) in the translation of the COR and 10.72N (sd 10.94N) in the force required to create the motion.  2.4.2 Changes in kinematics due to deformity severity 2.4.2.1 Prescribed flexion A cam deformity caused decreased internal rotation and abduction with flexion, with the exception of the minor deformity which resulted in increased abduction (Figure 2-3, Figure 2-4 and Figure 2-5). In the hip with no deformity, the femur first abducted and internally rotated slightly until approximately 20° of flexion, then adducted and continued to internally rotate for the rest of the range of flexion. Every deformity size caused statistically significant differences  67  in patters on abduction and internal rotation from the no deformity case (Table 2-1). A minor deformity resulted in a decrease of 0.087° internal rotation and an increase of 0.089° abduction for each degree of prescribed flexion compared to no deformity. A moderate deformity caused a decrease of 0.205° internal rotation and 0.135° abduction per degree flexion and a severe deformity caused a decrease of 0.479° internal rotation and 0.315° abduction per degree flexion when compared to no deformity.  Figure 2-3: Raw motion data for internal rotation as a function of prescribed flexion in all flexion trials for one specimen.  68  Figure 2-4: Mean profile for internal rotation of the femur during prescribed flexion.  Figure 2-5: Mean profile for abduction of the femur during prescribed flexion.  Cam deformity increased the muscle force required to flex the hip (Figure 2-6, Table 2-1). In general, the required force increased with flexion. Statistically significant differences were 69  observed between all levels of deformity. In the hip with no deformity, a force of approximately 100N was required to flex the hip to 70°. This force requirement was more than doubled with a severe deformity, with the difference between the force requirements for the impingement free hip and a hip with cam deformity increasing throughout flexion.  Figure 2-6: Mean profile for the force required to create prescribed flexion.  70  Measurement  Internal Rotation (deg)  Deformity Condition  Minor  Moderate  Severe  Abduction (deg)  Minor  Moderate  Severe  Force (N)  Minor  Moderate  Severe  Compared deformity condition Intercept No Minor Moderate Deformity 2.27 p<0.001 1.45 to 3.09 1.79 -0.48 p<0.001 p=0.199 1.05:2.53 -1.22 to 0.25 0.17 -2.10 -1.62 p=0.634 p<0.001 p<0.001 -0.54 to -2.88 to -2.37 to 0.89 1.32 0.87 -4.27 p<0.001 -5.09 to 3.45 -1.41 2.26 p<0.001 p<0.001 -2.14 to 2.13 to 3.59 0.67 -2.21 2.06 -0.80 p<0.001 p<0.001 p=0.036 -2.92 to 1.28 to 2.84 -1.55 to 1.49 0.05 6.38 p<0.001 2.95 to 9.80 -9.31 -15.69 p<0.001 p<0.001 -12.38 to -18.76 to 6.25 12.63 -8.62 -15.00 0.69 p<0.001 p<0.001 p=0.663 -11.62 to -18.25 to -2.42 to 5.62 11.75 3.80  Compared deformity condition - Slope No Deformity -0.087 p<0.001 -0.107 to 0.066 -0.205 p<0.001 -0.224 to 0.185 -0.479 p<0.001 -0.499 to 0.459 0.089 p<0.001 0.068 to 0.110 -0.135 p<0.001 -0.155 to 0.115 -0.315 p<0.001 -0.335 to 0.295 0.248 p<0.001 0.161 to 0.335 1.369 p<0.001 1.286 to 1.452 1.946 p<0.001 1.861 to 2.031  Minor  Moderate  -0.118 p<0.001 -0.138 to 0.098 -0.392 p<0.001 -0.414 to 0.371  -0.275 p<0.001 -0.296 to 0.253  2.859 p<0.001 2.127 to 3.591 2.061 p<0.001 1.283 to 2.838  -0.799 p=0.036 -1.546 to 0.051  1.121 p<0.001 1.037 to 1.205 1.698 p<0.001 1.607 to 1.789  0.577 p<0.001 0.486 to 0.667  Table 2-1: Changes in intercept and slope for the mean profiles of internal rotation, abduction and force during prescribed flexion due to deformity severity. Coefficients, p-values and confidence intervals provided.  During prescribed flexion, cam deformity caused increased total translation of the COR of the femur throughout the range of flexion (Figure 2-7,  71  ).  No significant difference was found between no deformity and minor deformity or  between moderate deformity and severe deformity; however, differences were found between no deformity and moderate deformity and between no deformity and severe deformity. In the hip with no deformity, the COR translated by approximately 5mm throughout the range of flexion. This increased to approximately 6.5mm with a severe deformity. The COR of the femur first translated posteriorly, then anteriorly (Figure 2-8).  It translated inferiorly and laterally  throughout the full range of motion (Figure 2-9, Figure 2-10). Though significant differences were found in the amount of translation between deformity groups in all three directions, no consistent trends were observed with increasing deformity severity.  Figure 2-7: Mean profile for Euclidean translation of the COR of the femur during prescribed flexion.  72  Figure 2-8: Mean profile for translation of the COR of the femur along the X-axis during prescribed flexion. Translation in the positive X-direction corresponds to translation in the anterior direction.  Figure 2-9: Mean profile for translation of the COR of the femur along the Y-axis during prescribed flexion. Translation in the positive Y-direction corresponds to translation in the proximal direction.  73  Figure 2-10: Mean profile for translation of the COR of the femur along the Z-axis during prescribed flexion. Translation in the positive Z-direction corresponds to translation in the lateral direction.  Table 2-2: Changes in intercept and slope for the direction of translation for the mean profiles during prescribed flexion due to deformity severity. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially (next page).  74  Measurement  Euclidean translation (mm)  Deformity Condition  Minor  Moderate  Severe  Translation along X-axis (mm)  Minor  Moderate  Severe  Translation along Y-axis (mm)  Minor  Moderate  Severe  Translation along Z-axis (mm)  Minor  Moderate  Severe  Compared deformity condition Intercept No Minor Moderate Deformity -0.94 p<0.001 -1.21 to 0.68 -1.97 -1.03 p<0.001 p<0.001 -2.21 to -1.27 to 1.73 0.79 -1.36 -0.42 0.61 p<0.001 p=0.001 p<0.001 -1.59 to -0.67 to 0.37 to 1.13 0.17 0.85 1.05 P<0.001 0.79 to 1.32 1.68 0.62 P<0.001 P<0.001 1.43 to 0.38 to 0.86 1.92 0.74 -0.32 -0.94 P<0.001 P=0.013 P<0.001 0.51 to -0.57 to -1.18 to 0.97 0.07 0.70 1.03 P<0.001 0.72 to 1.34 1.60 0.58 P<0.001 P<0.001 1.32 to 0.30 to 0.86 1.89 0.55 -0.48 -1.06 P<0.001 P=0.001 P<0.001 0.28 to -0.77 to -1.33 to 0.82 0.19 0.78 0.28 P=0.067 -0.019 to 0.58 0.52 0.24 P<0.001 P=0.081 0.24 to -0.03 to 0.79 0.50 0.50 0.22 -0.01 P<0.001 P=0.116 P=0.929 0.24 to -0.05 to -0.28 to 0.76 0.50 0.26  75  Compared deformity condition - Slope No Deformity 0.005 p=0.117 -0.001 to 0.012 0.013 p<0.001 0.007 to 0.020 0.016 p<0.001 0.009 to 0.023 -0.025 P<0.001 -0.032 to 0.018 -0.026 P<0.001 -0.032 to 0.019 -0.002 P=0.599 -0.008 to 0.005 0.023 P<0.001 0.015 to 0.031 0.009 P=0.025 0.001 to 0.016 0.008 P=0.054 -0.000 to 0.015 0.001 P=0.711 -0.006 to 0.009 -0.002 P=0.503 -0.010 to 0.005 -0.009 P=0.12 -0.017 to 0.002  Minor  Moderate  0.008 p=0.017 0.001 to 0.014 0.011 p=0.003 0.003 to 0.018  0.003 p=0.470 -0.004 to 0.010  -0.001 P=0.805 -0.007 to 0.006 0.023 P<0.001 0.016 to 0.030  0.024 P<0.001 0.017 to 0.031  -0.014 P<0.001 -0.022 to 0.007 -0.016 P<0.001 -0.024 to 0.007  -0.001 P=0.793 -0.009 to 0.007  -0.004 P=0.290 -0.011 to 0.003 -0.011 P=0.007 -0.019 to 0.003  -0.007 P=0.082 -0.015 to 0.001  2.4.2.2 Prescribed abduction A cam deformity caused increased internal rotation and decreased flexion with abduction (Figure 2-11 and Figure 2-12, Table 2-3). In the hip with no deformity, the femur externally rotated and flexed until approximately 10° of abduction, then internally rotated and continued to flex throughout the range of abduction. Every deformity size caused statistically significant differences in the patterns of internal rotation.  Moderate and severe deformity caused  statistically significant differences in the patterns of flexion compared to no deformity; however, no difference was observed in the pattern of flexion during prescribed abduction between no deformity and minor deformity. A minor cam deformity resulted in an increase of 0.124° internal rotation per degree abduction compared to no deformity. A moderate deformity caused an increase of 0.093° internal rotation and a decrease of 0.089° flexion and a severe deformity caused an increase of 0.231° internal rotation and a decrease of 0.243° flexion per degree abduction compared to no deformity. No significant difference was observed in the amount of flexion per degree abduction between the no deformity and minor deformity conditions.  76  Figure 2-11: Mean profile for internal rotation of the femur during prescribed abduction.  Figure 2-12: Mean profile for flexion of the femur during prescribed abduction.  Cam deformity increased the muscle force required to abduct the hip (Figure 2-13, Table 2-3). Statistically significant increases in the required force were observed for all levels of  77  deformity compared to the no deformity hip. In general, the required force increased with abduction. In the hip with no deformity, a force of approximately 100N was required to abduct the hip to 35°. In a hip with a severe simulated deformity, this force increased to approximately 150N, with the difference between the force requirements for the impingement free hip and a hip with cam deformity increasing throughout abduction.  Figure 2-13: Mean profile for the force required to create prescribed abduction.  78  Measurement  Deformity Condition  Internal Rotation (deg)  Minor  Moderate  Severe  Flexion (deg)  Minor  Moderate  Severe  Force (N)  Minor  Moderate  Severe  Compared deformity condition Intercept No Minor Moderate Deformity -1.37 p<0.001 -2.02 to 0.71 -2.06 -0.69 p<0.001 p=0.020 -2.64 to -1.27 to 1.47 0.11 -8.59 -7.23 6.54 p<0.001 p<0.001 p<0.001 -9.15 to -7.81 to -7.09 to 8.03 6.64 5.98 -0.82 p=0.013 -1.46 to 0.17 1.43 2.24 p<0.001 p<0.001 0.85 to 1.67 to 2.00 2.82 3.32 4.14 1.90 p<0.001 p<0.001 p<0.001 2.78 to 3.57 to 1.36 to 3.87 4.71 2.44 4.32 p=0.149 -1.55 to 10.18 2.78 -1.54 p=304 p=0.563 -2.52 to -6.75 to 8.08 3.68 5.41 1.09 2.63 p=0.035 p=0.679 p=0.288 0.38 to -4.07 to -2.22 to 10.43 6.25 7.58  Compared deformity condition Slope No Minor Moderate Deformity 0.124 p<0.001 0.092 to 0.155 0.093 -0.030 p<0.001 p=0.045 0.063 to -0.060 to 0.123 0.001 0.231 0.107 0.138 p<0.001 p<0001 p<0.001 0.197 to 0.073 to 0.103 to 0.265 0.142 0.172 0.019 p=0.243 -0.013 to 0.050 -0.089 -0.108 p<0.001 p<0.001 -0.119 to -0.137 to 0.060 0.079 -0.243 -0.261 -0.153 p<0.001 p<0.001 p<0.001 -0.276 to -0.295 to - -0.187 to 0.210 0.227 0.120 0.393 p=0.006 0.110 to 0.677 0.560 0.166 p<0.001 p=0.219 0.291 to -0.099 to 0.829 0.431 1.645 1.251 1.09 p<0.001 p<0.001 p<0.001 1.343 to 0.945 to 0.783 to 1.947 1.557 1.387  Table 2-3: Change in intercept and slope in the mean profiles during prescribed abduction due to deformity severity. Coefficients, p-values and confidence intervals provided.  During prescribed abduction, a cam deformity caused decreased total translation of the COR of the femur throughout the range of abduction (Figure 2-14,  79  Table 2-4). Statistically significant differences in the pattern of translation during abduction were found for moderate and severe deformity compared to no deformity but no difference was observed between minor deformity and no deformity. In the hip with no deformity, the COR translated by approximately 5.5mm.  This decreased to approximately 4.5mm with severe  deformity. During prescribed abduction, the COR of the femoral head translatied posteriorly, inferiorly and medially (Figure 2-15, Figure 2-16 and Figure 2-17). Again, though significant differences were found in the amount of translation between deformity groups in all three directions, no consistent trends were observed with increasing deformity severity.  Figure 2-14: Mean profile for Euclidean translation of the COR of the femur during prescribed abduction.  80  Figure 2-15: Mean profile for translation of the COR of the femur along the X-axis during prescribed abduction. Translation in the positive X-direction corresponds to translation in the anterior direction.  Figure 2-16: Mean profile for translation of the COR of the femur along the Y-axis during prescribed abduction. Translation in the positive Y-direction corresponds to translation in the proximal direction.  81  Figure 2-17: Mean profile for translation of the COR of the femur along the Z-axis during prescribed abduction. Translation in the positive Z-direction corresponds to translation in the lateral direction.  Table 2-4: Changes in intercept and slope for the direction of translation for the mean profiles during prescribed abduction due to deformity severity. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially.  82  Measurement  Deformity Condition  Euclidean Translation (mm)  Minor  Moderate  Severe  Translation along X-axis (mm)  Minor  Moderate  Severe  Translation along Y-axis (mm)  Minor  Moderate  Severe  Translation along Z-axis (mm)  Minor  Moderate  Severe  Compared deformity condition Intercept No Minor Moderate Deformity -0.40 p=0.233 -1.05 to 0.25 1.12 1.52 p<0.001 p<0.001 0.52 to 0.95 to 1.73 2.09 1.58 1.98 0.46 p<0.001 p<0.001 p=0.100 1.03 to 1.41 to -0.09 to 2.14 2.54 1.00 0.67 P=0.009 0.17 to 1.17 0.67 0.00 P=0.005 P=0.999 0.21 to -0.43 to 1.13 0.44 0.35 -0.32 -0.32 P=0.112 P=0.146 P=0.120 -0.08 to -0.75 to -0.72 to 0.78 0.11 0.08 0.11 P=0.505 -0.21 to 0.44 -0.01 -0.12 P=0.972 P=0.422 -0.30 to -0.40 to 0.29 0.17 -0.76 -0.87 -0.76 P<0.001 P<0.001 P<0.001 -1.04 to -1.15 -1.01 to 0.48 -0.59 0.50 0.81 P=0.002 0.30 to 1.32 1.15 0.34 P<0.001 P=0.136 0.67 to -0.11 to 1.63 0.79 0.35 -0.46 -0.80 P=0.114 P=0.043 P<0.001 -0.08 to -0.90 to -1.22 to 0.79 0.01 0.37  83  Compared deformity condition Slope No Minor Moderate Deformity 0.009 p=0.574 -0.022 to 0.040 -0.044 -0.053 p=0.005 p<0.001 -0.075 to -0.082 to 0.013 0.024 -0.037 -0.046 0.007 p=0.029 p=0.007 p=0.685 -0.070 to -0.079 to - -0.027 to 0.004 0.013 0.040 -0.052 P<0.001 -0.076 to 0.028 -0.084 -0.032 P<0.001 P=0.005 -0.108 to -0.055 to 0.061 0.010 -0.053 -0.001 0.031 P<0.001 P=0.916 P=0.016 -0.079 to -0.027 to 0.006 to 0.027 0.024 0.057 0.025 P=0.002 0.010 to 0.041 0.018 -0.007 P=0.018 P=0.328 0.003 to -0.022 to 0.033 0.007 0.019 -0.007 0.00 P=0.030 P=0.428 P=0.955 0.002 to -0.024 to -0.016 to 0.036 0.010 0.017 -0.071 P<0.001 -0.096 to 0.047 -0.108 -0.037 P<0.001 P=0.002 -0.132 to -0.060 to 0.084 0.014 -0.059 0.012 0.049 P<0.001 P=0.363 P<0.001 -0.085 to -0.14 to 0.023 to 0.033 0.038 0.075  2.4.3 Changes in kinematics due to resection osteochondroplasty Resection osteochondroplasty caused increased internal rotation during prescribed flexion and reduced the force required to create flexion (Figure 2-18 and Figure 2-20, Table 2-5). No significant difference was observed in the angle of abduction during prescribed flexion between the native and resected conditions (Figure 2-19).  Figure 2-18: Mean profile for internal rotation of the femur during prescribed flexion comparison of the native and resected conditions.  84  Figure 2-19: Mean profile for abduction of the femur during prescribed flexion - comparison of the native and resected conditions.  Figure 2-20: Mean profile for the force required to create prescribed flexion - comparison of the native and resected conditions.  85  Measurement Internal Rotation (deg) Abduction (deg) Force (N)  Resected compared to native Intercept  Slope  0.59 p=0.001 0.25 to 0.92 1.61 p<0.001 1.11 to 2.12 3.49 p<0.001 1.70 to 5.28  0.039 p<0.001 0.030 to 0.048 0.005 p=0.479 -0.009 to 0.183 -0.399 p< 0.001 -0.447 to 0.352  Table 2-5: Changes in intercept and slope for the mean profiles during prescribed flexion due to resection. Coefficients, p-values and confidence intervals provided.  Resection osteochondroplasty resulted in increased total translation of the COR of the femur during prescribed flexion (Figure 2-21, Table 2-6). Translation was increased both anteriorly and inferiorly with resection osteochondroplasty (Figure 2-22 and Figure 2-23). No significant difference was found in the amount of medial-lateral translation (Figure 2-24).  Figure 2-21: Mean profile for Euclidean translation of the COR of the femur during prescribed flexion - comparison of native and resected conditions  86  Figure 2-22: Mean profile for translation of the COR of the femur along the X-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive Xdirection corresponds to translation in the anterior direction.  Figure 2-23: Mean profile for translation of the COR of the femur along the Y-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive Ydirection corresponds to translation in the proximal direction.  87  Figure 2-24: Mean profile for translation of the COR of the femur along the Z-axis during prescribed flexion – comparison of native and resected conditions. Translation in the positive Zdirection corresponds to translation in the lateral direction.  Measurement Euclidean translation (mm) Translation along X-axis (mm) Translation along Y-axis (mm) Translation along Z-axis (mm)  Resected compared to native Intercept  Slope  0.93 p<0.001 0.73 to 1.13 -0.61 P<0.001 -0.76 to 0.47 0.14 P=0.265 -0.11 to 0.40 -0.21 P=0.063 -0.44 to 0.01  0.012 p<0.001 0.007 to 0.018 0.024 P<0.001 0.020 to 0.028 -0.044 P<0.001 -0.051 to 0.039 -0.004 P=0.142 -0.010 to 0.001  Table 2-6: Changes in intercept and slope of the direction of translation for the mean profiles during prescribed flexion due to resection. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially.  88  Resection osteochondroplasty caused decreased internal rotation during prescribed abduction (Figure 2-25, Table 2-7). No significant difference was observed in the flexion angle force required to create abduction (Figure 2-26 and Figure 2-27, Table 2-7).  Figure 2-25: Mean profile for internal rotation of the femur during prescribed abduction comparison of the native and resected conditions.  89  Figure 2-26: Mean profile for flexion of the femur during prescribed abduction - comparison of the native and resected conditions.  Figure 2-27: Mean profile for force required to create prescribed abduction - comparison of the native and resected conditions.  90  Measurement  Resected compared to native Intercept  Slope  Internal Rotation (deg)  2.37 p<0.001 1.85 to 2.89  Flexion (deg)  0.63 p=0.024 0.08 to 1.18 -2.29 p=0.268 -6.34 to 1.76  -0.115 p<0.001 -0.141 to 0.089 -0.020 p=0.158 -0.047 to 0.008 -0.155 p=0.131 -0.357 to 0.046  Force (N)  Table 2-7: Changes in intercept and slope for the mean profiles during abduction due to resection. Coefficients, p-values and confidence intervals provided.  No significant difference was observed in the total translation of the COR of the femur during prescribed abduction (Figure 2-28, Table 2-8). When this translation was broken down into the three directions, it was found that increased translation did occur inferiorly after resection (Figure 2-30). No significant difference was observed in the amount of anteriorposterior or medial-lateral translation (Figure 2-29 and Figure 2-31).  Figure 2-28: Mean profile for Euclidean translation of the COR of the femur during prescribed abduction - comparison of the native and resected conditions.  91  Figure 2-29: Mean profile for translation of the COR of the femur along the X-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive X-direction corresponds to translation in the anterior direction.  Figure 2-30: Mean profile for translation of the COR of the femur along the Y-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive Y-direction corresponds to translation in the proximal direction.  92  Figure 2-31: Mean profile for translation of the COR of the femur along the Z-axis during prescribed abduction – comparison of native and resected conditions. Translation in the positive Z-direction corresponds to translation in the lateral direction.  Measurement  Resected compared to native Intercept  Slope  Euclidean translation (mm) Translation along X-axis (mm) Translation along Y-axis (mm)  0.08 p=0.619 -0.24 to 0.40 0.09 P=0.383 -0.11 to 0.28 0.26 P=0.015 0.05 to 0.48  Translation along Z-axis (mm)  0.26 P=0.027 0.03 to 0.48  0.011 p=0.164 -0.005 to 0.027 0.007 P=0.140 -0.002 to 0.017 -0.042 P<0.001 -0.053 to 0.032 -0.013 P=0.028 -0.024 to 0.001  Table 2-8: Changes in intercept and slope of the direction of translation for the mean profiles during prescribed abduction due to resection. Coefficients, p-values and confidence intervals provided. Positive translation along the X-axis corresponds to translation anteriorly, positive translation along the Y-axis corresponds to translation superiorly and positive translation along the Z-axis corresponds to translation medially.  93  2.5 Discussion We compared out-of-plane motions, translations and muscle forces during active unconstrained flexion and abduction of the hip in six cadavers under native and simulated deformity conditions as well as following resection osteochondroplasty. We found that during prescribed flexion, increased adduction, external rotation and translation of the hip joint center occurred with increased deformity severity. During prescribed abduction, increased extension and internal rotation and decreased translation were observed with increased deformity severity. More muscle force was required to create both flexion and abduction with increased deformity severity. The findings of this study suggest that substantially different loading environments are present in the articular contact regions of normal hips compared to hips with cam lesions throughout a range of motion common in everyday life. Changes in the rotations coupled to prescribed flexion and abduction must be due to altered contact geometry at the hip since this was the only change created between states of the hip.  These changes were especially  pronounced in moderate and severe deformities throughout the entire range of motion. The increased force required to create both flexion and abduction with increasing deformity size suggests an increase in the total forces acting across the joint and an increase in soft tissue forces. It is possible that some of this change in required force is due to the change in the COR. The change in rotational center between normal and severely deformed hips is approximately 1.3mm (change in translation of 1.5mm over 70° of flexion). This would require an increase in force of the dynamic load of approximately 3% of the original dynamic load plus 3% of the equivalent static load if the moment arm of both was originally 5cm. It is, therefore, impossible for the entire increase in force of over 100% of the original dynamic load to be a result of the change in  94  rotational center. It is more likely that the change in required force is due to a change in joint forces. In the hip with no deformity, joint forces acting perpendicular to the surface are the femur are approximately coincident with the center of the femur, therefore not creating moments. In a hip with cam FAI, the forces will still be acting perpendicular to the joint surface; however, they will not intersect at the center of the femoral hip and therefore will create moments about the center of rotation. To overcome these moments, a higher muscle force would be required to create flexion or abduction. While it is unclear at this time whether or not the changes to out-ofplane motions would be found in weightbearing, it is likely that the increase in force required to create flexion and abduction would be. In weightbearing, the joint forces would be much higher and, therefore, the moments produced within the joint would be higher, requiring even more muscle force to create the desired motion. Translation of the COR of the femur suggests that movement of the hip is not simply constrained by the spherical surfaces of the femur and acetabulum. Translation in the hip joint may be the result of distraction of the femur at the point of impingement. When impingement occurs, further motion requires a prying of the femoral head from the acetabulum, resulting in translation of the COR of the femur. The observed increase in translation in the resected condition during prescribed flexion when compared to the native condition may have been due to increased joint laxity occurring intraoperatively. During the surgery, the femoral head was partially distracted from the acetabulum. This may have resulted in stretching of the ligamentum teres as well as the joint capsule and ligaments. This increased laxity may have allowed for more subluxation during motion than prior to surgery.  This finding would not be expected in vivo since the joint capsule and  ligaments would be able to heal. Other observed differences between the native and resected  95  conditions, such as the increased internal rotation during flexion and increased external rotation during abduction, followed the same patterns as observed between varying deformity severities and are, therefore, likely the result of decreased abutment between the femoral head-neck region and the acetabulum. This implies that resection osteochondroplasty, while altering hip joint kinematics, is successful in limiting the contact in the impingement zone. Our finding of increased external rotation with flexion has been previously reported. Rab (1999) simulated walking in SCFE patients. It was reported that at heel strike, approximately 40° flexion, a hip with moderate SCFE (posterior slip angle = 50°) was externally rotated by approximately 25° compared to a normal hip [16]. In the present study, it was found that at 40° flexion in a hip with a severe cam lesion, the hip was externally rotated approximately 20° more than a hip with no deformity. Further, our finding of increased hip adduction during flexion for moderate and severe deformities supports the findings of Kennedy et al. (2009) who observed increased hip adduction during the swing phase of gait [8]. We found that at 40° flexion (approximate heel strike), a hip with severe deformity was adducted approximately 12° more than a hip with no deformity. Kennedy et al. (2009) observed an increase in adduction of approximately 3° at 40° flexion in the patient group compared to controls, however no distinction was made between varying severities of deformity and the patient group was defined only by having an alpha angle greater than 50.5° [8]. It is likely, therefore, that the patient group contained a combination of mild, moderate and severe deformities. Our findings show that severity of deformity affects the amount of adduction observed and that minor deformity (alpha angle between 50° and 70°) does not create increased adduction during flexion.  It is possible, therefore, that the small difference in adduction  observed in the above gait study is due to the inclusion of minor deformities as well as moderate  96  and severe deformities and it is speculated that if minor deformities were excluded from the study, a larger difference in adduction, such as the one that found in the present study, would be observed. This study had a number of strengths. The design of the study allowed for each specimen to be used as its own control, enabling the effect of deformities alone on kinematics to be determined. This study also used muscle actuation and muscle co-contraction to create motion in the hip joint. This is an important feature because it has been shown that the pelvis deforms under muscle loading, creating a different mechanical environment in the hip joint than a statically equivalent loading schema [1]. As well, a range of physiologically relevant deformity sizes was used allowing comparisons between severities of deformity. Further, a large ROM was simulated and measured in three dimensions, allowing for analysis of in-plane as well as out-ofplane motion. Finally, motion was tracked accurately enough to allow measurement of the small translations occurring within the hip joint. This study had inherent limitations that could not be avoided. The calculations used to determine the angles and translations rely on accurate determination of the joint COR and axes of the coordinate system. Presence of only the proximal femur meant that the standard femoral coordinate system could not be defined due to the lack of femoral epicondyles. As such, an alternate coordinate system was used which could have differed slightly from the standard coordinate system [23]. If, for example, the defined flexion axis was off from the true flexion axis by a 5° rotation about the abduction axis, a true 50° flexion would be represented by 49.8° flexion, 3.8° internal rotation and -1.8° abduction. As such, it is possible that some of the coupled motions are artifacts of the defined coordinate system; however, this artifact is only present when comparing the results to motions defined in the standard coordinate system and  97  differences observed between deformity groups in the present study must be due to deformity severity since the same coordinate system was used for all specimens and all deformity conditions within the specimen. Accurate determination of the hip joint center affected the calculated translations only, not rotations, since the hip joint center was determined independently of joint axes. Other limitations include the age of the specimens used, which increased the likelihood of OA and native deformities. It was noted by the participating hip arthroscopy surgeon (MKG) that one specimen had a large anterior osteophyte (maximum alpha angle = 75°) and another had a native cam lesion (maximum alpha angle = 79°). These native lesions, however, would not have affected the results of this study due to the method of grouping deformities for comparison: the native condition for both of these cases would have been considered moderate deformity rather than no deformity. Further limitations in this study are related to simulating the in vivo situation. These include limitations due to the nature of the manually created deformities. Care was taken to ensure that all deformities were as close to physiologic as possible and geometries were further confirmed by the participating hip arthroscopy surgeon; however, the transition from bone to simulated deformity may not have been as smooth as in vivo and it is possible that small motions between the deformity and the bone may have been present. Further, the motion simulated was active, unconstrained, non-weightbearing motion. This type of motion was chosen over weightbearing to simulate more closely the swing phase of gait and ROM studies, allowing for comparison of the results to previous findings. Finally, the motions created by the DHMS were done so by statically loading two tendons with equal loads while increasing the load on a third. It is likely that this loading scheme is not physiologically accurate; however, the data required to create  98  physiologically accurate motions are not available at this time. As described above, the patterns of coupled motion are similar to those previously reported; therefore it is likely that the motion paths were close to physiologic. In conclusion, the present study determined that joint mechanics are altered due to cam lesions throughout a wide range of motion, rather than just the extremes of motion, likely due to interactions between the deformity and soft tissues. As such, it is recommended that models of hip motion in cam FAI include soft tissues and that resection osteochondroplasty be considered rather than conservative treatments which advise only to avoid extreme motions.  99  2.6 References  1. Bay B, Hamel A, Olson S, Sharkey N. Statically equivalent load and support conditions produce different hip joint contact pressures and periacetabular strains. J Biomech. 1997;30:193196. 2. Beck M, Kalhor M, Leunig M, Ganz R. Hip morphology influences the pattern of damage to the acetabular cartilage: FAI as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br. 2005;87:1012-1018. 3. Bittersohl B, Steppacher S, Haamberg T, Kim Y, Werlen S, Beck M, Siebenrock K, Mamisch T. Cartilage damage in FAI (FAI): preliminary results on comparison of standard diagnostic vs delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC). Osteoarthritis Cartilage. 2009. 4. Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock K. FAI: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003:112-120. 5. Grood E, Suntay W. A joint coordinate system for the clinical description of threedimensional motions: application to the knee. J Biomech Eng. 1983;105:136-144. 6. Ito K, Minka Mn, Leunig M, Werlen S, Ganz R. FAI and the cam-effect. A MRI-based quantitative anatomical study of the femoral head-neck offset. J Bone Joint Surg Br. 2001;83:171-176. 7. Johnston T, Schenker M, Briggs K, Philippon M. Relationship between offset angle alpha and hip chondral injury in FAI. Arthroscopy. 2008;24:669-675. 8. Kennedy M, Lamontagne M, Beaulé P. FAI alters hip and pelvic biomechanics during gait Walking biomechanics of FAI. Gait Posture. 2009;30:41-44. 9. Kubiak-Langer M, Tannast M, Murphy S, Siebenrock K, Langlotz F. Range of motion in anterior FAI. Clin Orthop Relat Res. 2007;458:117-124. 10. Lamontagne M, Kennedy M, Beaulé P. The effect of cam FAI on hip and pelvic motion during maximum squat. Clin Orthop Relat Res. 2009;467:645-650. 11. Lavigne M, Parvizi J, Beck M, Siebenrock K, Ganz R, Leunig M. Anterior FAI: part I. Techniques of joint preserving surgery. Clin Orthop Relat Res. 2004:61-66. 12. Leunig M, Beaulé P, Ganz R. The concept of FAI: current status and future perspectives. Clin Orthop Relat Res. 2009;467:616-622.  100  13. Leunig M, Casillas M, Hamlet M, Hersche O, Nötzli H, Slongo T, Ganz R. Slipped capital femoral epiphysis: early mechanical damage to the acetabular cartilage by a prominent femoral metaphysis. Acta Orthop Scand. 2000;71:370-375. 14. Mamisch T, Kim Y, Richolt J, Millis M, Kordelle J. Femoral morphology due to impingement influences the range of motion in slipped capital femoral epiphysis. Clin Orthop Relat Res. 2009;467:692-698. 15. Nötzli H, Wyss T, Stoecklin C, Schmid M, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br. 2002;84:556-560. 16. Rab G. The geometry of slipped capital femoral epiphysis: implications for movement, impingement, and corrective osteotomy. J Pediatr Orthop. 1999;19:419-424. 17. Richolt J, Teschner M, Everett P, Millis M, Kikinis R. Impingement simulation of the hip in SCFE using 3D models. Comput Aided Surg. 1999;4:144-151. 18. Snow S, Keret D, Scarangella S, Bowen J. Anterior impingement of the femoral head: a late phenomenon of Legg-Calvé-Perthes' disease. J Pediatr Orthop.13:286-289. 19. Tannast M, Goricki D, Beck M, Murphy S, Siebenrock K. Hip damage occurs at the zone of FAI. Clin Orthop Relat Res. 2008;466:273-280. 20. Tannast M, Kubiak-Langer M, Langlotz F, Puls M, Murphy S, Siebenrock K. Noninvasive three-dimensional assessment of FAI. J Orthop Res. 2007;25:122-131. 21. Taylor J. An Introduction to Error Analysis: The study of uncertainties in physical measurements. Sausalito, CA: University Science Books; 1982. 22. Wagner S, Hofstetter W, Chiquet M, Mainil-Varlet P, Stauffer E, Ganz R, Siebenrock K. Early osteoarthritic changes of human femoral head cartilage subsequent to femoro-acetabular impingement. Osteoarthritis Cartilage. 2003;11:508-518. 23. Wu G, Siegler S, Allard P, Kirtley C, Leardini A, Rosenbaum D, Whittle M, D'Lima D, Cristofolini L, Witte H, Schmid O, Stokes I. ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion--part I: ankle, hip, and spine. International Society of Biomechanics. J Biomech. 2002;35:543-548.  101  3 Integrated Discussion 3.1 Motivation and findings The goal of this thesis work was to determine how cam FAI alters hip kinematics and to gain insight into the effect of osteochondroplasty on hip kinematics. Active unconstrained flexion and abduction was created in six cadaveric hemi-pelves under several deformity conditions. Motion of the femur was tracked allowing for calculation of flexion, abduction and internal rotation angles as well as translation of the rotational center of the femoral head. A load cell on the cable simulating the active muscle also allowed for measurement of the force required to create motion. Translations, coupled motions and force requirements were compared based on the severity of deformity.  3.1.1 Coupled motions The hypothesis that increased deformity severity would cause increased adduction and increased external rotation during flexion was proved; however, the hypothesis that increased deformity severity would cause increased extension and increased external rotation during abduction was proved for extension but not for external rotation. Coupled motions in the hip are due to two things. First, the direction of force due to the muscle may not be purely in the plane of motion, therefore the femur would be pulled in out-of-plane as well as in-plane motions. Second, interference between the femur and acetabulum or soft tissues creates additional forces acting on the femur, causing the direction of rotation to change. Since the line of action of the muscles is the same independent of deformity condition, any changes to out-of-plane motions due to deformity severity are a result of the second mechanism: interference between the femur and acetabulum. Large ranges of motion in flexion, abduction and internal rotation at 90° 102  flexion causes pain in patients with cam FAI [2, 8, 11]. From these reports, we hypothesized that the pain was occurring due to contact between the deformity and labrum and that during unconstrained flexion and abduction, contact between the femur and acetabulum would occur differently, creating changes to out-of-plane motions. In the current study, this hypothesis was proved during prescribed flexion. During prescribed abduction, however, it was found that while increased extension was observed as predicted, increased internal rotation occurred, contrary to the predictions. On closer observation, we found that during abduction, as the femoral headneck region contacts the acetabulum, the superior portion of a cam deformity interferes in the superior region of the acetabulum (Figure 3-1). Since the deformity is located in the anterosuperior region, the acetabulum is going to apply an anteriorly directed force to the femur, rotating it internally.  The findings of increased internal rotation with increased deformity  severity were, therefore, logical despite internal rotation being labeled as an impinging motion.  103  Figure 3-1: Pelvic anatomy. Black arrow indicates lip on superior region of acetabulum which would apply an anterior force to the cam deformity during abduction, rotating the femur internally. [3]  When studying rotational movements in cam FAI, almost all previous studies have focused on changes to ROM. Clinical studies have shown that passive ROM in flexion is reduced in patients with cam FAI by 9° from 120° to 111° and abduction is reduced by 4° from 43° to 39° [10], while 3D computer simulations have shown flexion to be reduced by 17° from 122° to 105° and abduction to be reduced by 11° from 63° to 52° in hips with cam FAI [7]. The discrepancy between the 3D simulation and the clinical measurements are likely due to the fact that during the computer simulations ROM is limited by only bony contact, whereas during clinical tests, ROM is potentially limited by bony contact, soft tissue contact, pain, or ability to actively create the motion. It is therefore very difficult to compare ranges of motion between in  104  vivo and ex vivo studies. It makes more sense to compare coupled motions, as was done in the present study. Comparing the cadaveric work presented in the present study to in vivo studies or 3D computer simulations would not be possible if ROM were used as the only outcome since the ROM in a cadaver cannot be compared to ROM in vivo or predicted ROM in simulations. As shown in Chapter 2, the coupled motions found in this study are very similar to those found during an in vivo gait study [6] as well as those found in a computer simulation of walking in patients with SCFE [12].  3.1.2 Translations The hypothesis that increased severity of deformity would cause more translation of the rotational center of the femoral head was proved during flexion, but not proved during abduction, as shown in Chapter 2. The reason for this hypothesis was that at some point during the motion, the deformity would make contact with the acetabulum. For motion to continue, the femur would then rotate about this contact point, thereby prying the femoral head out of the acetabulum. This would be reflected as larger translations of the original COR of the femur. During flexion, the “no deformity” group translated approximately 5mm over 70° of flexion, whereas the severe deformity group translated approximately 6.5mm over the range. We found, however, that during abduction, the severe deformity group translated less than the no deformity group (5mm compared to 6.5mm) over 35° of abduction.  As shown in Appendix D, the  repeatability between trials was 0.51mm; therefore we are confident that the differences are not due to random error in our measurements and set-up. The accuracy of determining the translation, mostly due to determination of the COR, was 2.64mm, larger than the difference between groups. However, since the same COR was used for all trials excluding the resection  105  trials, the accuracy in comparing these groups is 0.23mm, substantially smaller than the difference between groups. Only one previous study has to our knowledge looked at translations in the hip joint. This study compared the location of the COR to the location of the geometric center of the femoral head during passive combined flexion and external rotation ex vivo.  They found that the  anatomical center translated approximately 5mm at 100° flexion and 20° external rotation, and that the sphere-fit COR was an average of 2.1mm from the anatomical center; however the translation of the COR is not reported [9]. It is difficult to compare the active motion used in our study to passive motion presented in this study, however, since the exact forces applied to the femur during passive motion cannot be quantified. It is unclear if the person creating the motion in this study pushed the femur into the acetabulum or pulled it out while applying flexion and external rotation. Regardless our finding of translations of the COR of 5mm at 70° flexion and similar translations at 35° abduction are very similar to those translations previously reported.  3.1.3 Force requirements The third hypothesis that increased deformity severity would result in requiring more force on the active cable to produce flexion and abduction was proved. This hypothesis rested on the assumption that once the deformity made contact with the acetabulum additional force would be required to continue the motion either due to increased translations, changes to out-of-plane motions, cartilage compression or a combination of the above. Increased force could occur due to translations of the femoral head since the moment arm of the muscle about the center of rotation changes. If this moment arm were to decrease, the force required to create the same moment on the femur to produce the required motion would increase. During prescribed flexion,  106  we found a maximum difference in translation of 1.5mm over 70° flexion. This corresponds to a change in the COR of 1.3mm. If the moment arm of a muscle was originally 5cm, this change in translation would require an increase in force of 3% of the original dynamic load plus 3% of the static load to produce the same moment and maintain equilibrium. Since the observed increase in force was over 100% of the original dynamic load, this cannot be the only reason for the increased force. Another reason could be the changes to out-of-plane motions. If the femur is rotated out of the original plane of motion due to contact between the femur and acetabulum, the line of action of the muscle changes and the force is no longer aligned with the direction of motion. Since the in-plane component of the force required to maintain equilibrium has not changed, the resultant muscle force required will be larger. A third explanation for the increased force is that as the femur rotates, the aspherical portion of the femoral head is jammed into the more spherical acetabulum, resulting in cartilage compression and possible strain of other soft tissues such as the ligamentum teres and joint capsule. More force would be required create the same amount of motion due to the force required to strain the soft tissues. Further, joint forces will be applied to the femur perpendicular to the surface tangent. In the case of a spherical femoral head, these forces act through the COR of the femur and do not contribute to moments about the COR. When a cam deformity is present, normal forces will not all act through the COR and will contribute moments. During prescribed flexion and abduction, these moments will act against the motion, thereby requiring more force on the simulated muscle to maintain equilibrium.  107  3.1.4 Resection osteochondroplasty The final hypothesis that resection osteochondroplasty would result in changes to hip kinematics from the native condition was proved for all measured quantities except for translations of the COR of the femoral head during prescribed flexion. We expected that the kinematics of the resected condition would behave as a less severe deformity than the native condition since any bone which might be impinging during the native condition was removed during surgery, creating less interference between the femoral head and the acetabulum. While it is possible that some of the change in amount of translation of the COR of the femur is due to errors in repositioning the specimen after surgery, it is more likely that the increase is due to increased joint laxity since the increase was observed in the inferior direction. During surgery, the femoral head was partially distracted, possibly causing stretching of the joint capsule and ligaments which allowed for more subluxation during flexion than the native condition. All other measurements were either found to have no significant difference between the two groups, or followed the same pattern of change as between varying severity of deformities where the resection condition is considered to have less “deformity” than the native condition.  3.2 Significance of findings 3.2.1 Significance of coupled motions The findings of the present study indicate that increased deformity size results in changes to the coupled motions throughout the range of flexion and abduction, not merely the extremes of motion as had previously been suggested. This suggests that interference between the deformity and the pelvis is occurring which alters the path of motion during tasks of daily living. We speculate that this interference may results in changes to the cartilage strain patterns during these  108  motions. Changes to the out-of-plane motions during flexion and abduction will also result in the requirement to use different muscle strategies to create standard motions. For example, when a patient with cam FAI is flexes her hip during the swing phase of gait, additional adduction will occur. The patient may, then, be required to activate her gluteus medius more than a person with normal hip morphology to produce the same motion. This new muscle strategy will also create a change in the loading patterns occurring across the joint.  3.2.2 Significance of translations We found that translation of the average rotational center of the femur increased with increased deformity severity during prescribed flexion and decreased during prescribed abduction. As described above, changes to translations affect the load required to create flexion and abduction. Translations of the COR will likely result in changes to the patterns of cartilage strain since translations occur as a result of prying of the femoral head out of the acetabulum. Therefore, cam deformities are likely going to lead to changes to the locations of peak cartilage strain, possibly loading areas which had not previously been exposed to such loading and may not have the capacity to support the new loads, thereby resulting in cartilage degeneration. It was surprising that no consistent pattern was observed when comparing the direction of translation with increasing severity of deformity even though significant differences were observed between deformity groups. This may indicate that the alpha angle measurement is not capable of quantifying the aspect of the deformity responsible for changing the direction of translation. We also showed that the native hip joint does not behave as a ball and socket joint. Translation of the average COR of the femur occurred for both prescribed flexion and abduction,  109  showing clearly that the motion is not pure rotation in the native hip as well as in the deformed hip. 3D models of hip motion which model only rotations about the geometrical center of the femur are, therefore, incorrect. Instead, models should include translations.  3.2.3 Significance of force requirement This study showed that more force was required by the agonist muscle to create the same amount of flexion or abduction with more severe deformities than was required in the native hip. There will, therefore, be more force acting across the hip joint during motion in a patient with cam FAI than in a person with normal hip morphology. We speculate that this will likely result in higher mean stress on the articular cartilage since it is unlikely that any increase in contact area due to the deformity will be large enough to compensate for the 100% increase in required force observed during flexion.  3.2.4 Mechanism of joint damage This study was the first to quantify the mechanical effect of cam FAI on the hip, providing insight into how cam FAI might lead to hip OA. It has previously been postulated that cam FAI results in jamming of the aspherical portion of the femoral head into the acetabulum during forceful movement [2].  This results in outside-in abrasion of the acetabular cartilage and  possible avulsion of the cartilage from the labrum and subchondral bone. The findings of this thesis work support this theory, indicating that not only during forceful motion, but also during normal everyday motion in a patient with cam FAI, the femoral deformity is abutting against the acetabulum creating changes in loading and motion patterns. The mechanical theory of OA  110  indicates that changes such as these are likely to further increase the likelihood of developing OA [2].  3.2.5 Clinical significance Based on the findings of this study, it is recommended that resection osteochondroplasty be performed in patients with moderate to severe cam FAI in an attempt to slow the progression of OA by limiting the contact between the antero-superior region of the femoral head-neck and the acetabulum. Conservative treatment strategies have focused on limiting contact by avoiding large ranges of motion; however, the findings of the current study show that contact is occurring between the deformity and the acetabulum during ranges of motion consistent with the tasks of everyday life such as walking and climbing stairs, especially in moderate and severe deformities. As such, conservative treatments will be ineffective. Further, changes to coupled motions and translations due to deformity severity represent changes to the contact mechanics occurring within the joint. The changes to these motions are a result of changes to forces applied to the femoral head by the acetabulum. This will likely result in changes in loading patterns of the hip joint which may result in loading of cartilage areas that had previously not been loaded as heavily and therefore are less capable of carrying load, possibly leading to cartilage degeneration. This was further demonstrated by the fact that following resection osteochondroplasty, the femur was more internally rotated and abducted during flexion and more externally rotated and extended during abduction indicating that less contact between the femoral head-neck and acetabulum was occurring during motion.  111  3.3 Study strengths and limitations 3.3.1 Study strengths This thesis work had a number of strengths. Actual cadaver hips were used rather than computer models. Soft tissues were retained in the cadavers, in contrast with the interactions that had previously been modeled. Further, simulation of deformities on each cadaver allowed for the ability to use each specimen as its own control. A large physiological ROM in both flexion and abduction was used.  Most previous cadaveric studies have only studied the  mechanics of the hip joint during simulated one-legged stance and have not studied hip motion. 3D tracking of the motion using a very accurate system allowed for measurements of out-ofplane as well as in-plane motions, in addition to translations, which had not previously been studied. Use of muscle actuation to create motion allows for more physiologic joint mechanics because it has been shown that the pelvis deforms due to muscle loading, creating more contact area between the femur and acetabulum [1].  3.3.2 Study limitations As described in Chapter 2, there were limitations in this thesis work. Three categories of limitations were identified: limitations due to the specimens, limitations due to the simulated deformities and limitations due to the simulated motion. The first category of limitations is limitations due to the nature of the specimens used. The specimens used were cadaveric and, therefore, it is difficult to generalize the results to in vivo conditions. The current study could not have been performed in vivo since precise measurements of muscle force are not currently possible in vivo and motion tracking in vivo is not accurate enough to study small translations due to soft tissue artifact. Further, the specimens were an  112  average of 79.2 years of age at the time of death. As a result, OA and femoral head deformities were present in two of the six specimens.  Finally, the specimens were hemi-pelves with  proximal femurs. This meant that traditional methods of identifying the joint coordinate systems [13] could not be used since the pelvic coordinate system requires the presence of both ASIS’s and both PSIS and the femoral coordinate system requires the presence of the femoral epicondyles. As a result, a different method of calculating the pelvic coordinate system was used, and the femoral coordinate system was assumed to be aligned with the pelvic coordinate system when the femur was in neutral position. This method may have been less accurate than the standard method outlined by Wu et al. (2002) [13]. As a result, there is a possibility that some of the observed motion coupling is due to axial misalignment rather than actual coupling, as described in Chapter 2. This artifact, however, is only present when comparing results to the standard reference frame. Differences observed between deformity groups in the present study must be due to deformity severity since the same coordinate system was used for all specimens and all deformity conditions within each specimen. The presence of only the proximal half of the femur, rather than the entire lower limb also meant that bi-articular muscles could not be used to load the joint. The second category of limitations relates to the simulated deformities. These deformities may not have had the exact geometry or properties of a native deformity. Care was, however, taken to ensure that the geometry of the deformities was as close to physiologic as possible. This was done by studying MR, CT and photographic images of femurs with cam lesions, then attempting to replicate the geometry observed. The most difficult part to ensuring physiologic likeness was the transition between the native bone and the simulated deformity. Since the deformity was required to be removable, it could not be rigidly attached in all locations.  113  Therefore, a small gap may have been present at the transition between the native bone and deformity. During motion, it is possible that a small gap may result in snagging with the soft tissues or acetabulum. Therefore, care was taken to create as smooth a transition as possible to prevent such an occurrence. A second limitation due to the simulated deformities was that they required the joint capsule to be opened to create them. An open joint capsule may result in a less stable joint and possibly allow more translations than a closed joint capsule. Also, the open joint capsule meant that little or no synovial fluid was present during testing. This may have resulted in more contact between the femur and the acetabulum than in an in vivo situation. The joint capsule was, however, opened as little as possible while allowing access to the joint and easy transition between deformity conditions. Also, the capsule was open during testing under all deformity conditions and, therefore, any changes seen between groups are due to the simulated deformity and not the open joint capsule. Thirdly, limitations exist due to the nature of the measurements of deformity size. The alpha angle is the standard measurement used clinically for determining the size of deformity. This measurement, however, does not take into account the 3D nature of the deformity geometry and, therefore, there may be aspects of the deformities which are affecting the 3D motions and forces observed which were not quantified. Other measurements, such as the triangular index and anterior offset ratio, could have been used to quantify the deformity; however, these methods are not as widely used as the alpha angle. Alpha angle, triangular index and offset ratio measurements for all six specimens and five deformity conditions are provided in Appendix F. The third category of limitations is limitations due to the simulated motion. The muscle force data required to create motion at the hip joint using simulated muscles are not currently available. Some electromyography (EMG) data are available which provide information about  114  which muscles are active during certain motions, however, these data are only available for superficial muscles which are not necessarily the most important muscles at the hip joint. In this study, physiological cross-sectional areas were used to help choose which muscles to simulate (Appendix B). These data provide information about the relative size of each muscle, which allows for inference about which is capable of providing the most force and is, therefore, the most likely to be creating motion.  As such, the forces used may not have been entirely  physiologic. A force of 11N was placed on each “static” muscle (muscles not shortened to create motion). This was the force required to keep the femoral head firmly within the acetabulum while still allowing easy manipulation of the femur. In vivo, it is likely that these muscle loads would be changing throughout the motion as the length of the moment arm changes, however these data are not available. The load and loading rate applied to the active muscle for each motion was chosen based on trial and error. This load was conservative and did not allow for a full ROM. This was done to prevent damage to the specimen. Finally, the loading condition created was non-weightbearing. This type of loading was chosen to simulate more closely actions which are causing pain in FAI patients such as the swing phase of gait and large motions such as flexion and abduction which are not normally done during weightbearing. This also allowed better comparison with previously published data on the affect of FAI on gait and ranges of motion.  3.4 Future directions The findings in the present study demonstrate that the hip joint is not a pure ball and socket joint where all motions are pure rotations. Instead, it suggests that the “center of rotation” is experiencing small translations of approximately 5mm, in other words, there is a changing COR  115  throughout the motion rather than a fixed one. In the present study, an open joint capsule was required and, therefore, it is possible that more translation occurred than would have in a closed joint capsule. A study, therefore, needs to be performed which quantifies the extent to which the hip joint can be modeled as a ball and socket joint in cadaveric hip joints with closed joint capsules. This study should quantify the ROM over which the hip joint can be modeled as a pure rotation as well as what happens outside of this ROM. This could be performed ex vivo, allowing for very accurate motion tracking. It may also be desirable to perform a similar study in vivo using open MRI which would allow visualization of any hip distraction. It may also be possible to determine the location of the functional COR compared to the geometrical center of the femoral head. Once the normal kinematics of the hip have been confirmed using the above study, it would be useful to determine whether the results of that study as well as the current study can be applied in vivo. This will involve repeating the motions described above as well as the motions of the current study in live people and tracking the motion, to confirm that the same motion is occurring in vivo as we have found ex vivo. The biggest problem with this, however, is tracking the motions of the femur and pelvis accurately enough to be able to detect the small translations observed. Retroreflective markers will not work since the soft tissue artifact due to placing the markers on skin or clothing is greater than the observed translations. Instead, a new method of tracking motion must be developed. A potential method would be to use an open MRI system which allows for the subject to produce large motions while imaging without radiation. A problem with this is that due to the nature of a MR scan sequence, the subject would need to produce repeatable motions. A MR safe rig would need to be designed which could guide the subject’s motion, allowing for high repeatability.  116  Once the normal hip kinematics have been established, the results of this study combined with results of the above study can be used to help create an accurate 3D model of hip motion in deformed joints. The statistical models provided in Chapter 2 provide information that would be useful in determining the motion paths that will occur in the deformed hip. These 3D models could then be used to assist in surgical planning by allowing the surgeon to experiment with resection locations to determine the best correction which will restore normal kinematics and, therefore, most likely restore normal joint mechanics. Assessing the effect of cam FAI on additional motions may also be a future direction of this research.  These motions could include active unconstrained internal rotation or combined  motions involving actively shortening more than one muscle at a time. This would allow for further understanding of the motion at the hip and how it is affected by cam FAI and would provide additional data required for creating 3D models of hip motion. It may also be desired to create weightbearing motions ex vivo such as representing walking, sit-to-stand and squatting. Another important future direction would be to study the relationship between translations within the hip and cartilage strain. As proposed in this thesis, translation of the “center of rotation” means that the COR is moving throughout the motion. In a joint such as the hip where the femoral head and acetabulum are almost spherical, this means that the rotation is no longer occurring about the center of the femoral head and, therefore, areas of high cartilage strain should be occurring. This is, however, speculative and has not been proven. A study which examines the relationship between the location of the COR and the amount of cartilage strain would be very helpful in proving this theory, though is likely not possible at this time due to complications in measuring both the COR and cartilage strain accurately enough.  117  Further, cartilage strain could also be studied in specimens with varying severity of cam deformity. Deformities could be simulated using the methods presented in the current study and changes to cartilage strain could be measured using methods similar to those of Greaves et al. (2010) using 7T MRI [4]. This would provide further understanding of the mechanism by which cam FAI produces hip OA. It may also allow better understanding of how best to correct the deformity to prevent increased cartilage strain. Finally, a study to answer the question “Is resection osteochondroplasty slowing or preventing the development of hip OA” needs to be performed. This would require a large dataset of patients including one group of patients with cam FAI who undergo resection osteochondroplasty and a second age, gender and BMI matched group of patients with cam FAI who do not undergo resection osteochondroplasty. Long-term follow-up would be required to determine if the likelihood of developing hip OA is changed by the resection osteochondroplasty.  3.5 Conclusions This thesis work was the first to create active unconstrained motion in the cadaveric hip joint, to study translations in combination with coupled motions and to look at the effect of cam lesions on translations of the COR of the hip, coupled motions and force requirements in cadaveric hips. The findings indicate that cam lesions affect more than just ROM of the hip. Out-of-plane motions, translations of the center of rotation and the force required to create both flexion and abduction are altered throughout the entire range of motion, indicating that the deformity is affecting hip biomechanics not merely at the extremes of motion, but also during motions within the range typical of everyday living. These changes are likely due to interactions between the deformity and soft tissues such as the labrum and joint capsule. As such, it is recommended that  118  models of hip motion in cam FAI include soft tissues and that resection osteochondroplasty be considered rather than conservative treatments which advise only to avoid extreme motions. Further, the findings of this study indicate that a pure ball and socket model of the hip joint is not always appropriate since translations are occurring not only in the deformed hip but also in the normal hip.  119  3.6 References  1. Bay B, Hamel A, Olson S, Sharkey N. Statically equivalent load and support conditions produce different hip joint contact pressures and periacetabular strains. J Biomech. 1997;30:193196. 2. Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock K. FAI: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003:112-120. 3.  Gray H. Anatomy of the Human Body. Philidelphia: Lea & Febiger; 1918.  4. Greaves L, Gilbart M, Yung A, Kozlowski P, Wilson D. Effect of acetabular labral tears, repair and resection on hip cartilage strain: A 7T MR study. J Biomech. 2010;43:858-863. 5. Kedgley A, Mackenzie G, Ferreira L, Drosdowech D, King G, Faber K, Johnson J. The effect of muscle loading on the kinematics of in vitro glenohumeral abduction. J Biomech. 2007;40:2953-2960. 6. Kennedy M, Lamontagne M, Beaulé P. FAI alters hip and pelvic biomechanics during gait Walking biomechanics of FAI. Gait Posture. 2009;30:41-44. 7. Kubiak-Langer M, Tannast M, Murphy S, Siebenrock K, Langlotz F. Range of motion in anterior FAI. Clin Orthop Relat Res. 2007;458:117-124. 8.  Laude F, Boyer T, Nogier A. Anterior FAI. Joint Bone Spine. 2007;74:127-132.  9. Lopomo N, Sun L, Zaffagnini S, Giordano G, Safran M. Evaluation of formal methods in hip joint center assessment: an in vitro analysis. Clin Biomech (Bristol, Avon). 2010;25:206-212. 10. Philippon M, Maxwell R, Johnston T, Schenker M, Briggs K. Clinical presentation of FAI. Knee Surg Sports Traumatol Arthrosc. 2007;15:1041-1047. 11.  Pulido L, Parvizi J. FAI. Semin Musculoskelet Radiol. 2007;11:66-72.  12. Rab G. The geometry of slipped capital femoral epiphysis: implications for movement, impingement, and corrective osteotomy. J Pediatr Orthop. 1999;19:419-424. 13. Wu G, Siegler S, Allard P, Kirtley C, Leardini A, Rosenbaum D, Whittle M, D'Lima D, Cristofolini L, Witte H, Schmid O, Stokes I. ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion--part I: ankle, hip, and spine. International Society of Biomechanics. J Biomech. 2002;35:543-548.  120  Appendix A: Ethics  121  122  123  Appendix B: Muscles that Cross the Hip Joint  124  B.1 Tables of muscles Muscle Adductor magnus  Biceps femoris  Proximal attachment Adductor part: Pubis and ischium  Distal attachment Adductor part: Linea aspera  Joints crossed Hip  Hamstring part: Ischial tuberosity  Hamstring part: Adductor tubercle  Long head: Ischial tuberosity  Head of fibula  Hip Knee  Short head: Linea aspera  Gracilis  Pubis  Tibia  Iliacus  Lesser trochanter  Pectineus  Iliac crest and fossa Pubis  Hip Knee Hip  Lesser trochanter  Hip  Psoas major  T12-L5  Lesser trochanter  Rectus femoris  AIIS  Patella  Sartorius  ASIS Iliac spine  Tibia  Hip Lumbar vertebrae Hip Knee Hip Knee  Semimembranosus  Ischial tuberosity  Medial condyle  Semi-tendinosus  Tensor of fascia latae  Ischial tuberosity  ASIS  Tibia  Lateral condyle  Hip  Hip Knee  Hip Knee  Table B-1: Flexor muscles.  125  Function at hip joint Adductor part: Flexion Adduction Hamstring part: Adduction Extension When knee flexed: Flexion Lateral rotation When extended: Extension Flexion Adduction Flexion  PCSA [1] 48.6  39.0  knee  4.9 27.2  Flexion Adduction Flexion  6.8  Flexion  28.9  Flexion Abduction Lateral rotation When knee flexed: Flexion Medial rotation  11.8  When knee extended: Extension When knee flexed: Flexion Medial rotation When knee extended: Extension Abduction Medial rotation Flexion  19.5  17.1  14.7  8.8  Muscle Adductor magnus  Biceps femoris  Proximal attachment Adductor part: Pubis and ischium  Distal attachment Adductor part: Linea aspera  Joints crossed Hip  Hamstring part: Ischial tuberosity  Hamstring part: Adductor tubercle  Long head: Ischial tuberosity  Head of fibula  Hip Knee  Short head: Linea aspera  Gluteus maximus  Semimembranosus  Semi-tendinosus  Ilium, dorsal surface of sacrum and coccyx Ischial tuberosity  Ischial tuberosity  Gluteal tuberosity, lateral condyle  Hip Sacroiliac Knee  Medial condyle  Hip  Tibia  Hip Knee  Function at hip joint Adductor part: Flexion Adduction Hamstring part: Adduction Extension When knee flexed: Flexion Lateral rotation When extended: Extension Extension  Table B-2: Extensor muscles.  126  48.6  39.0  knee  72.2  When knee flexed: Flexion Medial rotation When knee extended: Extension When knee flexed: Flexion Medial rotation When extended: Extension  PCSA [1]  knee  17.1  14.7  Muscle  Distal attachment Greater trochanter  Joints crossed Hip  Gluteus minimus  Proximal attachment Superior surface of ilium Surface of ilium  Greater trochanter  Hip  Obturator internus Piriformis  Obturator foramen Sacrum  Greater trochanter  Hip  Greater trochanter  Hip Sacroiliac  Gluteus medius  Sartorius  ASIS Iliac spine  Tibia  Hip Knee  Tensor of fascia latae  ASIS  Lateral condyle  Hip Knee  Proximal attachment Pubis Pubis Adductor part: Pubis and ischium  Distal attachment Linea aspera Linea aspera Adductor part: Linea aspera  Joints crossed Hip Hip Hip  Hamstring part: Ischial tuberosity  Hamstring part: Adductor tubercle  Ischial tuberosity  Greater trochanter  Function at hip joint Abduction Medial rotation Abduction Medial rotation Lateral rotation Abduction When hip flexed: Abduction When hip extended: Lateral rotation Flexion Abduction Lateral rotation Abduction Medial rotation Flexion  PCSA [1]  98.7 25.5 25.4 8.1  11.8 8.8  Table B-3: Abductor muscles.  Muscle Adductor brevis Adductor longus Adductor magnus  Gemellus inferior  Gemellus superior  Ischial tuberosity  Greater trochanter  Gracilis  Pubis  Tibia  Pectineus  Pubis  Lesser trochanter  Hip  Hip  Hip Knee Hip  Table B-4: Adductor muscles.  127  Function at hip joint Adduction Adduction Adductor part: Flexion Adduction Hamstring part: Adduction Extension When hip flexed: Adduction When hip extended: Lateral rotation When hip flexed: Adduction When hip extended: Lateral rotation Flexion Adduction Flexion Adduction  PCSA [1] 10.5 15.1 48.6  4.1  4.1  4.9 6.8  Muscle Biceps femoris  Proximal attachment Long head: Ischial tuberosity  Distal attachment Head of fibula  Joints crossed Hip Knee  Short head: Linea aspera  Gemellus inferior  Gemellus superior  Obturator externus Obturator internus Piriformis  Quadratus femoris Sartorius  Ischial tuberosity  Ischial tuberosity  Obturator foramen Obturator foramen Sacrum  Ischial tuberosity ASIS Iliac spine  Greater trochanter  Greater trochanter  Hip  Hip  Function at hip joint When knee flexed: Flexion Lateral rotation When knee extended: Extension When hip flexed: Adduction When hip extended: Lateral rotation When hip flexed: Adduction When hip extended: Lateral rotation Lateral rotation  Trochanteric fossa  Hip  Greater trochanter  Hip  Greater trochanter  Hip Sacroiliac  Lateral rotation Abduction When hip flexed: Abduction  Hip  When hip extended: Lateral rotation Lateral rotation  Inter-trochanteric crest Tibia  Hip Knee  Table B-5: Lateral rotator muscles.  128  Flexion Abduction Lateral rotation  PCSA [1] 39.0  4.1  4.1  30.1 25.4 8.1  14.6 11.8  Muscle Gluteus medius Gluteus minimus Semimembranosus  Semi-tendinosus  Tensor of fascia latae  Proximal attachment Superior surface of ilium Surface of ilium  Distal attachment Greater trochanter  Joints crossed Hip  Greater trochanter  Hip  Ischial tuberosity  Medial condyle  Hip  Ischial tuberosity  ASIS  Tibia  Lateral condyle  Hip Knee  Hip Knee  Function at hip joint Abduction Medial rotation Abduction Medial rotation When knee flexed: Flexion Medial rotation When knee extended: Extension When knee flexed: Flexion Medial rotation When knee extended: Extension Abduction Medial rotation Flexion  PCSA [1] 98.7 25.5 17.1  14.7  8.8  Table B-6: Medial rotator muscles.  B.2 References 1. Klein Horsman M, Koopman H, van der Helm F, Prosé L, Veeger H. Morphological muscle and joint parameters for musculoskeletal modelling of the lower extremity. Clin Biomech (Bristol, Avon). 2007 Feb;22(2):239-47.  129  Appendix C: Dynamic Hip Motion Simulator  130  C.1 DHMS frame The frame of the DHMS was designed and built by Filzer™. It was designed to be extremely adjustable while being rigid and sterilizable. As such, aluminum channels were chosen for the frame. The final design is shown in Figure C-1.  Figure C-1: Dynamic Hip Motion Simulator (DHMS). A) Locking wheels. B) Horizontal sliding pulley bars which lock into place. C) Vertical sliding specimen attachment bar. D) Rotating specimen attachment plate. E) Angle adjustment for specimen attachment bar. F) Vertical posts for pulleys, adjustable in height and angle and along the pulley bars (B). G) Pulleys.  131  C.2 Motion Motion was created in the specimens by shortening one simulated muscle while statically loading the others (Figure C-2). Muscles were shortened using a servo motor (2115-0-00-00-000-T-E-C-x-0, Cleveland Motion Controls, Billerica, MA) with a 10:1 gearbox (23SP010, Carson Manufacturing, Servo Systems Co., Montville, NJ).  Motors were controlled by a custom  Labview™ program which increased the supplied voltage by 0.03V/s until a maximum force of 156N was detected by the in-line load cell (HIS-S-250, S-type 250lb load cell, Hoskins Scientific, Vancouver BC). The driving voltage was outputted via a data acquisition system (DAQ) (National Instruments, Austin, TX) to a current amplifier (16A20AC, Advanced Motion Controls, Camarillo, CA) which outputted to the motors.  132  Figure C-2: Schematic of the motion control system. Custom Labview™ code controlled the DAQ output which went through a current amplifier to the motors which shortened the cables, creating motion. Feedback was provided through load cells in line with the cables.  133  Appendix D: Quantification of Sources of Error  134  D.1 Marker tracking error The error due to marker tracking was almost negligible. The Optotrak Certus (Northern Digital Instruments, Waterloo, ON) tracks optoelectronically with 0.1mm accuracy.  D.2 Marker motion error Distances between markers were calculated throughout all 24 trials (resection condition not included since markers were removed for the surgery). The minimum distance subtracted from maximum distance was determined for each pair of markers on the femur and each pair of markers on the pelvis. The maximum value was found for each specimen and is summarized in Table D-1. Specimen Maximum change in distance between any two markers 4.0827mm 1 2.1922mm 2 3.3714mm 3 2.5459mm 4 1.9394mm 5 2.6517mm 6 Table D-1: Summary of maximum change in distance between any two markers.  Due to the slightly “unrigged” nature of the markers (as described above by relative change in distance between markers), small errors in calculating the transformation matrix occurred. This was calculated by first finding the point error (transformation matrix*initial position – final position). The total error was then found by summing the norm of the point errors for all markers. The transformation error was the total error divided by the number of markers. The maximum transformation error for each specimen is given in Table D-2.  135  The average  transformation error over all trials and all specimens was 0.0999mm. transformation error over all trials and all specimens was 1.1050mm.  The maximum  The 95th percentile  transformation error was 0.2261mm. The maximum transformation error was much smaller than the maximum change in distance between markers due to the optimization routine used to determine the transformation matrix. The 95th percentile transformation error (0.2261mm) was taken to be the error due to marker motion.  Specimen  Maximum transformation error 1.0048mm 1 0.8069mm 2 1.1050mm 3 0.4585mm 4 0.8677mm 5 0.6896mm 6 Table D-2: Summary of the maximum transformation error.  D.3 System origin error For each specimen, the origin for the native and three simulated deformity conditions was determined by taking the average COR for the three native flexion trials and the three native abduction trials. The origin for the resected condition was determined by taking the average COR for the three resected flexion trials and the three resected abduction trials. The error in determining the system origin was determined by finding the difference between each of these six trials. It was determined that the average distance between COR trials was 1.95mm, with a standard deviation of 2.06mm. The 95th percentile value was 2.43mm. This was determined to be the error in determining the system origin.  136  D.4 System axes error For two specimens, the points on the pelvis were digitized before and after testing. For these specimens, the rotation matrix to create the pelvic coordinate system was determined using both the pre-testing points and the post-testing points and the angle between these matrices was determined. The results are summarized in Table D-3. The 95% value for all rotations was 4.6°. This value was taken to be the error in the system axes.  Specimen Pre or Post resection  Angle  Flexion Abduction Internal Rotation Post Flexion Abduction Internal Rotation Pre Flexion 4 Abduction Internal Rotation Post Flexion Abduction Internal Rotation Table D-3: Summary of repeatability in determining system axes. 3  Pre  Difference between matrices 6.2° 7.0° 0.2° 2.1° 2.4° 0.4° 3.1° 2.0° 0.6° 5.6° 3.6° 4.4°  D.5 Total translation error How the origin error affected translations was determined by creating an ideal data set with markers located at similar locations as the specimens and rotating these markers about their perfect origin to angles of 70° flexion and 40° abduction. The location of the origin was then moved in all three directions and the process was repeated. Rotations and translations were  137  calculated. Rotations were unaffected by origin location, but changes in translational values are given below in Equations D-1 through D-6.  During flexion (T = translation error, O = offset in origin location): Equation D-1  T_x = 0.134*O_z  Equation D-2  T_y = 0.992*O_x + 0.236*O_z  Equation D-3  T_z = 0.174*O_y  During abduction: Equation D-4  T_x = 0.058*O_z  Equation D-5  T_y = 0.058*O_x + 0.716*O_z  Equation D-6  T_z = 0  As can be seen from these equations, in both cases, the translation error is largest in the ydirection (superior/inferior) and is most dependent on errors in origin in the X-direction (anterior/posterior) for flexion and Z-direction (medial/lateral) for abduction. The worst case scenario would be for the entire origin error to be in the x-direction, resulting in a translational error or 0.992*origin error for all flexion trials. As such, the origin error of 2.43mm corresponds to a translation error of 2.41mm. The total translational error was taken to be the translational error due to origin error (2.41mm) plus the translational error due to marker motion (0.23mm). The total translational error was 2.64mm.  138  D.6 Total angle error The total error in the angle measurements was the sum of the error due to determining the system axes (4.6°) and the angle error due to translational error (asin(translational error/minimum distance from origin to marker)). The minimum distance from the origin to a marker for any trial was 104.12mm. As such the angle error due to translational error was determined to be 1.4°. The total angle error was 6.0°.  D.7 Deformity quantification error Measurement of the alpha angle was performed by first determining the best fit circle of the femoral head for each slice by choosing 10 points around it. The center of the femoral neck was determined by selecting 10 points on one each side of the femoral neck then finding the minimum distance between them. A line was drawn from the center of the femoral neck to the center of the femoral head. A point was then chosen where the femoral head first exceeded the best fit circle. The angle between the line from the exceeding point to the center of the femoral head and the previous line was determined. This entire process was repeated for each specimen, deformity condition and slice three times. An average standard deviation of 3.5° was found (sd 4.2°).  D.8 Repeatability of motion Each motion was repeated three times with each deformity condition on each specimen. As such, repeatability could be assessed. It was found that during flexion, there was an average between trial standard deviation of 2.11° of abduction (sd 1.87°), 1.39° of internal rotation (sd  139  1.21°), 0.51mm of translation (sd 0.74mm°) and 9.16N of force (sd 7.16N). During abduction, there was an average between trial standard deviation of 1.17° flexion (sd 0.93°), 1.45° internal rotation (sd 1.20°), 0.97mm translation (sd 1.52mm) and 10.72N force (sd 10.94N).  140  Appendix E: Additional Results  141  Figure E-1: Internal rotation angles during prescribed flexion for each individual specimen.  142  Figure E-2: Abduction angles during prescribed flexion for each individual specimen.  143  Figure E-3: Euclidean translation of the COR of the femur during prescribed flexion for each individual specimen.  144  Figure E-4: Translation of the COR of the femur along the X-axis during prescribed flexion. Positive translation along the X-axis corresponds to translation in the anterior direction.  145  Figure E-5: Translation of the COR of the femur along the Y-axis during prescribed flexion. Positive translation along the Y-axis corresponds to translation in the proximal direction.  146  Figure E-6: Translation of the COR of the femur along the Z-axis during prescribed flexion. Positive translation along the Z-axis corresponds to translation in the lateral direction.  147  Figure E-7: Force required to create prescribed flexion for each individual specimen.  148  Figure E-8: Internal rotation angles during prescribed abduction for each individual specimen.  149  Figure E-9: Flexion angles during prescribed abduction for each individual specimen.  150  Figure E-10: Euclidean translation of the COR of the femur during prescribed abduction for each individual specimen.  151  Figure E-11: Translation of the COR of the femur along the X-axis during prescribed abduction. Positive translation along the X-axis corresponds to translation in the anterior direction.  152  Figure E-12: Translation of the COR of the femur along the Y-axis during prescribed abduction. Positive translation along the Y-axis corresponds to translation in the proximal direction.  153  Figure E-13: Translation of the COR of the femur along the Z-axis during prescribed abduction. Positive translation along the Z-axis corresponds to translation in the lateral direction.  154  Figure E-14: Force required to create prescribed abduction for each individual specimen.  155  Figure E-15: Internal rotation angles during prescribed flexion for each individual specimen, comparison of native and resected conditions.  156  Figure E-16: Abduction angles during prescribed flexion for each individual specimen, comparison of native and resected conditions.  157  Figure E-17: Euclidean translation of the COR of the femur during prescribed flexion for each individual specimen, comparison of native and resected conditions.  158  Figure E-18: Translation of the COR of the femur along the X-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the X-axis corresponds to translation in the anterior direction.  159  Figure E-19: Translation of the COR of the femur along the Y-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the Y-axis corresponds to translation in the proximal direction.  160  Figure E-20: Translation of the COR of the femur along the Z-axis during prescribed flexion, comparison of native and resected conditions. Positive translation along the Z-axis corresponds to translation in the lateral direction.  161  Figure E-21: Force required to create prescribed flexion for each individual specimen, comparison of native and resected conditions.  162  Figure E-22: Internal rotation during prescribed abduction for each individual specimen, comparison of native and resected conditions.  163  Figure E-23: Flexion angles during prescribed abduction for each individual specimen, comparison of native and resected conditions.  164  Figure E-24: Euclidean translation of the COR of the femur during prescribed abduction for each individual specimen, comparison of native and resected conditions.  165  Figure E-25: Translation of the COR of the femur along the X-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the X-axis corresponds to translation in the anterior direction.  166  Figure E-26: Translation of the COR of the femur along the Y-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the Y-axis corresponds to translation in the proximal direction.  167  Figure E-27: Translation of the COR of the femur along the Z-axis during prescribed abduction, comparison of native and resected conditions. Positive translation along the Z-axis corresponds to translation in the lateral direction.  168  Figure E-28: Force required to create prescribed abduction for each individual specimen, comparison of native and resected conditions.  169  Appendix F: Deformity Measurements  170  Specimen 1  2  3  4  5  6  Deformity Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected  0° 63.2 81.4 70.0 57.4 35.5 40.4 38.9 52.2 55.6 51.2 41.9 44.5 45.4 43.5 45.4 79.0 69.4 75.4 65.7 44.6 67.7 61.8 54.0 62.1 47.8 37.2 80.0 68.2 87.3 40.4  5° 47.4 65.0 71.1 72.9 38.8 45.9 42.9 53.6 63.7 53.0 46.9 42.7 45.5 48.3 46.4 47.0 71.3 73.7 77.4 43.3 66.2 59.9 60.3 53.4 42.3 40.2 86.0 76.0 90.3 38.3  10° 75.1 85.0 70.7 80.4 42.0 44.6 44.8 51.6 52.4 50.8 45.6 41.7 43.8 68.1 46.5 56.0 70.3 69.0 70.4 44.3 67.5 45.0 62.9 62.9 43.5 36.8 82.2 77.5 93.5 39.9  15° 47.8 91.3 69.8 57.7 41.6 46.4 45.0 56.0 53.4 45.0 47.4 44.1 43.6 68.2 48.4 64.8 71.5 73.2 74.6 40.8 59.3 58.9 72.0 70.0 43.6 42.1 87.3 83.4 87.7 40.4  20° 46.6 88.3 83.6 68.0 45.5 50.8 55.2 74.0 63.1 44.1 44.6 61.6 54.4 82.3 45.5 71.4 75.0 72.8 75.4 44.1 55.4 66.6 71.6 82.5 39.5 42.4 84.7 84.1 89.4 40.9  25° 54.3 89.7 88.9 44.8 43.3 55.2 63.8 72.2 68.2 44.7 48.3 74.6 68.0 84.9 45.0 64.8 70.8 71.0 75.1 44.7 52.7 76.4 72.4 81.5 40.5 41.4 79.2 86.1 89.1 41.0  30° 45.7 88.6 90.3 86.5 46.2 52.8 66.4 75.9 72.8 41.3 45.8 78.5 79.5 87.3 46.3 71.6 74.7 73.2 78.0 44.2 57.8 78.9 76.9 81.2 40.6 39.0 78.1 82.7 88.1 39.9  35° 53.3 86.3 89.6 93.6 45.1 63.3 73.0 79.1 75.8 40.7 49.0 78.2 92.8 88.3 44.7 70.7 77.3 74.4 78.7 43.5 49.1 79.8 75.7 84.4 39.0 38.4 79.2 84.7 87.2 39.9  40° 41.8 84.4 87.9 91.6 47.4 65.9 73.7 80.0 77.4 38.9 53.3 71.5 96.1 89.4 43.0 67.6 76.8 78.8 77.7 42.1 47.8 80.1 75.9 84.2 40.3 38.5 78.2 82.3 84.2 41.5  Radial slice 45° 50° 55.9 70.0 78.8 79.8 86.5 82.2 88.8 86.0 45.7 54.8 68.5 65.0 74.8 74.9 84.0 82.7 78.4 78.0 40.6 39.3 57.1 53.9 74.8 72.6 94.4 91.3 91.1 93.7 40.5 44.6 72.1 71.1 77.2 78.8 77.7 80.0 77.9 76.3 38.0 36.9 46.9 41.9 79.6 81.4 79.0 81.0 83.5 85.0 38.7 39.6 37.8 40.2 79.6 82.0 82.3 84.5 86.3 85.2 39.1 39.5  Max 55° 69.7 81.2 84.6 79.9 44.9 67.7 74.6 81.8 78.9 37.5 52.6 72.0 92.7 90.1 45.0 70.9 76.5 80.5 78.3 40.0 40.9 82.1 79.0 85.8 40.3 39.3 77.9 83.3 83.3 39.6  60° 55.1 77.6 83.6 82.7 45.9 61.3 75.2 82.0 78.1 37.6 47.2 75.1 93.6 89.2 39.8 71.0 78.2 78.4 77.9 37.1 41.1 83.9 79.4 87.2 40.2 34.1 73.7 81.3 82.7 39.1  65° 62.9 77.6 81.3 80.0 45.5 67.0 75.5 80.6 77.4 39.7 45.2 77.8 96.4 91.7 39.2 69.8 80.0 78.8 77.7 38.9 44.8 83.6 82.9 85.6 37.9 30.5 72.3 81.5 72.3 37.1  70° 54.2 77.0 83.5 83.8 46.8 65.4 71.7 79.2 75.7 39.4 46.3 77.9 93.9 87.0 38.8 71.7 78.1 79.1 75.7 40.9 43.3 84.3 77.1 87.2 39.3 34.9 69.4 76.4 39.9 40.9  75° 64.5 76.1 83.1 78.4 43.9 58.5 73.0 78.7 72.5 38.6 43.3 72.2 93.6 88.9 37.2 63.2 78.1 76.2 74.7 39.4 41.5 85.0 78.8 83.9 40.0 39.9 65.1 67.5 34.0 40.5  80° 46.9 77.2 81.6 79.2 41.5 55.8 70.7 77.2 68.2 38.2 45.1 77.2 91.5 88.0 37.2 60.0 76.2 76.8 71.5 38.2 40.6 84.5 74.8 83.3 40.0 47.4 59.9 45.6 48.4 42.5  85° 52.1 69.6 79.2 74.6 40.1 48.1 66.0 74.8 63.4 41.1 44.6 83.8 85.1 88.1 36.8 61.5 67.6 76.3 67.8 39.8 43.4 77.2 70.9 80.9 41.4 49.5 57.8 53.2 40.0 39.4  90° 46.7 59.6 57.5 71.5 40.3 47.7 53.5 75.2 78.5 41.0 47.2 72.6 84.1 88.0 35.8 61.7 59.1 77.6 56.5 39.8 42.7 68.9 60.3 74.7 41.5 46.8 49.5 47.1 42.7 43.3  75.1 91.3 90.3 93.6 54.8 68.5 75.5 84.0 78.9 53.0 57.1 83.8 96.4 93.7 48.4 79.0 80.0 80.5 78.7 44.7 67.7 85.0 82.9 87.2 47.8 49.5 87.3 86.1 93.5 43.3  Table F-1: Summary of alpha angle measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given.  171  Specimen 1  2  3  4  5  6  Deformity Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected  0° -6.6 0.6 -1.9 -7.6 -9.4 -5.1 -7.5 -5.1 -2.4 -4.3 -4.9 -2.7 -3.6 -3.6 -6.8 -0.2 -1.1 -0.5 -1.7 -8.3 -1.8 -2.3 -2.4 -2.4 -3.3 -6.3 1.1 2.1 4.2 -7.5  5° -7.6 -1.2 -2.6 -6.1 -8.1 -3.4 -6.3 -3.6 -1.5 -3.2 -3.3 -5.1 -3.1 -3.4 -7.1 -4.0 -0.8 -0.9 -0.2 -7.3 -1.1 -2.7 -2.9 -3.3 -6.9 -3.5 0.9 3.3 4.9 -8.1  10° -3.1 -1.7 -5.1 -1.8 -8.4 -3.6 -6.8 -3.2 -2.1 -5.9 -3.9 -4.5 -4.2 -1.3 -6.7 -1.6 -0.9 -1.9 -0.9 -8.1 -2.0 -3.3 -1.9 -1.5 -7.4 -2.1 1.5 3.1 4.8 -7.2  15° -7.1 1.5 -1.1 -4.4 -7.0 -3.5 -3.1 -3.6 -3.6 -8.4 -3.7 -4.0 -4.3 1.4 -6.9 -0.9 -1.1 -0.8 -0.2 -8.9 -2.2 -2.6 1.8 0.4 -6.6 -3.2 1.4 3.4 4.3 -6.5  20° -6.8 2.6 3.0 -1.2 -6.1 -3.2 -3.2 1.9 -2.6 -9.4 -3.3 -2.2 -3.3 1.8 -7.3 -0.9 0.5 -1.5 3.7 -8.4 -3.0 1.9 2.6 5.0 -7.2 -2.2 1.3 3.2 4.7 -5.8  25° -4.3 2.5 2.4 -8.3 -7.5 -2.2 -2.7 2.2 0.4 -9.0 -2.7 -1.3 0.9 3.3 -6.6 -0.8 3.3 2.6 4.4 -8.1 -2.3 2.4 3.0 6.4 -8.8 -2.1 1.0 3.4 5.4 -5.9  30° -6.9 3.2 4.9 5.4 -4.0 -3.7 0.6 4.4 1.8 -7.4 -3.2 -0.7 1.4 3.9 -7.0 0.1 4.2 2.7 5.8 -8.2 -1.7 3.1 4.2 5.3 -7.4 -2.7 2.5 3.5 4.8 -6.9  35° -2.7 3.5 4.4 5.7 -6.4 -3.5 -0.9 3.4 2.4 -8.4 -2.9 -0.5 1.9 3.5 -7.4 -1.5 2.2 3.8 6.0 -9.3 -2.9 2.0 4.0 5.1 -6.5 -2.7 2.4 4.1 5.1 -6.3  40° -3.8 2.2 3.8 7.2 -3.8 -1.6 -0.2 3.6 3.2 -9.1 -2.7 -0.4 1.3 2.9 -7.1 -1.3 2.4 3.9 6.6 -8.4 -2.9 2.3 3.6 6.3 -6.6 -2.9 2.3 3.6 4.5 -6.4  Radial slice 45° 50° -2.4 -1.8 1.2 1.4 4.7 3.7 7.8 6.7 -7.0 -5.8 -1.5 -3.0 1.6 1.6 3.7 4.1 4.6 7.0 -9.4 -9.3 -2.3 -2.4 -0.3 -0.8 3.6 4.5 3.6 3.2 -6.4 -5.4 -1.1 -0.9 1.8 2.9 4.5 5.1 6.5 6.8 -8.7 -8.0 -3.0 -3.4 2.7 2.8 4.1 3.4 5.7 6.6 -7.0 -8.2 -2.6 -2.9 1.9 0.6 4.1 2.5 4.9 4.1 -6.0 -7.5  Max 55° -0.5 1.3 3.4 5.8 -4.6 -2.5 2.1 4.9 6.4 -9.5 -3.3 -0.6 4.5 3.7 -5.0 -1.2 2.9 5.2 7.3 -7.3 -3.5 3.9 3.2 6.5 -8.0 -2.8 0.2 1.8 3.8 -6.8  60° -2.5 1.6 3.3 6.5 -4.9 -2.9 2.2 4.4 6.6 -10.5 -3.0 -1.0 4.3 3.6 -7.2 -1.3 2.7 4.7 6.0 -7.6 -2.8 3.6 3.4 5.4 -8.4 -2.7 0.1 1.9 3.2 -4.8  65° -2.4 1.6 2.9 4.5 -6.8 -2.2 2.5 4.8 7.3 -9.6 -4.0 -1.1 4.7 2.5 -6.1 -1.2 3.6 4.8 5.7 -8.7 -2.4 2.5 3.3 5.7 -9.0 -2.8 0.2 1.6 2.8 -7.2  70° -2.4 1.5 2.2 5.7 -7.0 -2.8 1.9 4.1 6.2 -11.2 -3.3 -0.4 4.1 4.2 -6.4 -0.8 3.4 4.3 4.6 -8.6 -3.0 2.7 2.9 5.7 -7.2 -3.5 -0.6 0.5 -2.9 -4.7  75° -1.1 0.8 2.5 3.9 -7.3 -3.5 1.3 4.4 4.0 -9.5 -3.8 -1.2 3.5 3.8 -7.7 -2.4 4.3 4.2 3.4 -8.3 -3.6 2.2 3.7 5.0 -8.8 -2.8 -0.6 -0.5 -4.0 -6.0  80° -3.2 1.3 1.2 2.6 -7.2 -3.7 1.7 3.7 1.3 -11.2 -2.6 -0.4 4.4 3.0 -7.6 -2.4 2.7 3.7 3.2 -9.2 -4.8 2.2 2.0 4.9 -8.6 -2.8 -2.2 -3.5 -2.4 -5.0  85° -2.2 -0.5 0.7 2.2 -7.9 -4.3 -2.2 2.9 -2.4 -11.5 -3.3 -0.4 2.5 3.4 -7.7 -2.5 0.3 3.2 2.2 -8.5 -3.6 1.3 0.1 3.5 -8.3 -3.3 -2.6 -3.1 -2.9 -5.9  90° -3.0 -2.7 -2.4 1.8 -8.2 -4.7 -3.9 3.4 -1.0 -9.4 -2.8 -0.3 0.9 3.0 -8.3 -2.4 -2.8 1.6 -2.5 -8.7 -3.7 -0.1 -2.7 1.9 -8.9 -2.9 -3.1 -1.8 -2.8 -5.1  -0.5 3.5 4.9 7.8 -3.8 -1.5 2.5 4.9 7.3 -3.2 -2.3 -0.3 4.7 4.2 -5.0 0.1 4.3 5.2 7.3 -7.3 -1.1 3.9 4.2 6.6 -3.3 -2.1 2.5 4.1 5.4 -4.7  Table F-2: Summary of triangular index measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given.  172  Specimen 1  2  3  4  5  6  Deformity Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected Native Deformity 1 Deformity 2 Deformity 3 Resected  0° 0.28 0.28 0.32 0.31 0.36 0.25 0.35 0.21 0.30 0.24 0.33 0.29 0.30 0.32 0.33 0.26 0.18 0.15 0.12 0.33 -0.01 0.20 0.19 0.11 0.32 0.35 -0.03 -0.06 -0.11 0.39  5° 0.26 0.27 0.28 0.29 0.33 0.21 0.29 0.19 0.21 0.20 0.36 0.22 0.27 0.18 0.29 0.25 0.17 0.16 0.09 0.34 0.01 0.16 0.12 0.10 0.27 0.32 -0.02 -0.14 -0.11 0.35  10° 0.25 0.26 0.23 0.36 0.28 0.23 0.26 0.10 0.23 0.18 0.32 0.27 0.34 0.01 0.30 0.25 0.15 0.08 -0.05 0.30 -0.01 0.13 0.07 0.08 0.23 0.32 -0.06 -0.16 -0.14 0.36  15° 0.27 0.05 0.21 0.24 0.31 0.19 0.24 0.05 0.16 0.18 0.34 0.30 0.29 -0.04 0.32 0.15 0.00 0.02 -0.12 0.30 -0.06 0.03 -0.07 -0.13 0.23 0.31 -0.06 -0.15 -0.12 0.33  20° 0.20 -0.02 -0.11 0.13 0.34 0.14 0.13 -0.02 0.12 0.10 0.32 0.17 0.19 -0.13 0.34 0.17 -0.07 -0.11 -0.15 0.33 -0.06 -0.08 -0.13 -0.24 0.22 0.28 -0.09 -0.13 -0.17 0.35  25° 0.25 -0.03 -0.16 0.11 0.34 0.16 0.08 -0.09 0.01 0.18 0.30 0.08 0.05 -0.14 0.31 0.13 -0.10 -0.08 -0.12 0.29 -0.03 -0.09 -0.14 -0.26 0.27 0.27 -0.10 -0.12 -0.19 0.34  30° 0.25 -0.03 -0.16 -0.20 0.32 0.16 0.06 -0.14 -0.08 0.14 0.31 0.05 -0.07 -0.17 0.32 0.12 -0.11 -0.10 -0.14 0.31 -0.07 -0.11 -0.15 -0.24 0.31 0.30 -0.08 -0.13 -0.17 0.35  35° 0.21 -0.07 -0.14 -0.21 0.33 0.16 0.05 -0.09 -0.13 0.12 0.29 0.02 -0.08 -0.14 0.32 0.12 -0.11 -0.10 -0.14 0.32 -0.02 -0.13 -0.19 -0.26 0.27 0.27 -0.08 -0.12 -0.22 0.36  40° 0.10 -0.07 -0.15 -0.15 0.37 0.12 0.03 -0.12 -0.16 0.13 0.27 0.05 -0.03 -0.13 0.32 0.08 -0.08 -0.11 -0.18 0.28 0.02 -0.15 -0.20 -0.27 0.27 0.31 -0.06 -0.13 -0.16 0.37  Radial slice 45° 50° 0.05 0.07 -0.05 -0.02 -0.16 -0.14 -0.08 -0.09 0.37 0.39 0.07 0.10 -0.01 -0.03 -0.14 -0.15 -0.16 -0.14 0.11 0.05 0.24 0.23 0.04 0.06 -0.10 -0.08 -0.02 0.02 0.31 0.29 0.09 0.07 -0.11 -0.10 -0.08 -0.11 -0.18 -0.18 0.30 0.32 -0.02 0.05 -0.16 -0.16 -0.14 -0.15 -0.24 -0.24 0.30 0.31 0.26 0.27 -0.06 -0.02 -0.10 -0.04 -0.19 -0.13 0.35 0.35  Min 55° 0.12 -0.01 -0.12 -0.07 0.32 0.12 -0.01 -0.15 -0.22 -0.01 0.22 0.08 -0.10 0.01 0.28 0.06 -0.10 -0.13 -0.18 0.33 0.04 -0.12 -0.12 -0.20 0.30 0.33 0.03 -0.03 -0.12 0.36  60° 0.10 0.03 -0.18 -0.09 0.31 0.11 -0.01 -0.16 -0.21 -0.03 0.23 0.08 -0.09 0.02 0.26 0.03 -0.10 -0.13 -0.15 0.30 0.04 -0.10 -0.11 -0.19 0.34 0.32 0.08 -0.02 -0.11 0.35  65° 0.12 0.04 -0.07 -0.07 0.33 0.10 0.00 -0.18 -0.21 -0.01 0.29 0.08 -0.07 -0.05 0.27 0.00 -0.10 -0.12 -0.16 0.36 0.02 -0.09 -0.10 -0.14 0.37 0.28 0.07 0.01 -0.09 0.36  70° 0.14 0.05 -0.07 -0.08 0.31 0.10 -0.02 -0.16 -0.21 -0.01 0.33 0.10 -0.07 0.02 0.26 0.00 -0.13 -0.11 -0.13 0.33 0.01 -0.06 -0.11 -0.13 0.37 0.30 0.13 0.03 0.19 0.35  75° 0.14 0.05 -0.02 -0.07 0.29 0.12 0.00 -0.15 -0.20 0.01 0.30 0.11 -0.07 -0.04 0.27 0.05 -0.07 -0.11 -0.09 0.33 0.07 -0.04 -0.08 -0.15 0.36 0.32 0.12 0.12 0.25 0.33  80° 0.13 0.09 -0.02 -0.04 0.30 0.16 0.01 -0.15 -0.11 0.01 0.33 0.16 -0.05 -0.05 0.26 0.04 -0.08 -0.10 -0.08 0.35 0.07 -0.01 -0.04 -0.15 0.38 0.29 0.15 0.32 0.31 0.32  85° 0.19 0.17 0.15 -0.03 0.32 0.21 0.08 -0.14 0.01 0.03 0.32 0.12 0.01 -0.06 0.28 0.06 -0.03 -0.07 -0.07 0.34 0.04 0.01 -0.02 -0.10 0.40 0.26 0.27 0.31 0.27 0.33  90° 0.12 0.17 0.14 -0.02 0.31 0.19 0.13 -0.10 0.07 0.08 0.32 0.16 -0.01 -0.01 0.24 0.08 0.14 -0.05 -0.01 0.31 0.05 0.03 0.08 -0.06 0.38 0.27 0.27 0.30 0.29 0.34  0.28 0.28 0.32 0.36 0.39 0.25 0.35 0.21 0.30 0.24 0.36 0.30 0.34 0.32 0.34 0.26 0.18 0.16 0.12 0.36 0.07 0.20 0.19 0.11 0.40 0.35 0.27 0.32 0.31 0.39  Table F-3: Summary of offset ratio measurements. 0° radial slice corresponds to superior; 90° radial slice corresponds to anterior. The average of three measurements is given.  173  

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