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Immunohistochemistry and biomechanical properties of the non-pathological elbow joint capsule

University of British Columbia

One of the most important complications in elbow joint (EJ) pathology is posttraumatic contracture of soft tissues surrounding the joint. Insidious stiffness takes over the joint, decreasing the Range of Movement (ROM). Post-traumatic contracture of the EJ, with subsequent stiffening, is very often the result of contracture of the anterior capsule. However, despite the critical role it plays in the pathogenesis of the EJ contracture, very little is known about the structural and biomechanical properties of the EJ capsule. The type of collagen (notably type I and type III) and its organization in extracellular matrices plays a critical role in determining biomechanical properties (elasticity and structural stiffness) of biological structures. In order to determine whether there were changes in expression of the type of collagen, between normal and contracted post-traumatic EJ capsules (n=3), we performed immunohistochemical analysis. The results indicated that collagen type III was not expressed in capsules derived from cadavers (n=10) with no history of trauma to the EJ (within the limits of detection by fluorescence immunohistochemistry). In contrast, isles of collagen type III fibrils were detected in capsules from patients with contracted post-traumatic EJ (n=3). This observation supports the hypothesis that contracture of the EJ is associated with expression of collagen type III, which is not expressed in normal EJ capsules (in this age group). From these studies, we propose that expression of collagen type III in post-traumatic contracture of the EJ may lead to changes in biomechanical properties of the joint. This in turn may affect the ROM of the contracted EJ. We initiated studies to determine biomechanical properties of the EJ capsule. These initial studies were performed with non-pathological EJ capsules, in order to establish experimental protocols most appropriate for such studies. Moreover, although the nonpathological EJ capsule plays a critical role in stabilizing the elbow joint (while allowing physiological motion) there is no data in the literature that documents its biomechanical properties. Thus, our aim was to determine biomechanical properties (Modulus of Elasticity and Structural Stiffness) of normal elbow joint capsules. The anterior portion of ten non-pathological EJ capsules, were excised from fresh cadavers (aged 75 to 93 years) and cleaned of unrelated soft tissues, such as muscle and fat. The capsules were sectioned into 3 mm wide strips, producing a total of 87 samples. The samples were grouped according to their anatomical locations (radial, mid-capsular and ulnar regions). Each sample was loaded in tension at 1 mm/sec, to the stage of failure, in a servohydraulic materials testing machine (DynaMight, Instron, Canton, MA). The width and thickness were measured using callipers at 25%, 50% and 75% of the initial length. The cross sectional area was approximated as an ellipse and samples were coated with blue chalk, prior to testing, to determine the failure location. Structural stiffness was calculated from the linear region of the load-displacement curve and the intrinsic mechanical property, modulus of elasticity (Young's Modulus), was calculated using the initial cross-sectional area, closest to the point of failure (i.e. at 25%, 50% or 75%). A two-factor repeated measures ANOVA was performed to determine statistical significance for p less than 0.05. No significant statistical differences were found for Young's Modulus (p = .1536) or structural stiffness (p = .2) between the three different regions of the capsules. The mean Young's Modulus of the pooled samples was 17.7 MPa and the mean structural stiffness was 5.8 N/mm. Our studies are the first to evaluate Modulus of Elasticity and Structural Stiffness of normal EJ capsules. These results represent reference data for further comparison with biomechanical properties EJ capsules in pathological states, including post-traumatic contracture. Further studies would be useful to elucidate the correlations between induction of expression of collagen type III and change in biomechanical properties of the E J capsule. Revelation of an association between these two parameters may lead to novel methods of prevention and/or treatment of decreased ROM of joints due to trauma (either through accidents, vocation or sports) or as a result of diseases associated with inflammation of joints and/or aging (such as rheumatoid arthritis and osteoarthritis). i

Thesis/Dissertation

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2009-11-25

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http://hdl.handle.net/2429/15773

Animal Science

University of British Columbia

UBCV

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