UBC Theses and Dissertations
Measurement of three-dimensional scapular kinematics Choo, Anthony Min Te
It has been well recognized that the scapula and the humerus work in concert to enable the shoulder joint to achieve its high mobility in three-dimensions. Pathologies such as impingement and instability are focused at the glenohumeral junction between the two bones. Other authors have attempted to measure scapulothoracic and scapulohumeral rhythms as a means of better understanding the shoulder joint. However, at present, the inability to practically measure scapular kinematics in a clinical setting constitutes a significant problem in the rehabilitation of shoulder pathologies. This thesis addresses the issue of measuring three-dimensional scapular kinematics non-invasively. A novel method using a grid of skin surface markers was developed. The method was found to show promising results in a pilot study and a pre-clinical test on a cadaver. An accuracy of better than 5° was achieved for all three cardan angles used to describe changes in scapular attitudes. The method quantified the regional variations encountered with surface markers and identified the optimal regions for measurement. Additionally, a prototype method utilizing two-dimensional Fourier analysis was investigated to measure scapular upward rotation through image analysis of surface features. The results were not conclusive but merit further investigation. The gold standard used to assess accuracy of the non-invasive method was roentgen stereophotogrammetric analysis (RSA). The accuracy of the RSA system was investigated with computer simulations and benchtop analyses. System accuracy ranged from 0.21-mm to 0.67-mm for reconstruction of marker coordinates, from 0.23- mm to 0.86-mm for translation, and from 0.19° to 1.05° for rotations. The stereophotogrammetric calibration method was an important factor in the resultant accuracy. The accuracy was also affected by the reconstruction algorithm used. Direct Linear Transformation (DLT) was found more favorable than traditional RSA methods described by Selvik. Finally, low x-ray scanning resolution (150-ppi) was a principal hardware limitation contributing to lower accuracy. This thesis has demonstrated a scapular measurement technique and presented some novel ideas that should contribute to the long-term development of a clinically practical, non-invasive, accurate method for measuring human scapular kinematics.
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