Development of Four-Dimensional Computed Tomography Based Methods to Measure Shoulder Kinematics in Healthy Individuals and in Patients following Total Shoulder Arthroplasty
Abstract
Dynamic kinematics of the shoulder, particularly the interplay between the glenohumeral and scapulothoracic joints and the changes associated with aging, remain not fully understood. Current research often focuses on simple motions, neglecting more complex movements common in activities of daily living, such as internal rotation to reach behind the back. Post-total shoulder arthroplasty (TSA) surgery, many patients experience difficulties with internal rotation, affecting tasks like dressing and bathing. This dissertation employs four-dimensional computed tomography (4DCT) to enhance understanding of shoulder biomechanics and TSA outcomes by assessing dynamic shoulder kinematics in a healthy population and a post-implant population.
The first objective was to develop and validate a process for measuring dynamic glenohumeral and scapulothoracic kinematics via 4DCT. This process uses a single vertebra as a reference for scapulothoracic motion and demonstrated satisfactory repeatability. The next objective was to improve its feasibility by automating bone model segmentation from scans. This consisted of creating convolutional neural networks for the humerus and scapula, achieving human-comparable accuracy in a fraction of the time.
The developed techniques were then utilized to quantify healthy shoulder kinematics and the impact of aging. The importance of humeral translation was confirmed, as all participants exhibited some degree of translation. Older participants showed less humeral motion, predominantly humeral translation, although scapulohumeral rhythm remained unchanged relative to the younger participants. The results also revealed age-related alterations in bone positioning, including increased lateral rotation, posterior tilting, and superior translation of the scapula. The altered pose also affected the range of motion of the scapula.
Finally, kinematics between natural and anatomic TSA shoulders were compared, examining the effects of mobility and implant mismatch. The hypothesis that patients with good mobility would exhibit similar kinematics to non-implant participants was unsupported; the good mobility group showed significant differences compared to healthy controls, notably, greater humeral translation. Furthermore, regardless of mobility, all implant patients had limited humeral internal rotation, compensated by increased humeral extension. No correlation between implant mismatch and range of motion was found, indicating that mismatch does not significantly affect shoulder kinematics.