Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biomedical Engineering

Supervisor

Lalone, Emily A

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.

Summary for Lay Audience

Understanding movement in the shoulder, especially the scapula (shoulder blade), is still not fully clear, particularly how it changes as people age. Many studies focus on simple shoulder movements and overlook complex motions needed for daily activities, like reaching behind the back. After receiving a shoulder implant, patients often struggle with this motion, which is essential for tasks like dressing and bathing. This research uses advanced imaging, which can visualize the bones of the shoulder moving, to closely examine shoulder movements in both a healthy population and a post-implant population. The goal of this research is to improve understanding of shoulder function and surgical outcomes.

The first goal was to create a method to measure shoulder movements using this advanced imaging technology, and ensure this method is reliable, which was successfully done. The next goal was to speed up the process of analyzing these images by training a computer program to automatically identify and model the shoulder bones. This program proved to be as accurate as human experts and could complete the task much faster.

The third part of the research aimed to understand how healthy shoulders move, and how aging affects this movement. It was found that older participants had less sliding motion within the shoulder joint. Additionally, the scapula of older individuals was found to be positioned differently than the younger participants, which resulted in differences in how much the scapula had to move to achieve the same end position.

The final study compared the movements of participants with natural shoulders to participants who had received a shoulder implant. It was expected that patients with good motion post-surgery would have shoulder movements similar to those without implants, but this was not the case. Furthermore, all implant participants had restricted rotation of the upper arm, which they compensated for by increasing how much their arm moved backward. Lastly, no link was found between the size of an implant and shoulder motion.

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