Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Mechanical and Materials Engineering
Supervisor
Ferreira, Louis M.
Abstract
The shoulder is highly unconstrained and is susceptible to injury and disease. While shoulder injuries and pathologies are common, their effects on joint biomechanics are not well understood. Ex-vivo simulators allow shoulder biomechanics to be studied in controlled environments to improve our understanding of shoulder function. To date, the most sophisticated simulators only perform simple planar motions at quasi-static speeds, limiting their utility. The aim of this research was to develop and validate a shoulder motion simulator capable of multiplanar motion at elevated speeds.
The developed simulator used an iterative learning tendon excursion control architecture with open-loop execution and independent muscle control to perform multiplanar motion at elevated speeds. Motion tracking errors were below 1.5° and the observed muscle force relationships were consistent with previous literature. Following its validation, the simulator was used in a number of biomechanical studies.
The first study measured surface strains along the scapular spine and acromion in the native shoulder and showed that surface strains were significantly affected by the deltoid load vector. The second study mapped the three-dimensional moment arms of eight major muscles across a multiplanar range of motion and showed that the muscles in the shoulder had multi-dimensional functions that changed with joint orientation. Study three investigated the effect of rotator cuff deactivation pattern on shoulder function. Consistent with existing clinical data, deactivation patterns involving three tendons resulted in functional deficits while all deactivation patterns were associated with increases in deltoid force and scapula strain. The final study investigated the effect of humeral offset on reverse total shoulder arthroplasty biomechanics. While humeral offset had a significant effect on muscle function and scapula strains, it did not influence joint compression or centre of pressure.
This research represents a significant advancement in ex-vivo simulation technology. It encompasses the development of a novel iterative learning control architecture capable of faster and more complex motions than has been previously reported. The studies conducted in this work have expanded our understanding of shoulder biomechanics and the developed simulator will continue to assist researchers and clinicians in improving patient outcomes.
Summary for Lay Audience
The shoulder has an extensive range of motion that enables us to position our hand in space and interact with our surroundings. However, this versatility in movement comes at the expense of stability and makes the shoulder susceptible to injury and disease. Despite their prevalence, the causes of shoulder injury and disease are often not well understood, and the implications of treatment are often unclear. While shoulder function can be studied in a living person, there are many factors that cannot be controlled, and the techniques used to measure many of the parameters of interest are too invasive to be used in a living subject. Therefore, researchers have developed alternative techniques to study the shoulder and its function in controlled environments.
One tool that researchers use is a shoulder motion simulator. These devices use shoulder tissue obtained from deceased donors to mimic the shoulder movements of a living person by pulling on muscles in the shoulder using computer-controlled motors. While many simulators have been developed, they are limited to performing very simple movements at slow speeds. This is problematic because many of the movements we perform during everyday tasks are not only complex but also involve high speeds. Therefore, the aim of this research was to develop a new shoulder motion simulator that could simulate complex movements with elevated speeds.
This research begins with the development and performance evaluation of a new shoulder motion simulator. The simulator was highly accurate at performing more complex motions with higher speeds than any existing simulator. Following its development, the simulator was used to investigate different clinically relevant questions to better understand healthy shoulder function as well as the impact of injury and surgical treatment on shoulder motion, muscle and joint forces, and the stresses placed on critical bone structures.
This research represents a significant advancement in the field of shoulder motion simulation technology. The investigations carried out in this thesis have improved our understanding of shoulder function and the simulator will continue to be implemented in future investigations aiming to improve the quality of treatment for patients.
Recommended Citation
Axford, David, "Development of an Iterative Learning Control Architecture to Evaluate Ex-Vivo Shoulder Biomechanics During Simulated Active Motion" (2024). Electronic Thesis and Dissertation Repository. 10285.
https://ir.lib.uwo.ca/etd/10285
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