Shoulder (glenohumeral joint) osteoarthritis causes pain, limits daily activities, and frequently requires joint replacement surgery. In shoulder osteoarthritis, the glenoid bone surface erodes in one of two ways: symmetrically (concentric deformity) or asymmetrically (eccentric deformity). Shoulder replacements in patients with eccentric deformities fail and require additional, revision surgery more often than replacements in patients with concentric deformities. These failures are thought to result from imbalances between the anterior and posterior rotator cuff muscles, which surround and stabilize the shoulder, specifically with posterior deficiency. Muscle deficiency in the posterior rotator cuff would manifest functionally as relative weakness; however, strength has not been evaluated and compared between patients with eccentric and concentric deformities. Furthermore, clinical strength measurement tools may be limited to detect imbalances. In this thesis, I addressed these gaps by first comparing clinical and laboratory tools for assessing strength. I then used laboratory tools to quantify and compare strength, along with its determinants, muscle size and activity, between patients with eccentric and concentric deformities. When comparing laboratory three-dimensional methods and clinical one-dimensional methods for measuring strength, I found that one-dimensional measurements overestimate strength due to greater off-axis torque generation. Given these results, I evaluated three-dimensional strength in patients before surgery, as well as rotator cuff muscle size, but found no differences between deformity groups. A remaining unknown was whether strength or muscle activity deficiencies exist following surgery in patients with pre-operative eccentric deformities. Therefore, I quantified three-dimensional strength and muscle activity in patients after shoulder replacement. While strength was reduced in patients following surgery compared to healthy adults, it did not differ by deformity type. However, patients with eccentric deformities demonstrated reduced posterior rotator cuff muscle activity, suggestive of a posterior deficiency that may be related to post-operative failures. Together, this work characterized three-dimensional strength and its determinants in patients with shoulder osteoarthritis, providing important insight into mechanisms that potentially contribute to shoulder replacement failures.

Creator

• Coats-Thomas, Margaret Sarah

DOI

• https://doi.org/10.21985/n2-0v7s-8b86

Subject

• Biomedical engineering
• Biomechanics

Language

• en

Alternate Identifier

• etdadmin_upload_913153
• http://dissertations.umi.com/northwestern:16136

Keyword

• Shoulder osteoarthritis
• Arthroplasty
• Rotator cuff

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright