# Assessing contributions of muscular imbalance to shoulder osteoarthritis

> **NIH NIH F31** · NORTHWESTERN UNIVERSITY · 2020 · $45,520

## Abstract

PROJECT SUMMARY
Shoulder osteoarthritis (OA) is a common shoulder pathology that primarily affects older individuals. In the
setting of shoulder OA, the soft-tissue padding within the joint wears down resulting in bone-on-bone contact,
which causes inflammation and pain. The resulting pain can be debilitating, limiting daily living and work
activities. Treatment for end-stage disease involves total shoulder arthroplasty (TSA), in which the worn, bony
surfaces are replaced with prosthetic implants. In shoulder OA, bony erosion occurs symmetrically (concentric
deformity) or asymmetrically (eccentric deformity) about the glenoid center. Individuals with eccentric bony
deformities who undergo TSA face higher rates of implant failure requiring a revision surgery when compared
to the overall TSA population. Revision surgery is costly and results in increased complications and inferior
patient outcomes. To date, it has been proposed that the increased revision rates result from inadequate
correction of bony deformities; however, advances in surgical technique have not reduced failure rates. A
recent clinical theory is that imbalances between agonist and antagonist rotator cuff muscles contribute to bony
deformity development and persist following surgery. While this is a novel hypothesis, research has yet to
comprehensively quantify muscular balance in individuals with eccentric and concentric deformities prior to and
following TSA. This proposal will focus on identifying differences in muscular balance between individuals with
concentric and eccentric deformities prior to and following TSA by quantifying strength balance (relative
strength in various directions) in individuals with shoulder OA. Further, this work will evaluate the two main
determinants of muscle strength: muscle activation and muscle volume. Aim 1 will quantify three-dimensional
strength balance across the shoulder in multiple directions during maximal isometric torque production. Aim 2
will quantify shoulder muscle activation (extent to which nervous system can access muscles’ full capacity)
during submaximal isometric torque production. This aim will also quantify rotator cuff muscle volume,
adjusting for muscle degeneration, which serves as an indirect measure of muscle capacity. Strength, muscle
activation, and muscle volume will be assessed in individuals with concentric and eccentric bony deformities
cross-sectionally prior to and following TSA. For Aim 1, a six degree-of-freedom load cell will be used to
measure three-dimensional shoulder torque. For Aim 2, surface and intramuscular electromyography will be
used to measure muscle activity about the shoulder. Muscle volume and intramuscular fat will be computed
from magnetic resonance images. The results of this work will provide the first quantitative comparison of
muscular balance in individuals with concentric and eccentric bony deformities prior to and following TSA. The
findings will directly inform current management of ind...

## Key facts

- **NIH application ID:** 9992633
- **Project number:** 1F31AR077426-01
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Margaret Coats-Thomas
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $45,520
- **Award type:** 1
- **Project period:** 2020-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9992633

## Citation

> US National Institutes of Health, RePORTER application 9992633, Assessing contributions of muscular imbalance to shoulder osteoarthritis (1F31AR077426-01). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9992633. Licensed CC0.

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