# Impact of Overload and Overuse Following Subscapularis Tears: Mechanisms of Shoulder Joint Damage

> **NIH VA I01** · PHILADELPHIA VA MEDICAL CENTER · 2022 · —

## Abstract

Rotator cuff tears affect millions of individuals each year in the United States, impacting
veterans and civilians alike. Tears dramatically alter joint mechanics leading to significant
damage to articular cartilage and adjacent (intact) tendons within the shoulder. This damage
leads to loss of function, pain, tear progression, and even tendon re-tear following repair.
Therefore, identifying mechanisms of joint damage after tendon tear is an active area of
research. We have previously discovered how joint damage occurs following supraspinatus and
infraspinatus tears using an in vivo rat rotator cuff tear model. These results altered clinical
practice by clearly demonstrating that loss of the anterior-posterior force couple leads to
permanent detrimental changes to the shoulder joint. While subscapularis tendon tears were
once thought to be uncommon, increased use of arthroscopy and improved imaging have led to
a dramatic increase in subscapularis tear diagnosis, specifically in ~ 50% of patients undergoing
rotator cuff repair. Furthermore, it has been suggested that unrecognized subscapularis tears
may be a source of chronic dysfunction and pain. However, no studies have examined the
critical question of how subscapularis tendon tears affect the shoulder joint, and as a result, a
clear best clinical approach has not been identified for this common and debilitating condition.
Therefore, the clinical objective of this work is to specifically determine the extent and
mechanisms of shoulder joint damage, functional alteration, and pain that result from rotator cuff
tears involving the subscapularis. We hypothesize that loss of the anterior-posterior force couple
after subscapularis tear leads to detrimental joint damage, loss of function, and pain, and that,
due to the critical role of the subscapularis, these effects are significantly increased when
compared to a supraspinatus tear alone. Additionally, we hypothesize that these detrimental
changes are exacerbated by joint overuse after tendon detachment.
Our well-characterized, controlled in vivo pre-clinical model system is ideal for the posed
questions. The hypotheses will be evaluated with a series of tendon detachments followed by
comprehensive combination of mechanical property measurements, tissue composition
measures, and longitudinal in vivo functional evaluation of joint kinematics, shoulder range of
motion, and grip strength of the affected limb, defining how in vivo changes are reflected in ex
vivo measurements. Experiments will be repeated with the addition of a treadmill overuse
protocol post-injury to identify the compounding effects of overuse after a tendon tear. The
proposed research will identify how subscapularis tears affect joint health and function, the
consequences of an undiagnosed tear, and the role of shoulder overuse after subscapularis tear
in intensifying these issues, while also providing important insights into chronic shoulder pain
and loss of function. Results from t...

## Key facts

- **NIH application ID:** 10534338
- **Project number:** 1I01RX003652-01A2
- **Recipient organization:** PHILADELPHIA VA MEDICAL CENTER
- **Principal Investigator:** Andrew Frederic Kuntz
- **Activity code:** I01 (R01, R21, SBIR, etc.)
- **Funding institute:** VA
- **Fiscal year:** 2022
- **Award amount:** —
- **Award type:** 1
- **Project period:** 2022-11-01 → 2026-10-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10534338

## Citation

> US National Institutes of Health, RePORTER application 10534338, Impact of Overload and Overuse Following Subscapularis Tears: Mechanisms of Shoulder Joint Damage (1I01RX003652-01A2). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10534338. Licensed CC0.

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