Summary

Posterior and combined-type shoulder instability is more common in military patients when compared to civilian populations and is less likely to present with diagnostic physical exam or MRI findings.

Abstract

Background

Increased frequency of posterior and combined shoulder instability in the active-
duty military population has been previously described; however, there exists large variations in
reported frequency and etiology. Additionally, posterior and combined-type instability are
known to present with more variable physical exam and imaging findings when compared to
anterior instability.

Purpose

The purpose of this study is to describe the epidemiology and etiology of surgically
treated shoulder instability within a large, single center cohort of active-duty military patients.
Additionally, we sought to compare imaging and clinical exam findings, as well as post-
operative medical discharge and re-operation rates between patients undergoing stabilization
surgery for anterior, posterior, and combined-type instability.

Methods

A retrospective review was conducted of patients treated surgically for shoulder
instability from a single military base during a ten-year period. Each case was characterized as
isolated anterior, isolated posterior, or combined, according to arthroscopic findings. Information
was collected on patient demographics, history of trauma, time to surgery, associated
pathological findings, and survivorship at minimum two years follow-up.

Results

A consecutive series of 416 patients (394 men, 22 women) underwent primary shoulder
stabilization surgery from January 2010 to December 2019. There were 158 patients (38%) with
isolated anterior instability, 139 (33%) with isolated posterior instability, and 119 (29%) with
combined instability. The mean patient age was 29.1 years. History of trauma was more
prevalent with isolated anterior instability (129, 81.7%) than with either isolated posterior
instability (95, 68.4%) or combined instability (73, 61.3%) (p=.047 and p=.001, respectively).
There were no significant differences in the rates of medical discharge or revision procedures between groups.

Conclusions

The findings of this study suggest that young, active-duty military patients are at
increased risk for isolated posterior and combined-type shoulder instability when compared to
civilian patient populations. Additionally, patients with posterior and combined-type instability
are less likely to have diagnostic physical exam or MRI findings than patients with anterior
instability. Orthopaedic surgeons should maintain a high index of suspicion for instability when
evaluating and treating young, active military patients who present with shoulder pain, even in
the absence of diagnostic physical exam or imaging findings.