Posterior Shoulder Instability High in U.S. Military

The incidence of posterior shoulder instability in U.S. military members is higher than previously reported, according to a new study.

The researchers wrote, “Relatively little is known about the true incidence of posterior shoulder instability in the United States. The purpose of this study was to characterize the incidence of posterior shoulder instability in the U.S. military population and to examine which characteristics place these patients at highest risk.”

In this descriptive epidemiology study, “Incidence of Posterior Shoulder Instability in the United States Military Demographic Considerations From a High-Risk Population,” published on December 2, 2020 in The American Journal of Sports Medicine, the researchers analyzed cases of posterior shoulder dislocation and subluxation in the Defense Medicine Epidemiology Database.

The cases were from between 2016 and 2018. Incidences were calculated, and multivariate Poisson regression was used to calculate adjusted rate ratios for the effects of sex, race, age, military service branch, rank, and year.

According to the data collected, the overall unadjusted incidence was 0.032 per 1,000 person-years for posterior dislocations, 0.064 per 1,000 person-years for posterior subluxations, and 0.096 per 1,000 person-years for all cases of posterior shoulder instability.

The total incidence of all shoulder instability was 1.84 per 1,000 person-years, with posterior shoulder instability accounting for 5.2% of total cases.

For posterior subluxation, there were significant differences between groups in both unadjusted and adjusted rate ration (ARR) for sex (ARR, 3.31; 95% CI, 1.85-5.93 for men), race (ARR, 0.458; 95% CI, 0.294-0.714 for Black service members and ARR, 0.632; 95% CI, 0.421-0.948 for service members of other races), age (ARR, 3.69; 95% CI, 1.56-8.70 for patients aged 30-34 years), and military service branch (ARR, 0.663; 95% CI, 0.460-0.955 for Air Force service members).

For posterior shoulder dislocations, there was only a significant difference between men and women (ARR, 4.55; 95% CI, 1.85-11.2 for men).

“The incidence of posterior shoulder instability among U.S. military personnel is higher than previously reported in the general U.S. population, with a majority of cases due to subluxation. This increased incidence is likely reflective of a young and highly active population along with improvements in awareness and diagnosis of posterior instability in recent years,” the authors wrote.