Incidence of shoulder dislocations and the rate of recurrent instability in soldiers

Purpose Shoulder dislocations present a potentially debilitating injury for soldiers and other groups of physically active adults. The purpose of this study was to determine the 10-yr incidence rate of shoulder dislocations in soldiers, the percentage with recurrent instability, and risk factors for these injuries. Methods This retrospective cohort study used medical encounter data from U.S. Army soldiers to calculate the 10-yr incidence rate for shoulder dislocations and the percentage of chronic or recurrent injuries >3 months and ≤2 yr after the initial diagnosis. A Cox proportional hazards model was constructed using demographic variables (age, race, education level, marital status, and sex) to determine incidence rate ratios for risk factors related to shoulder dislocation. Logistic regression was used to calculate odds ratio for risk factors for recurrent injury, including concurrent diagnoses (brachial plexus or peripheral nerve injuries and fractures of the scapula or proximal humerus). Results There were 15,426 incident shoulder dislocations, with a 10-yr incidence rate of 3.13 per 1000 person-year. Soldiers ≤40 yr old showed greater risk for injury compared with those older than 40 yr. The incidence rate ratio for males compared with females was 1.64, 95% confidence interval = 1.55-1.74. Recurrent injury occurred in 28.7% of cases. Concurrent axillary nerve injury (odds ratio = 3.64, 95% confidence interval = 1.56-8.46) and age ≤35 yr were associated with greater risk of recurrence. Conclusion Within the active duty U.S. Army, men and younger individuals showed greater risk for shoulder dislocations. Over one-quarter of incident cases became recurrent. Axillary nerve injuries and younger age increased the odds of recurrent injury.