The Epidemiology of Primary Anterior Shoulder Dislocations in Patients Aged 10-16 Years and Age-Stratified Risk of Recurrence

OBJECTIVES: Most clinical studies pertaining to shoulder dislocation use age cutoffs of 16 years, and at present, only small case series of patients aged 10-16 years guide our management. Using a general population cohort aged 10 to 16 years, we sought to: 1) determine the overall and demographic-specific incidence density rate (IDR) of primary anterior shoulder dislocation requiring closed reduction (CR), and 2) determine the rate of and risk factors for repeat shoulder CR. METHODS: Using administrative databases, we identified all patients who underwent CR of a primary anterior shoulder dislocation by a physician in Ontario between April 2002 and September 2010 (the index event). Exclusion criteria included age (16 years), posterior dislocation, and prior shoulder dislocation or surgery. The IDR was calculated for the entire cohort and compared by age and sex subgroups. The main outcome, repeat shoulder CR, was sought until September 2012. A time-to-event analysis (cumulative incidence function) was used to determine the incidence of repeat shoulder CR at six-months, one-year, two-years, and five-years for the entire cohort and subgroups based on age (10-12, 13, 14, 15, and 16 years). A competing risk model identified risk factors for repeat shoulder CR, which were reported using hazard ratios (HR) with 95% confidence intervals (CI). RESULTS: We identified 2,066 patients aged 10-16 years who underwent CR following a primary anterior shoulder dislocation, of which, 1,937 met the exclusion criteria. The median age was 15.0 years and 79.7% were male. The IDR was 20.1 per 100,000 person-years, and was highest among 16 year-old males (164.4 per 100,000 person-years). In contrast, primary anterior shoulder dislocation was rare among patients aged 10-12 years [5.9% (N=115) of all primary dislocations]. Repeat shoulder CR was observed in 740 patients (38.2%) after a median of 0.8 years. The overall cumulative incidence of repeat shoulder CR at six-months, one-year, two-years, and five-years was 13.0%, 21.3%, 29.2%, and 36.2%, respectively; however, the cumulative incidence by age (Figure 1) revealed the rate of repeat shoulder CR to be highest among 14-16 year-olds (37.2-42.3%), and considerably less among patients aged 10-13 years (0-25.0%). Male sex (HR 1.2, p=0.04; interpreted as a 20% increased risk for males as compared to females) and patient age (HR 1.2, p<0.001; interpreted as a 20% increased risk for each year over age 10) significantly influenced the risk of a repeat shoulder CR. Overall, 31.2% (N=604) of patients underwent shoulder stabilization, of which, half underwent surgery following the index shoulder CR (49.9%, N=369). CONCLUSION: Primary anterior shoulder dislocations are common among 14-16 year olds, and the rate of recurrence in this age group following non-operative management mirrors that of 17-20 year olds in previously published data. In contrast, both the incidence of primary anterior dislocation and rate of recurrence are considerably lower for patients aged 10-13 years. Going forward, clinicians should treat and counsel patients aged 14-16 years, particularly males, as they do older adolescents (17-20 years); however, patients 13 years of age or younger should be counselled regarding their low risk for recurrence.