Epidemiology of Primary Shoulder Dislocations. A Cohort Study from a Large Health Maintenance Organization: 2004 to 2019

Background: Previous epidemiological studies on shoulder instability evaluated specific and relatively small subgroups of patients. Objectives: To determine the incidence rate of primary shoulder dislocations. Methods: Cohort analysis of electronic health records from 2004 to 2019 was conducted in a urban district of a major health maintenance organization (HMO) in Israel. Patients presented with primary shoulder dislocation that was treated with closed reduction in any medical facility within the district. Overall incidence density rates (IDR) of primary shoulder dislocations and stabilization surgeries were determined. Results: Over a period of 16 years 13,158 patients underwent closed reduction of primary shoulder dislocation. Of those, 712 shoulder stabilization surgeries were performed (5%). The IDR of primary shoulder dislocations were 124 per 100,000 person-years. The IDR of primary shoulder stabilizations were 7 per 100,000 person-years. The peak in the number of dislocations was observed in those 20-29 years old and > 60 years of age. In patients under 59 years old, dislocations were more common in men. In those > 60 years of age, dislocations were more common in women. Most shoulder stabilization surgeries were performed on young patients. The annual mean time from the first dislocation to stabilization surgery linearly declined to 6 months in 2019. Conclusions: The IDR of primary shoulder dislocations calculated from the largest HMO in Israel were 124 per 100,000 person-years. Shoulder dislocations had bimodal age distribution. Overall, 5% of the patients (mainly young) with shoulder dislocations underwent shoulder stabilization surgery during the study period.