Multiple Instability Events at Initial Presentation Are the Major Predictor of Failure of Nonoperative Treatment for Anterior Shoulder Instability

Purpose: To define the success rate of initial nonoperative treatment for traumatic anterior shoulder instability in a defined U.S. geographic population, describe factors that predict conversion to surgery after initial nonoperative management, and describe the long-term outcomes of nonoperative treatment after the index traumatic anterior instability event. Methods: The Rochester Epidemiology Project database was used to identify patients aged 14 to 39 years treated for anterior shoulder instability between 1994 and 2016. Patient demographic characteristics, comorbidities, injury characteristics, and imaging were evaluated. Patients treated nonoperatively for the first 6 months after the index instability event were analyzed to determine long-term outcomes (recurrence rate, pain at last follow-up, radiographic outcomes), the success rate of continued nonoperative treatment (no conversion to surgery), and factors associated with conversion to surgery (patient and injury characteristics). Survivorship free of surgery was reported with a Kaplan-Meier survival curve, and Cox proportional hazards models were used to evaluate association of variables with conversion to surgery. Results: A total of 379 patients met the study criteria, with an average follow-up period of 10.2 years (range, 0.53-25.00 years). The average age was 23.9 years, the mean body mass index was 26.2, and 100% of instability events were due to trauma. Of the shoulders, 79 (20.1%) ultimately failed initial nonoperative treatment and progressed to surgery. At final follow-up, the rate of recurrent instability was 52.3% in the group treated definitively without surgery, and the recurrence rate decreased from 92.4% to 10.1% in patients who underwent conversion to surgical treatment. Factors associated with conversion to surgery included 2 or more subluxations prior to the first evaluation (hazard ratio [HR], 1.82; P=.002), 2 or more dislocations prior to the first evaluation (HR, 1.76; P=.006), and recurrent instability at follow-up (HR, 4.21; P<.001). Conclusions: Most patients younger than 40 years with shoulder instability who were initially treated nonoperatively for 6 months were definitively treated without surgery. Ultimately, 35% of these patients experienced recurrent dislocations after 6 months of conservative treatment and 20% underwent surgical treatment. In most patients who underwent conversion to surgical treatment, surgery was performed within 12.5 years of their first instability event. Patients who experienced multiple instability events before or after consultation were more likely to undergo conversion to surgery after initial nonoperative management.