Incidence of and Risk Factors for Glenohumeral Osteoarthritis following Anterior Shoulder Instability: A U.S. Population-Based Study with an Average 15-year Follow-up

OBJECTIVES: The rate of osteoarthritis (OA) in patients with anterior shoulder instability (ASI) varies within the literature, with the majority of studies investigating rates after surgical stabilization. ASI appears to lead to increased rates of OA, although risk factors for developing OA in non-operative and operative cohorts are not well defined. The purpose of this study was to determine the incidence of clinically symptomatic OA and identify potential risk factors for the development of OA following ASI in a U.S. geographic population of patients under the age of 40. METHODS: An established geographic database was used to identify patients less than 40 years old diagnosed with anterior should instability between 1994 and 2016. Patient information, including demographics, imaging and surgical details, was collected and comparative analysis was performed between groups with and without OA at final follow-up, as well as patients who underwent surgical and non-surgical management. RESULTS: The study population consisted of 154 patients with a mean follow-up of 15.2 years (range 5.1-29.8). Overall, 22.7% of patients developed clinically symptomatic glenohumeral OA. Twenty-eight percent of patients who underwent at least 1 surgical intervention and 17% of patients who underwent non-operative management of anterior shoulder instability developed glenohumeral OA (p=0.176). Patients who developed arthritis were older at initial instability event (p=0.002) and had higher BMI (p=0.007). Additionally, patients with OA were more likely to be current or former smokers (p=0.004), have a seizure disorder (p=0.033), and be manual laborers (p=0.044). Risk factors for developing OA included seizure disorders (RR 2.61, 95 % CI 1.34-5.07), cartilage injury on initial MRI (RR 2.48, (1.00-6.13), current or former smoker (RR 2.46, 95% CI 1.37-4.42), laborer occupation (RR 2.14, 95% CI 1.14-4.01), and age at initial instability event (OR 1.09 per year, 95% 1.03-1.17). Athletes (RR 0.51, 95% CI 1.08-3.54), specifically contact athletes at the time of initial instability (RR 0.45, 95% CI 0.21-0.97), were less likely to develop OA. There was no difference in the number of dislocations or number of instability events in patients with and without symptomatic osteoarthritis. CONCLUSIONS: In a U.S. geographic population of patients less than 40 years old with ASI, approximately one-fourth of patients developed symptomatic OA at a mean follow-up of 15 years from their first instability event. When accounting for differences in patient demographics, there was no significant difference in the rates of OA in patients who underwent surgical and non-surgical management. Overall, there was an increased risk for the development of OA in patients with seizure disorders, cartilage injury on initial MRI, current or former smokers, laborer occupation and increased age at the initial instability event.