Association between body mass index and incident shoulder adhesive capsulitis in Germany: A retrospective cohort study of 522,830 adults

OBJECTIVES: Little data exists on the effects of body mass index on the incidence of shoulder adhesive capsulitis. This study investigated the association between body mass index and incident adhesive capsulitis in Germany. STUDY DESIGN: Retrospective analysis of data from 522,830 adults in 677 general practices in Germany over the period 2005-2023. MAIN OUTCOME MEASURES: The index date corresponded to the first documentation of body mass index. The diagnosis of shoulder adhesive capsulitis was assessed in the 10 years following the index date using the International Classification of Diseases, 10th revision. Participants were aged ≥18 years at the index date, had an observation period of at least 12 months prior to the index date, and had no history of adhesive capsulitis prior to or at the index date. Associations were studied using Kaplan-Meier curves and Cox regression analyses. RESULTS: The mean (standard deviation) age of the population was 53.5 (17.3) years, while the proportion of women was 53.1%. The 10-year cumulative incidence of adhesive capsulitis was 0.63%, 0.65%, 1.05%, and 1.25% in people with underweight, normal weight, overweight, and obesity, respectively (p <0.001). These associations were corroborated in the adjusted Cox regression analyses focusing on categorical body mass index (normal weight reference; underweight hazard ratio 0.92 [95% confidence interval 0.68-1.26]; overweight hazard ratio 1.52 [1.39-1.67]; obesity hazard ratio 1.77 [1.61-1.95]) and continuous body mass index (1.03 [1.02-1.04]). CONCLUSIONS: Overweight and obesity were associated with an increased risk of adhesive capsulitis. More data are needed on the mediating factors involved in the relationship between body mass index and adhesive capsulitis.