Exploring the Link between Metformin Use and Adhesive Capsulitis of the Shoulder: a retrospective cohort study in Taiwan 

AbstractObjective The risk of adhesive capsulitis of shoulder in diabetic patients taking metformin has not been evaluated. We aimed for evaluating the relative risk of adhesive capsulitis of shoulder in diabetic patients taking metformin at the level of the whole country population. Methods We conducted a retrospective cohort study using a national health insurance database in Taiwan from 2000 to 2013. We used International Classification of Diseases, Ninth Revision, to categorise the medical condition for study group and comparison group. We used Cox proportional hazard regression analyses to determined adjusted hazard ratios (aHRs) of adhesive capsulitis of shoulder between study and comparison group after adjusting for sex, age and comorbidities. Results Among 13863 diabetic patients using metformin, 1294 patients were diagnosis with adhesive capsulitis of shoulder during follow up. Of the 55452 patients without the use of metformin, 5227 patients developed adhesive capsulitis of shoulder. Adhesive capsulitis of shoulder risk was elevated in patients taking metformin than in non-metformin group (adjusted hazard ratio [HR] 1.064, 95% confidence interval [95% CI] 1.000 to 1.321; p = 0.048). Conclusions Risk of adhesive capsulitis of shoulder among the diabetic patients taking metformin was higher than those did not taking metformin. It indicated that metformin may cause fibrosis in joint capsule.