Secular trend of adhesive capsulitis

Abstract

Adhesive capsulitis (AC) is a painful shoulder disorder resulting in restrictions of daily activities. Given the recent increase in risk factors for AC, such as diabetes mellitus, research is needed to examine if the incidence of AC has also increased. Therefore, the purpose of this study was to describe the secular trend of AC. Subjects were from The Health Improvement Network, an electronic medical record database of general practices across the UK from 1995-2008. General practitioners diagnosed AC. We included subjects ages 40-79 years and defined an incident case as the first diagnosis of AC following at least 1 year of enrollment in the database. We examined the potential independent effects of age, calendar time, and birth cohort using an age-period-cohort model. To approximate effect estimates, we applied proportional hazards models and separately adjusted for diabetes mellitus. Of 2,188,958 subjects (50.0% women), the incidence of AC was 2.36 and 3.38 per 1,000 person-years for men and women, respectively. Age-period-cohort model graphs suggested a secular trend due to a birth cohort, but not calendar effect. For each 10-year increment in birth cohort, the incidence rate increased by 8% in women (hazard ratio 1.08, 95% confidence interval 1.05-1.13). There was no increase in AC incidence for men. Adjusting for diabetes mellitus did not change these associations materially. We found women born more recently are at a higher risk of developing AC compared with women born earlier. Future research is needed to identify risk factors that may be responsible for this increase.