Objective
We evaluated the incidence rate and factors associated with fractures among adults with ankylosing spondylitis (AS).

Methods
We performed a retrospective cohort study with data from the Rheumatology Informatics System for Effectiveness (RISE) registry linked to Medicare claims from 2016-2018. Patients were required to have two AS ICD codes, ≥30 days apart, and a subsequent Medicare claim. Then, one year of baseline characteristics were included, after which patients were observed for fractures. First, we calculated the incidence rate of fractures. Second, we constructed logistic regression models to identify factors associated with fracture, including age, sex, race/ethnicity, body mass index, Medicare/Medicaid dual-eligibility, area deprivation index, Charlson comorbidity index, smoking status, osteoporosis, historical fracture, and use of osteoporosis treatment, glucocorticoids, and opioids.

Results
We identified 1,426 adults with prevalent AS. Mean (SD) age was 69.4 years (9.8), 44.3% were female, and 77.3% were non-Hispanic White. Fractures occurred in 197 adults with AS. The overall incidence rate of fractures was 76.7 (95% CI 66.4-88.6) per 1,000 person-years. Older age (OR 2.8, 95% CI 1.39-5.65), historical fracture (OR 5.24, 95% CI 3.44-7.99), and use of >30 mg morphine equivalent (OR 1.86, 95% CI 1.08-3.19) conferred increased odds of fracture.

Conclusions
In this large sample of Medicare beneficiaries with AS, increasing age, historical fracture, and use of opioids had a higher odds of fracture. Men and women were equally likely to have a fracture. Because opioid use was associated with fracture in AS, this high-risk population should be considered for interventions to mitigate risk.