Higher risk of incident fracture in patients with ankylosing spondylitis compared to the general population

Background: Ankylosing spondylitis (AS) is characterized by pathologic new bone formation and bone loss. Vertebral fracture (VF) is a known complication of AS, whereas the risk of other major osteoporotic fractures (MOFs) is less studied. Objectives: To estimate incidence rates (IRs) of incident fractures (any, VF and other MOF (humerus, forearm and hip)) in patients with AS compared to controls from general population. Methods: This is a nationwide, register-based and observational cohort study including patients diagnosed with AS (n=11611, 65% men, mean age 48 years) identified in the National patient register (NPR) 2001 through 2015, and age- and sex-matched controls (n=58050) from the Swedish Population Register. The study period started 1 January 2007 or 3 months after the first AS diagnosis, whichever came later, and ended at the first occurrence of each fracture outcome (identified in the NPR), death, emigration or 31 December 2016. Patients and controls with any prior fracture in NPR within a 6-year period before start of the study period were not included. Any fracture (except skull and phalangeal fractures), VF and other MOF were identified in NPR according to pre-specified ICD codes. Each fracture outcome was analysed separately. Poisson regression was used to calculate IRs and incidence rate ratios (IRRs), overall and stratified by sex. Kaplan-Meier curves were plotted. Results: In total 807 (7.0%) of patients with AS and 3201 (5.5%) of matched controls had a history of prior fracture within a 6-year period, and were excluded from further analyses. We noted higher IRs for any fracture, VF and other MOF in AS vs controls, see Figure for Kaplan-Meier curves and Table for IRs and IRRs. In sex-stratified analyses, men with AS (vs. male controls) had a higher relative risk for all fracture outcomes, whereas among women with AS (vs. female controls), a higher relative risk was demonstrated for any fracture and VF. 5-year cumulative incidence for any fracture
Supplement: 1Meeting Abstract: FRI0310