The Risk and Consequences of Vertebral Fracture in Patients with Ankylosing Spondylitis: A Population-based Data Linkage Study

Objective. To compare the long-term prevalence, incidence, and outcomes of vertebral fracture (VF) between ankylosing spondylitis (AS) patients and matched controls, including the role of extraarticular manifestations (EAM) and osteoporosis. Methods. This was a statewide observational study using linked health data for 2321 patients with AS and 22,976 controls presenting to hospital from 1980 to 2015. Data were analyzed using incidence rates (per 1000 person-yrs) and ratios (IRR), multivariable Cox proportional hazards regression, and Kaplan-Meier survival curves. Results. Over a median 13.92 ( interquartile range 7.58-21.67) years of follow-up, patients with AS had a greater VF prevalence and greater incidence of developing a new VF compared to controls (9.3% vs 2.5%, 6.8% vs 1.9%, respectively, all P < 0.001). Patients with AS had an increased risk of developing a VF after adjustments for age, sex, and osteoporosis (HR 2.55, 95% CI 2.11-3.09) compared to controls; this risk remained throughout the study period. Patients with AS were 5 years younger at time of first VF (P = 0.008) and had a greater likelihood of a recurrent VF (IRR 4.64; 95% CI 4.54-4.75) compared to respective controls. Mortality overall was comparable between patients with AS and controls after adjustment for age, sex, osteoporosis, and VF status (HR 0.90; 95% CI 0.80-1.01). Conclusion. The significantly increased risk of VF in patients with AS has not altered following the introduction of tumor necrosis factor inhibitor treatment. Although patients with AS experience a first VF at a younger age than controls, this does not lead to an increased risk of death.