Ankylosing Spondylitis is Associated with an Increased Risk of Vertebral and Non-Vertebral Clinical Fractures: A Population-Based Cohort Study

Objectives To study the associations between ankylosing spondylitis (AS) and clinical vertebral and non-vertebral fractures. Methods Data from a large population-based public health database in Spain (SIDIAP) were used in this parallel cohort study. All participants registered in SIDIAP on 01/01/2006 were screened to identify those with a diagnosis of AS. Five age-, gender-, and general practice surgery-matched controls were selected for each patient with AS. All participants were followed until 31/12/2011, transfer out, or death date. Fractures during this time were classified as vertebral or non-vertebral. Adjustment was made for potential confounders (tobacco smoking, alcohol consumption, body mass index, and use of oral steroids). Results Of 4,920,353 eligible patients in SIDIAP, 6,474 AS patients with matched controls (n = 32,346) were available. A higher proportion of patients with AS vs controls had clinical vertebral (0.86% vs 0.41%) and non-vertebral (3.4% vs 2.7%) fractures. Adjusted Cox regression models showed an increased risk of clinical vertebral (hazard ratio [HR] 1.93, 95% confidence interval [CI] 1.39 to 2.68, p < 0.001) and non-vertebral (HR 1.19, 95% CI 1.02 to 1.39, p = 0.03) fractures among patients with AS. However, the observed increased risks were apparent only in those not on regular non-steroidal anti-inflammatory drugs (NSAIDs). There were no interactions with inflammatory bowel disease, psoriasis, or previous back pain. Conclusions Patients with AS are at increased risk of vertebral and non-vertebral clinical fractures, independently of various risk factors. Regular use of NSAIDs appears to eliminate the excess fracture risk related to AS, but the mechanisms involved are unknown. © 2014 American Society for Bone and Mineral Research