Ankylosing spondylitis confers substantially increased risk of clinical spine fractures: a nationwide case-control study

Ankylosing spondylitis (AS) leads to osteopenia/osteoporosis and spine rigidity. We conducted a case-control study and found that AS-affected patients have a 5-fold and 50 % increased risk of clinical spine and all clinical fractures, respectively. Excess risk of both is highest in the first years and warrants an early bone health assessment after diagnosis.

Ankylosing spondylitis (AS) is related to spine rigidity and reduced bone mass, but data on its impact on fracture risk are scarce. We aimed to study the association between AS and clinical fractures using a case-control design.

From the Danish Health Registries, we identified all subjects who sustained a fracture in the year 2000 (cases) and matched up to three controls by year of birth, gender and region. Clinically diagnosed AS was identified using International Classification of Diseases, 8th revision (ICD-8; 71249), and International Classification of Diseases, 10th revision (ICD-10; M45) codes. We also studied the impact of AS duration. Conditional logistic regression was used to estimate crude and adjusted odds ratios (ORs) for non-traumatic fractures (any site, clinical spine and non-vertebral) according to AS status and time since AS diagnosis. Multivariate models were adjusted for fracture history, socio-economic status, previous medical consultations, alcoholism and use of oral glucocorticoids.

We identified 139/124,655 (0.11 %) AS fracture cases, compared to 271/373,962 (0.07 %) AS controls. Unadjusted (age- and gender-matched) odds ratio (OR) were 1.54 [95 % confidence interval (95 %CI) 1.26-1.89] for any fracture, 5.42 [2.50-11.70] for spine and 1.39 [1.12-1.73] for non-vertebral fracture. The risk peaked in the first 2.5 years following AS diagnosis: OR 2.69 [1.84-3.92] for any fracture.

Patients with AS have a 5-fold higher risk of clinical spine fracture and a 35 % increased risk of non-vertebral fracture. This excess risk peaks early, in the first 2.5 years of AS disease. Patients should be assessed for fracture risk early after AS diagnosis.