Vertebral fractures in ankylosing spondylitis are associated with lower bone mineral density in both central and peripheral skeleton

Objective. To study the prevalence and risk factors for vertebral fractures (VF) in ankylosing spondylitis (AS) and the relation between VF, measures of disease activity, and bone mineral density (BMD) in different measurement sites.

Methods. Patients with AS (modified New York criteria) underwent examination, answered questionnaires, and gave blood samples. Lateral spine radiographs were scored for VF (Genant score) and syndesmophyte formation through modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). BMD was measured with dual-energy x-ray absorptiometry in the hip, radius, and lumbar spine in anteroposterior and lateral projections with estimation of volumetric BMD (vBMD).

Results. Two hundred four patients (57% men) with a mean age of 50 ± 13 years and disease duration 15 ± 11 years were included. VF were diagnosed in 24 patients (12%), but were previously noted clinically in only 3 of the 24. Patients with VF were significantly older (p = 0.004), had longer disease duration (p = 0.011), higher Bath Ankylosing Spondylitis Metrology Index (p = 0.011), mSASSS (p = 0.035), and Bath Ankylosing Spondylitis patient global score-2 (BASG-2) (p = 0.032) and were more often smokers (p = 0.032). All women with a VF were postmenopausal. BMD was significantly lower at all measuring sites in the patients with VF. In logistic regression, high BASG-2, low BMD in femoral neck, and low lumbar vBMD were independently associated with presence of VF.

Conclusion. VF in AS are common but are often not diagnosed. VF are associated with advanced age, longstanding disease, impaired back mobility, syndesmophyte formation, and lower BMD in both the central and peripheral skeleton. BMD in the femoral neck, total hip, and estimated vBMD showed the strongest association with VF.