Prevalence of vertebral fractures by semiautomated morphometry in patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease mainly affecting the axial skeleton and characterized by ossification of the spinal disc, joints, and ligaments leading to progressive ankylosis. Vertebral osteoporosis is a recognized feature of AS. Studies have confirmed a moderate to high prevalence of vertebral fractures with extremely varying ranges in patients with AS. Our objective was to estimate the prevalence of vertebral fractures in a representative Spanish population of patients with AS using a validated semiquantitative method, MorphoXpress(®).

Patients were randomly selected from the 10 initial participating centers of the Spanish National Registry of Spondyloarthropathies (REGISPONSER) by consecutive sampling. All patients fulfilled the New York modified criteria for AS and had a baseline thoracolumbar radiograph. A prevalent vertebral fracture was defined according to the Genant classification criteria.

The estimated prevalence of vertebral fractures was 32.4% (95% CI 25.5%-39.3%). The majority of fractures were localized in the thoracic segment (n = 100; 82.%) and were mild (n = 79; 64.8%). In logistic regression analysis, age (odds ratio per year 1.05, 95% CI 1.03-1.08, p < 0.001), disease duration (OR per year 1.03, 95% CI 1.01-1.06, p = 0.011), Bath Ankylosing Spondylitis Functional Index score (OR per score 1.16, 95% CI 1.03-1.30, p = 0.015), Bath Ankylosing Spondylitis Radiographic Index-TS (OR per score 1.25, 95% CI 1.12-1.39, p < 0.001), and wall-occiput distance (OR per cm 1.15, 95% CI 1.08-1.23, p < 0.001) were all associated with prevalent fracture.

Semiquantitative methods are needed to improve the diagnosis of vertebral fractures in AS in order to start early treatment and to avoid complications arising from osteoporosis.