Prevalence of vertebral compression fractures due to osteoporosis in ankylosing spondylitis.

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Abstract
OBJECTIVE--To determine the prevalence of vertebral compression fractures due to osteoporosis in patients with ankylosing spondylitis. DESIGN--Prospective study of 111 consecutive patients; patients with vertebral compression fractures were entered into a case-control study. SETTING--Outpatient clinic at the centre for rheumatic diseases, Glasgow. PATIENTS--111 Consecutive patients with ankylosing spondylitis. Patients with compression fractures were matched for age and sex with two controls selected from the rest of the group. Patients with biconcave vertebral fractures were also studied. MAIN OUTCOME MEASURES--Assessments of spinal deformity and mobility and analysis of lateral radiographs of spines for presence of syndesmophytes. RESULTS--Fifteen patients with compression fractures and five with biconcave fractures were studied. Compared with the controls the patients with compression fractures had increased formation of syndesmophytes in the lumbar spine, whereas those with biconcave fractures had increased formation throughout the spine. Patients with compression fractures also had a greater degree of spinal deformity (distance from wall to tragus 24.5 cm v 12.7 cm in controls), less spinal mobility (20 v 45.6 degrees of flexion), and reduced chest expansion (2 cm v 3cm). CONCLUSION--Vertebral compression fractures due to osteoporosis are a common but frequently unrecognised complication of ankylosing spondylitis and may contribute to the pathogenesis of spinal deformity and back pain.