Prevalence and annual incidence of vertebral fractures in patients with ankylosing spondylitis

Objectives To evaluate the prevalence and annual incidence of clinically-manifest vertebral fractures among patients with ankylosing spondylitis (AS). Method: Coordinated by the Ankylosing Spondylitis International Federation, a self-administered general questionnaire which included some questions on gender, age, age at onset of disease, and a history of vertebral fracture was inserted in one issue of the membership journals of the AS patient organizations in Germany and Austria. Results: Among the 1,071 patients responding who all had indicated that the diagnosis of AS had been established or confirmed by a physician, 61 (5.7%) indicated a history of vertebral fracture, 15 of them (1.4%) without an accident. The prevalence of vertebral fractures was 6.2% among male AS patients and 4.6% among females (NS), and 4.8% among HLA-B27+ patients and 9.9% among HLA-B27⁻ patients (p<0.05). Spinal fractures occurred more often among AS patients with peripheral arthritis (7.1%) than among patients with axial involvement only (3.1%, p<0.01). The average delay between disease onset and diagnosis of AS was 10.5 years for patients with a vertebral fracture, compared to 8.7 years for patients without any such event (p<0.05). Among patients with a disease duration ≥42 years, the prevalence of vertebral fractures was 14%. The annual incidence of vertebral fractures which occurred without an accident had a maximum of 0.1% per annum at a disease duration of 20–35 years, whereas the incidence of vertebral fractures caused by an accident increased continuously with increasing disease duration, amounting to 1.3% per annum after a disease duration of 45 years. Conclusion: A considerable proportion of AS patients will experience a vertebral fracture during the course of the disease, in particular if peripheral joints are also involved.