BACKGROUND: Bone mineral density is decreased in patients with ankylosing spondylitis (AS) compared to non-diseased individuals, and the risk of vertebral fracture is increased in AS. The risk of limb fractures in AS, however, has not been well studied.
OBJECTIVES: To determine whether AS patients are at increased risk of fractures of the hip, forearm, or humerus in a population-based study.
METHODS: We conducted a retrospective cohort study in the United Kingdom (UK) using data from the General Practice Research Database (GPRD) from January 1988 through January 2002. The GPRD contains the anonymized electronic medical records from about 4% of the UK population. Participating general practitioners routinely record information about patient demographics, diagnoses, prescriptions, hospitalizations, and referrals. Study patients included men and women, aged 15-74 years at the start of follow-up. We assembled a reference cohort of non-diseased patients frequency matched to AS patients on age and gender. The main study outcome was incident fracture at selected sites commonly affected by osteoporosis (hip, forearm, and humerus). Secondary outcomes included incident fractures of the hip alone and vertebrae. For each outcome, we calculated incidence rates and relative rates along with 95% confidence intervals (CI). We used Poisson regression for adjustment of confounders.
RESULTS: We followed a cohort of 6,707 AS patients (79.7% men) for a median duration of 4.1 years. Median age at diagnosis was 34 years. The reference cohort of 134,960 patients was followed for a median duration of 4.2 years. Major findings appear in the Table. The associations between AS and fracture were not substantially changed in additional analyses stratified by gender, adjusted for age and gender, and restricted to patients who were never prescribed corticosteroids.
CONCLUSION: In this large, population-based study, AS patients were at significantly increased risk of fracture at sites traditionally associated with osteoporosis.
