High prevalence of thoracic vertebral deformities and discal wedging in ankylosing spondylitis patients with hyperkyphosis

Objective. To study the prevalence of deformities of vertebrae and inter-vertebral discs in patients with ankylosing spondylitis (AS) in relation to fixed hyperkyphosis of the spine. Methods. Altogether 50 patients (15 women, 35 men) with AS were studied. Hyperkyphosis was measured by the occiput to wall distance (OWD). Anterior (Ha), mid- (Hin), and posterior height (Hpi) of the vertebrae and intervertebral discs were measured on lateral radiographs of the thoracic (Th5-Thl'22) and lumbar spine (L1-L5). Vertebral shapes were analyzed according to McCloskey, et al. Wedging of discs was calculated as Ha/Hp. Hyperkyphosis was defined as OWD greater than or equal to 1 cm. Results. In the thoracic spine, the prevalence of vertebral deformities was higher in patients with hyperkyphosis (n = 38) compared to patients without hyperkyphosis (n = 12) (45% vs 8%; p = 0.01). The prevalence of thoracic vertebral deformities in patients with hyperkyphosis differed little between men and women (39% vs 58%; p > 0.10) and among patients above and below the age of 45 years (50% vs 33%; p > 0.10). Patients with one or more deformed thoracic vertebrae had a higher mean OVID than patients without deformed vertebrae (12 +/- 7 vs 7 +/- 6 cm; p < 0.01). The total sum of deformities of the thoracic vertebrae and discs explained 43% of the variance of the age adjusted OWD (p < 0.001). Deformities of lumbar vertebrae and discs did not contribute to hyperkyphosis. Conclusion. In patients with AS and hyperkyphosis, deformities of the thoracic vertebrae occur frequently and, together with wedging of the thoracic discs, contribute significantly to fixed hyperkyphosis of the spine.