Objective: To study the prevalence of deformities of vertebrae and intervertebral 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- (Hm), and posterior height (Hp) of the vertebrae and intervertebral discs were measured on lateral radiographs of the thoracic (Th5-Th12) 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 > 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 OWD 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.