The prevalence of ankylosing spondylitis (AS) is estimated to be 0.8% in southern Chinese. However, the number of patients requiring spinal surgery is much less and in fact in declining trend. The exact reason is not certain but is likely due to the improved medical treatment and other conservative measures. Spinal surgery, if necessary, is usually performed to correct kyphotic deformities or to stabilize spinal fractures and their sequel.
The indications for correction of a fixed kyphotic deformity in AS are relative. AS patients have difficulty looking straight ahead. They have to bend the knees and lean the trunk backwards in order to have a horizontal visual angle (Figure 1) restricting their activities of daily living. Severe kyphotic deformities may also compress the abdominal viscera and limit pulmonary function. As a result, the primary indication for surgical intervention depends on the magnitude of the deformity and the limitation of function.