Fig. 1

Radiograph features of patients with advanced hip lesions in ankylosing spondylitis who underwent primary cementless total hip arthroplasty (a and c for stable disease; b and d for active disease). For A and B, near complete fusion of the sacroiliac joints with erosive changes at the pubic symphysis were observed. Hip involvement is generally bilateral and symmetric, with significant joint space narrowing, reduced density of trabecular bone, cortical thinning and osteophytes