Fig. 1From: Mid-term results of bilateral synchronous total hip arthroplasty for bony ankylosis in patients with ankylosing spondylitisa Delineation of two-step system. Osteotomy perpendicular to the femoral neck 10 mm from the posterior wall of acetabulum (a). Next, wedge osteotomy was performed (b). The bottom edge of wedge osteotomy is 5 mm (c). b Homann hooks were placed in front and rear of the femoral neck, and osteotomy was performed at the junction of the femoral neck and acetabulumBack to article page