Fig. 1From: The accuracy of acetabular cup placement in primary total hip arthroplasty using an image-free navigation systemImage-free navigation system in this study. Registration of the bilateral anterior superior iliac spines (a, b). Registration of the acetabular fossa, the acetabular cavity, and the anterior rim point (c-e). Intraoperative measurment of the cup insertion angle (e)Back to article page