Calculating the hip center of rotation using contralateral pelvic anatomy.

Failure to place an artificial hip in the optimal center of rotation results in poor hip function and costly complications. The aim of this study was to develop robust methodology to estimate hip center of rotation (hCoR) from preoperative computed tomography (CT) scans, using contralateral anatomy, in patients with unilateral diseased hips. Ten patients (five male, five female) with normal pelvic anatomy, and one patient with a unilateral dysplastic acetabulum were recruited from the London Implant Retrieval center image bank. 3D models of each pelvis were generated using commercial software. Two methods for estimation of hCoR were compared. Method 1 used a mirroring technique alone. Method 2 utilized mirroring and automatic alignment. Predicted versus actual hCoR co-ordinates were compared using intraclass correlation coefficients and paired T-tests. Both methods predicted hCoR with excellent agreement to original co-ordinates (>0.9) in all axes. Both techniques allowed prediction of the hCoR within ± 5 mm in all axes. Both techniques provided useful clinical information for planning acetabular reconstruction in patients with unilateral defects. Method 1 was less complex and is suitable for patients with developmental and degenerative pathologies. Method 2 may provide greater accuracy in a discrete group of patients with normal development prior to pathology (e.g., acetabular fractures).