Abstract
The acetabular component is the most troublesome implant. There is more written about acetabular placement than any other anatomical site. The problems are: Maintenance of center of rotation (COR); Coverage of the cup with correct inclination and anteversion; Maintenance of inclination below 50 degrees; Anteversion must be mated to the femur (combined anteversion).
COR is critical for balance of the correct offset and leg length. The inferior-medial metal edge of the cup should lie over the TAL or just proximal to it. No cortical bone of teardrop is palpable.
Coverage: Inclination of the normal bony acetabulum has a mean of 55 degrees (range to 70 degrees) so the posterior-superior edge of the cup may be uncovered in many hips to keep inclination below 50 degrees. 45 degrees is critical for wear and anteinclination. Anteversion of the cup is not independent of the femur (Brown/Callaghan, Hip Society Award paper). Femur anteversion must be known to precisely position the cup. Cup coverage is important here too. The posterior and anterior edges cannot be proud (may need to ream more medial).
