Current pelvic plane software is not accurate and do not address normal acetabular center axis that has minimum impingement and maximum stability relation with femur in navigated THA A retrospective study of 137 consecutive THA, comparing ACA and APP registration data with postoperative pelvic CT, independently measuring acetabular and cup inclination and version. APP registration points were anterior superior iliac spines and symphysis pubis. Computer identifies preoperative ACA as ‘zero’ after averaging superior, anterior and posterior rim points of registration of acetabulum. Reaming and cup orientation is kept within 4 mm of ACA or within 5 degrees of inclination and anteversion of APP software to avoid impingement.Introduction:
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