Femoral and Global Femoral Offset, but not Anteroposterior Offset, to Improve Postoperative Outcomes Following Total Hip Arthroplasty: Considerations Independent of the Contralateral Side

The global femoral offset (the sum of the acetabular and femoral offsets) influences outcomes after total hip arthroplasty (THA). The optimal offset using plain radiographs has been reported, but internal and external rotations of the hip affect the offset value, producing unclear results when the nonsurgical side is not intact. We investigated the relationship between a functional hip score, i.e., the Harris Hip Score (HHS) and its effect on the post-THA anteroposterior and lateral offsets, and we sought to identify the optimal offset value. The cases of 158 patients with hemilateral hip osteoarthritis who underwent THA at a single center were retrospectively analyzed in this cross-sectional study. Three-dimensional pelvic and femoral models generated from computed tomography were used to examine several parameters, and the results revealed a significant binomial correlation among the modified HHS and femoral and global femoral offsets, with maximum values of 21.3 mm and 40 mm/100 cm body height, respectively. Pelvic and femoral parameters were measured and evaluated via alignment with a specific coordinate system. Our findings indicate that preoperative planning using these parameters may improve postoperative hip function, even when the nonoperative side is unsuitable for use as a reference, as in bilateral hip osteoarthritis cases.