Femoral anteversion, femoral offset, and abductor lever arm after total hip arthroplasty using a modular femoral neck system

Abstract

We studied the effectiveness of a modular femoral neck system for the adjustment of femoral anteversion, femoral offset, and abductor lever arm during total hip arthroplasty (THA) using computed tomography data, and comparing findings in patients with a modular neck femoral component (116 hips) with those in patients with a cemented femoral component (23 hips). In the modular neck group, we intraoperatively evaluated various impingements using trial necks and heads, and selected the appropriate combination of modular neck and head from two types of straight neck, four types of anteverted/retroverted neck, two types of medialized/ lateralized neck, and two types of varus/valgus neck. In the cement group, femoral anteversion was not changed using undersized stems, and an appropriate modular head was selected. While the 15° retroverted necks effectively corrected femora with a mean anteversion of 40.0° (range 28.8°–53.1°), the 15° anteverted necks were effective for femora with a mean anteversion of 14.2° (range, 3.3°–21.9°). Use of the straight or varus necks resulted in an average abductor lever arm value of more than 40 mm, with a mean anteversion of 26.4°. In patients with preoperative anteversion of more than 30°, postoperative anteversion was significantly smaller in the modular neck group than in the cement group (29.6 ± 4.2° vs. 35.3 ± 3.6°). This modular neck system effectively adjusted femoral anteversion and abductor lever arm in femora with various preoperative anteversion values.