Hip abductor muscle strength after total hip arthroplasty with short stems

Abstract

Excellent clinical results have been reported for total hip arthroplasty (THA) using a short stem. However, the range of variance in positioning of the stem has been reported to be wide. The authors hypothesized that the short stem position influences the femoral offset (FO) and hip abductor muscle strength (AMS) after surgery. The AMS was evaluated in 64 limbs in 32 patients who underwent unilateral THA using a short stem with a normal contralateral hip. The average time of AMS evaluation was 46.3 months postoperatively. The Harris Hip Score (HHS) was used for clinical evaluation. The ratio of the AMS on the reconstructed side to that on the contralateral side was calculated (strength ratio). The valgus angle (VA) of each stem and FO was measured on an anteroposterior hip radiograph. The FO ratio, as the normalized FO, was calculated. Linear regression analyses were performed to investigate the relationships among the VA, FO ratio and strength ratio. The average HHS improved from 57.7 points preoperatively to 94.6 points postoperatively. The VA negatively correlated with the FO ratio (r = -0.511, P = 0.028). The strength ratio negatively correlated with the VA (r = -0.505, P = 0.032) and positively correlated with the FO ratio (r = 0.479, P = 0.0056). The average postoperative HHS was generally satisfactory after THA using a short stem. A more valgus postoperative position of the short stem leads to reduced FO, which causes decreasing postoperative AMS after THA with a short stem.