抄録
Objective: The aims of this study were first to investigate changes in lower limb alignment after total hip arthroplasty (THA) and second to examine the influence of lower limb alignment on leg length discrepancy (LLD) after THA.
Methods: Forty-three patients (34 women and 9 men) with unilateral hip osteoarthritis who underwent primary THA were included in this study. The mean age at surgery was 64.9 years (range: 4480). For all patients, we obtained antero-posterior radiographs of the pelvis and whole lower limbs in the standing position before and 12 months after THA. On these radiographs, we measured LLD, as well as the femorotibial angle (FTA) and deviation of the mechanical axis at the knee joint (%MA) as parameters of lower limb alignment. We compared the LLD as measured on radiographs of the pelvis to that on radiographs of the whole lower limbs and investigated the influence of lower limb alignment on the difference in LLD between the two types of radiographs.
Results: The affected leg was initially more valgus than the unaffected leg (p＜0.01), but it tended to be varus after THA (p＜0.01). The discrepancy in FTA between affected and unaffected legs was smaller at 12 months postoperatively; however, the affected leg was still more valgus than the unaffected leg (p＜0.01). When the %MA at the knee joint was the same on the affected and unaffected sides, the LLD as measured on radiographs of the pelvis was the same as that on radiographs of the whole lower limbs. As the deviation of the mechanical axis from the center of the knee joint became greater on the affected side, the LLD as measured on radiographs of the whole lower limbs became shorter than that on the radiographs of the pelvis.
Conclusion: Lower limb alignment tended to be varus after THA. When there was a discrepancy in lower limb alignment between the affected and unaffected legs, a difference in LLD was found between radiographs of the pelvis and of the whole lower limbs. Lower limb alignment should therefore be considered when correcting leg length discrepancy in THA.
