The effect of preoperative lateral flexibility of the lumbar spine on perceived leg length discrepancy after total hip arthroplasty.

BACKGROUND Leg length discrepancy (LLD) after total hip arthroplasty (THA) is a significant factor of patient dissatisfaction. Patients with dissociation between preoperative radiographic LLD and perceived LLD sometimes feel LLD postoperatively even if bilateral leg lengths are equal. There is no publication describing how to decide the amount of leg lengthening in such cases. PURPOSE By examining the influence of preoperative lumbar lateral flexibility on postoperative perceived LLD, this study aims at creating a guideline for the optimal planning of leg lengthening in THA. METHODS In 59 cases undergoing primary unilateral THA, radiographic LLD, perceived LLD, pelvic tilting and lumbar lateral flexibility were measured preoperatively. The amount of leg lengthening and the sequential change of the perceived LLD were measured postoperatively. RESULTS Twelve cases (20%) felt the perceived LLD at two years after surgery. All these cases felt the operative side longer than the non-operative side. In 32 cases with preoperative pelvic inclination to the affected side, postoperative perceived LLD was significantly greater if lumbar spine was rigid. In eight cases with pelvic tilting and rigid lumber spine, the amount of leg lengthening that exceeded preoperative perceived LLD affected the postoperative perceived LLD. CONCLUSIONS In cases with preoperative pelvic inclination downward to the affected side and with rigid lumbar spine, amount of leg lengthening should not be excessively greater than preoperative perceived LLD. In other cases, lengthening the leg to the same length as the contralateral side rarely results in postoperative perceived LLD.