Preoperative Leg Length Discrepancy >2 cm in the Supine Decubitus PositionMay Induce Compensatory Pelvic Obliquity in Patients during Total Hip Arthroplasty.

Abstract

The leg length discrepancy (LLD) in the supine decubitus position may influence the inclination angle of the acetabular component during total hip arthroplasty (THA). The relationship among LLD, pelvic obliquity, and inclination angle of the acetabular component has not been well studied. This study aimed to evaluate the relationship between LLD in supine position and changes in the inclination angle of the acetabular components during THA, and the compensatory ability of the pelvis based on LLD and inclination. A total of 135 patients were prospectively classified into three groups according to the preoperative LLD in the supine decubitus position: the cranial type group had a positive LLD value; the fixed type group had LLD=0; and the caudal type group had a negative LLD value. Patients in the cranial type group and caudal type group were divided into four subgroups based on the LLD value (either positive or negative): LLD >3cm subgroup; 2≤ LLD ≤ 3cm subgroup; 1≤ LLD < 2cm subgroup; and LLD <1cm subgroup. The targeted and final inclination of the acetabular component was measured intra- and postoperatively. The results showed a significant difference in the targeted and final inclination angles among the patients in the cranial type and the caudal type groups. In the caudal type group, increased inclination was observed in the patients of LLD >3cm subgroup (mean 3.13°) and 2≤ LLD ≤ 3cm subgroup (mean 5.17°) after THA, respectively. Decreased inclination (mean, 6.16°) was observed in 2≤ LLD ≤ 3cm subgroup in the cranial type group after THA. Our findings revealed that in patients with discrepancy greater than 2 cm, postural pelvic obliquity imposed a remarkable influence on the inclination.