Effect of Pelvic Obliquity on the Orientation of the Acetabular Component in Total Hip Arthroplasty

In infrapelvic obliquity, coronal pelvic malrotation entails a change in the spatial location of the bony acetabulum. In the present study, 77 patients presented with infrapelvic obliquity with types 1 and 2 hip pathologies in which the pelvis is lower and higher, respectively, on the short-leg side. The 2 types were classified into 3 subtypes (A, B, and C) according to the severity of the pelvic obliquity (0 degrees-3 degrees, 3 degrees-6 degrees, and >6 degrees). Angles of inclination of pelvic obliquity postoperatively, anteversions, and inclinations (abduction angle) for acetabular components were measured after total hip arthroplasty. Increased inclination (mean, 8.79 degrees) was observed in type 1 C, where the angle of inclination to pelvic obliquity postoperatively was minimally corrected. This increase may lead to cup instability. Rebalancing the pelvis in these cases with preoperative skeletal traction and/or sufficient release of hip contractures may be necessary. A correction of the mean inclination of the cup by 8.79 degrees is required.