Severe Pelvic Obliquity Affects Femoral Offset in Patients with Total Hip Arthroplasty but Not Leg-Length Inequality

Leg-length inequality is an extensively studied complication of total hip arthroplasty in normal patients. However, few studies have focused on the pelvic obliquity of coronal pelvic malrotation. We hypothesized that pelvic obliquity with a fixed abduction/adduction contracture deformity of the hip may intraoperatively affect the release of soft tissues, ultimately resulting in a leg-length inequality. This study also investigated whether the femoral and vertical offsets of total hip arthroplasty were correlated with pelvic obliquity. This prospective study divided 98 patients into six groups based on the inclination of pelvic obliquity before total hip arthroplasty. Leg-length inequality, variation of pelvic obliquity, offset, and vertical offset were measured after total hip arthroplasty. Leg-length inequality and vertical offset were not significantly different among groups, whereas the variation of pelvic obliquity was significantly higher in type IIC pelvic obliquity than in other groups. Type IC pelvic obliquity had a significantly shorter offset than did the other groups, which may have been an important factor leading to type IC pelvic obliquity. Pelvic obliquity exhibited no significant effect on leg-length inequality in patients with total hip arthroplasty. A shorter offset may be caused by the higher tension of the abductor in the operated hip, which may result in the formation of type IC pelvic obliquity. Releasing the abductor contracture and restoring femoral offset are important for increasing hip stability and maintaining pelvic balance following total hip arthroplasty.