Effect of hip flexion contracture on the pelvic sagittal tilt in the supine position: A retrospective case-series study.

Abstract

The functional pelvic plane, which adopts the natural pelvic sagittal tilt in the supine position, is a good reference for determining the cup angle in total hip arthroplasty. However, hip flexion contracture may change pelvic tilt postoperatively by the release of contracture. This study investigated the influence of hip flexion contracture on pelvic sagittal tilt in the supine position. This study included 300 patients who underwent primary unilateral total hip arthroplasty. We divided the participants into two groups: with a preoperative hip extension angle of <0° (hip flexion contracture group) and without (non-contracture group). The pelvic sagittal tilt and femoral flexion angle were investigated using computed tomography or pelvic radiographs performed preoperatively and postoperatively. The femoral flexion angle had significantly reduced postoperatively in the hip flexion contracture group but remained unchanged in the non-contracture group. The preoperative and postoperative pelvic sagittal tilt showed no significant differences between the two groups up to 1 year postoperatively. The influence of hip flexion contracture on the pelvic sagittal tilt in the supine position was minimal. The functional pelvic plane in the supine position could be a good reference to ascertain the cup orientation, even in hip flexion contracture cases.