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

Abstract

Purpose: The functional pelvic plane (FPP), which adopts the natural pelvic sagittal tilt in the supine position, is a good reference for determining the cup angle in total hip arthroplasty (THA). However, hip flexion contracture may change pelvic tilt post-operatively by the release of contracture. This study investigated the influence of hip flexion contracture on pelvic sagittal tilt in the supine position. Methods: This study included 300 patients who underwent primary unilateral THA. We divided the participants into two groups: with preoperative hip extension angle <0° (hip flexion contracture group) and without (non-contracture group). The pelvic sagittal tilt and femoral flexion angle were investigated using computed tomography (CT) or pelvic radiographs performed preoperatively and postoperatively. Results: 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. Conclusion: The influence of hip flexion contracture on the pelvic sagittal tilt in the supine position was minimal. The FPP in the supine position could be a good reference to ascertain the cup orientation, even in hip flexion contracture cases.