Patient preoperative positioning for THA affects postoperative acetabular cup angle and leg length discrepancy: a prospective case series

Proper orientation of the acetabular cup in total hip arthroplasty (THA) is essential to reduce dislocation risk, improve range of motion, and enhance implant longevity. Misalignment can lead to complications such as impingement, wear, and aseptic loosening. Patient positioning on the operating table is a critical yet often overlooked factor influencing pelvic tilt and cup placement accuracy during THA. This study aimed to evaluate the impact of preoperative patient positioning on acetabular component placement and explore whether surgeon experience affects cup placement precision. In this prospective case series, 135 patients undergoing non-navigated THA in the supine position at a single tertiary center were included. Preoperative photographs captured pelvic inclination, which was compared to postoperative cup orientation measured on radiographs. Patients were divided into three groups based on surgeon experience (< 5 years, 5-15 years, > 15 years). Statistical analyses assessed relationships among patient positioning, cup orientation, leg length discrepancy, and surgeon experience. Greater pelvic inclination measured before sterile draping was significantly associated with a smaller acetabular cup angle (Pearson's R = -0.72, p < 0.001). Surgeons with > 15 years of experience demonstrated less variability in cup orientation and leg length discrepancy than those with fewer years of experience (p < 0.001). Despite variations in pelvic positioning, the overall postoperative cup angle was consistent across groups. Preoperative patient positioning significantly impacts acetabular cup orientation, with more experienced surgeons better able to compensate for these deviations. Positioning protocols and surgeon training on pelvic orientation may enhance THA outcomes, particularly for early-career surgeons.