Intraoperative pelvic rotation in total hip arthroplasty with lateral direct anterior approach

Abstract The position of the acetabular cup is important for the outcome of total hip arthroplasty (THA). In THA with a lateral direct anterior approach (LDAA), the pelvis can easily move back and forth on the operating table during surgery. Intraoperative assessment of pelvic rotation is an important component for successful positioning and placement of the acetabular cup in LDAA-THA. We prospectively studied 30 cases of primary THA with LDAA. We used a specially designed mechanical brace and smartphone to measure pelvic motion in the horizontal and coronal planes to improve the accuracy of acetabular cup placement. The results showed that axial rotation of the pelvis occurred in all cases, with a rotation angle of 9.1°±1.0° (range 7.4°-10.9°). The pelvis also tilted upward or downward simultaneously, but the tilt angle was relatively small and not clinically significant. There was no statistically significant correlation between pelvic rotation and patients’ height, weight, or body mass index (BMI). The study found that the pelvis was mainly tilted backward during surgery, with an average backward tilt of 9° in the horizontal plane. Pelvic motion primarily occurred when the Hohmann retractor was used to expose the acetabulum.