A high body mass index tilts the pelvis caudally in the lateral decubitus position for total hip arthroplasty

Abstract

Background: Accurate cup placement is essential for obtaining excellent outcomes in total hip arthroplasty (THA). We evaluated the pelvic lateral tilt of the patient (which affects the incline of the acetabular cup in THA) and investigated the factors affecting it. Methods: We reviewed the medical records of THA procedures performed at our hospital between October 2015 and January 2021 for which an anteroposterior pelvic radiograph was always taken preoperatively once the patient was placed in the lateral decubitus position. These radiographs were used to measure the lateral pelvic tilt in each case. We analysed whether patient factors (sex, body mass index [BMI], range of motion of abduction or adduction in both hips, surgical history of both hips, and lumbar Cobb angle) influenced the tilt. Results: We reviewed 363 cases (341 primary, 22 revision). The mean pelvic lateral tilt was 4.1°, and the operated hip was located on the caudal side compared to the unoperated hip. Statistical analyses revealed that the patient BMI and surgical history of the operated and unoperated hips significantly influenced tilt. Conclusions: The pelvis in the lateral decubitus position leaned 4.1° to the caudal side, most commonly due to a high BMI. Surgeons should consider this when performing acetabular cup implantation in THA.