High variability in pelvic orientation in the lateral decubitus position negatively affects acetabular component placement

Purpose: Determine factors that impart increased risk of acetabular component malposition in the lateral decubitus position. Methods: A retrospective review of 813 X-rays from posterior THA procedures at a single institution. Pelvic tilt and rotation were measured on preoperative standing AP-pelvis and intraoperative cross-table x-rays. Proper intraoperative pelvic orientation (PPO) was defined as vertical tilt and axial rotation within ± 15° of the preoperative standing pelvis orientation. Acetabular abduction was measured on standing postoperative x-rays with Goal abduction (GA) of 30–50°. Results: PPO was obtained in 284/413 cases (69 %). Patient sex, weight, BMI, and operative laterality were not significantly associated with PPO. Patients with PPO were shorter (1.68m vs 1.72m, p < 0.01). PPO occurred in 168/221 patients (76 %) with the Capello or Wixson hip positioner, compared to 116/192 (60 %) with the De Mayo positioner (p < 0.01). GA was obtained in 249/284 (88 %) of patients with PPO, as compared to 103/129 (80 %) patients without PPO. Conclusion: The risk of pelvic malpositioning significantly increases with the use of certain hip positioning systems, and taller patients. Acetabular component abduction is negatively affected by an improperly positioned pelvis.