Spinopelvic Motion Evaluation in Patients Undergoing Total Hip Arthroplasty and Patient-Specific Target for Acetabular Cup Placement.

Background/Objectives: Instability is a major reason for revision after total hip arthroplasty (THA), and acetabular cup placement in the "traditional" safe zone does not protect against dislocations. Spinopelvic mobility may play a role in impingement and dislocation after THA. Personalized acetabular cup placement that incorporates spinopelvic mobility is currently lacking in the literature. Methods: The spinopelvic motion of 116 patients was evaluated during preoperative planning. All patients underwent radiological assessments with an anteroposterior pelvis radiograph in the standing and supine positions and a lateral view of the lumbar spine and pelvis in the standing and sitting positions. The pelvic incidence, pelvic tilt, sacral slope, standing anterior pelvic plane tilt, sitting anterior pelvic plane tilt, and lumbar lordosis angle were measured, and the degree of pelvic motion from standing to sitting was calculated. The development of the patient-specific target for the acetabular cup was based on the mean mobility of the whole group and the specific posture of each patient. Results: The average pelvic incidence was 51.0 ± 13.1 degrees, the sacral slope was 35.0 ± 10.3 degrees, the pelvic tilt was 16.0 ± 13.3 degrees, the standing anterior pelvic plane tilt was 3.4 ± 12 degrees backward, and the degree of lumbar lordosis was 39.5 ± 11.3 degrees. The mean spinopelvic mobility was 27.3 ± 13.4 degrees. The measurements had good to excellent interobserver and intraobserver reliability. On the basis of these measurements, we developed a novel algorithm for a patient-specific target for acetabular cup placement. Conclusions: the evaluation of spinopelvic mobility has good to excellent interobserver and intraobserver reliability and can be used for personalized acetabular cup placement.