Possibility of Predicting Pelvic Inclination Following Total Hip Arthroplasty Based on the Preoperative State: Sacral Slope and Pelvic Incidence Minus Lumbar Lordosis as Predictive Factors

Following total hip arthroplasty (THA), some patients exhibit anterior or posterior pelvic tilt (PT). This case– control study investigated whether changes to PT following THA can be preoperatively predicted. Methods: 135 patients with hip osteoarthritis who underwent THA were assessed. The parameters measured preoperatively and one year postoperatively were lumbar lordosis (LL) based on plain X-ray and pelvic incidence (PI), PT, and sacral slope (SS), all of which were measured as pelvic morphological angles. Patients were classified into groups (A–E) based on the degree of post-THA PT, and their preoperative conditions were compared. PI minus LL was used to evaluate spinal alignment and pelvic balance. Results: Overall, 33%, 30%, 21%, 13%, and 3% of the hips of patients in Groups A, B, C, D, and E were postoperatively assessed. In Groups A–E, the SS values were 34.6°±8.9°, 37.6°±8.4°, 37.9°±8.9°, 42.6°±9.5°, and 60.0°±11.1°, whereas the PI minus LL values were 2.9°±15.0°, 1.2°±13.6°, 3.6°±17.7°, 12.7°±13.1°, and −1.3°±11.7°, respectively. Conclusions: Following THA, 70% of patients experienced posterior PT. Pre-THA SS ≥45° or PI minus LL ≥15° signified marked postoperative posterior tilt and could predict postoperative PT following THA. These findings are useful for implant placement, as they can predict pelvic inclination.