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.