Importance of the spinopelvic factors on the pelvic inclination from standing to sitting before total hip arthroplasty.

PURPOSE: Dislocation after total hip arthroplasty (THA) is a major postoperative complication. Even if the cup is in the safe zone, dislocation caused by implant impingement may occur during postural changes. The aim of the present study was to investigate the spinopelvic factors that influence pelvic inclination changes from standing to sitting in patients with hip diseases who were candidates for THA.

METHODS: 74 patients who underwent primary THA were included according to our criteria. The analysis of the sagittal balance of the spinopelvic complex was performed on standing and sitting lateral radiographs. Pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis angle (LLA), thoracic kyphosis angle (TK), and sagittal vertical axis (SVA) were measured. The differences between the standing and sitting positions regarding the spinal and pelvic parameters were analyzed. Correlations between the variables of the spinopelvic parameters were examined using Spearman's rank correlation coefficient.

RESULTS: The changes in SVA, TK, LLA, SS, PT, and PI from the standing to sitting positions, respectively, were -3.9 ± 48.2 mm, -0.1° ± 6.4°, 21.4° ± 17.7°, 22.2° ± 12.2°, -22.3° ± 13.2°, and 0.4° ± 6.9°. The lumbar lordosis was reduced and pelvic rotation was extended from the standing to the sitting position. The correlation coefficient between the change in the SS and that in the LLA was 0.72 (p < 0.0001). The correlation coefficient between the change in PT and that in the LLA was -0.68 (p < 0.0001).

CONCLUSIONS: The change in pelvic inclination from standing to sitting is strongly related to the mobility of the lumbar spine in patients with hip diseases.