gms | German Medical Science

Objectives: Surgical correction of spinal sagittal malalignment affects spinopelvic function and pelvic tilt. It is not yet known to what extent total hip arthroplasty (THA) affects spinal sagittal balance and the spinopelvic complex. A deeper understanding of the interactions between spinal imbalance and pelvic tilt is needed to address the remaining challenge of THA dislocations. The study aimed to evaluate the hypotheses: Do the spinopelvic parameter change after THA? Is the spinopelvic alignment different in patients with spinal sagittal imbalance?

Methods: A prospective radiological observational study from 09/2019-11/2020 was conducted including 153 patients awaiting unilateral THA. Pre- and postoperative biplanar low dose stereoradiograhpy was obtained in standing position. Patients with contralateral THA or spinal fusion were excluded. Two independent investigators assessed C7-sagittal vertical axis (C7-SVA), pelvic incidence-lumbar lordosis mismatch (PI-LL), cervical lordosis (CL), thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA) pre- and postoperatively. A subgroup analysis of the imbalanced groups of C7-SVA (imbalanced >50mm) and PI-LL mismatch (>10°) on spinopelvic alignment was performed. Paired t-test for pre- and postoperative comparison and Spearman's rank correlation coefficient to determine the interrater reliability of the radiographic measurements was used. Significance level was set to p<0.05.

Results and Conclusion: A significant difference in spinopelvic parameters was detected in the pre- to postoperative comparison (TK, SS, PT, APPT, and PFA; p< 0.000), while TK, PT and PFA decreased and SS and APPT increased. In the subgroup analysis of C7-SVA and PI-LL mismatch the imbalanced groups demonstrated significant differences to the balanced groups regarding LL, PT, TK and APPT. Increased PT and decreased APPT, LL and TK were detected in the imbalanced groups indicating a significant pelvic retroversion and flattened lumbar lordosis. 43.1% (66/153) of the patients revealed a sagittal spinal imbalance regarding C7-SVA ( >50mm) preoperatively.

The results suggest an effect of THA on spinopelvic alignment, with a significant reduction of PT postoperatively. Particularly striking are the significant differences in the spinal imbalanced groups with respect to LL and PT, which may be classified as risk population due to an increased risk of posterior impingement and anterior THA dislocation during standing. The substantial proportion of sagittal imbalanced patients in THA collective illustrates the crucial need for interdisciplinary collaboration between arthroplasty and spine surgeons.