Is Pelvic Fixation a Risk Factor for Pelvic Incidence Change After Surgery for Adult Spinal Deformity? A Retrospective Analysis.

Study Design: Retrospective analysis of prospectively collected data.

Objective: This study will evaluate whether the presence of pelvic fusion can affect this PI modification.

Background: In Adult spinal deformity (ASD), restoring sagittal spinal alignment can positively modify the quality of life in patients post-operatively. Restoring this alignment is based on the measurement of the pelvic incidence (PI) which was postulated to be a constant value specific to each person. However, the literature has recently shown that this pelvic parameter can change after ASD surgery.

Methods: This is a retrospective multicenter study of 290 patients who have undergone ASD surgery between 2012 and 2022. These patients were divided into two groups, group A who received pelvic fusion, and group B who did not. Post-operative PI change was defined by an absolute difference of ≥ 6° between pre- and post-operative values. Furthermore, patients were divided into 3 groups pre-operatively based on their PI: low (<40°), medium (40°-60°), and high (>60°).

Results: Of the patients in group A, 80.0% had a change in PI compared to 12.8% in group B (Odds-Ratio=27.2 [13.8; 53.5], P<.001). Furthermore, this change occurred more frequently in males when compared to females (P=0.02). In addition, a logistic regression model controlling for gender, pre-operative PI groups, the change in lumbar lordosis and sacral slope, and pelvic fixation showed that only the latter predicted the post-operative change in PI with an adjusted odd-ratio of 26.3.

Conclusion: In our cohort, 32.1% of the patients operated for ASD had a post-operative change of PI of ≥ 6° which was well within the reported range in the literature. Moreover, pelvic fusion was found to be the only independent risk factor for PI change with an adjusted OR of 26.3.