Postoperative Gravity Line-Hip Axis Offset as a Substantial Risk Factor for Mechanical Failure After Adult Spinal Deformity Correction Surgery.

Background: Mechanical failure (MF) is a serious burden for patients with adult spinal deformity (ASD) who have undergone deformity correction surgery. Surgeons have sought to understand the mechanism and prevent this problematic complication, but this goal remains to be achieved. The gravity line (GL) of the whole body is a noteworthy parameter that represents global sagittal balance, for which normative values for the axial skeleton have been studied.

Objective: To assess postoperative GL-hip axis (GL-HA) offset as a critical risk factor for MF after ASD correction surgery.

Methods: Consecutive patients who underwent initial surgery for ASD at a single academic center were retrospectively included. Demographics, operative details, preoperative and postoperative spinopelvic parameters, global sagittal balance parameters, and Scoliosis Research Society-22 score were evaluated. These variables were analyzed for differences and correlations with MF.

Results: Thirty-five patients without MF and 30 patients with MF were identified in the study. Two groups showed no significant differences in baseline demographics, operative characteristics, preoperative global sagittal balance parameters, or preoperative and postoperative Scoliosis Research Society-22 scores. Significant differences and correlations with MF were observed for postoperative GL-HA offset using a cutoff value of 49.3 mm from logistic regression analysis, with an odds ratio of 11.0 (95% confidence interval: 3.45-35.01, P < .0001).

Conclusion: Postoperative GL-HA offset is a substantial risk factor for MF after ASD surgery. Surgical correction of ASD with a GL-HA offset greater than 5 cm is significantly related to MF. The GL should be located near the HA after ASD surgery.