Coronal imbalance in adult spinal deformity after corrective surgery: an analysis on the risk factors

English Keywords:Adult spinal deformity  Coronal imbalance  Coronal balance distance  Kaplan-Meier analysis

English Abstract:

  【Abstract】 Objectives: To investigate the risk factors resulting in coronal imbalance(CIB) in adult spinal deformity(ASD) after correction surgery. Methods: A single-center prospective study including 90 ASD patients underwent long segment fusion(≥5 vertebras) surgeries was performed. According to the relationship between preoperative C7 plumb line(C7PL) and scoliosis direction, the patients were subdivided into Group A with consistent spino-pelvis alignment(C7PL located at the convex side) and group B(C7PL at the concave side). CIB was considered if the coronal balance distance(CBD), the distance between C7PL and the midpoint of S1 >30mm. Pearson-correlation and stepwise multiple-regression analysis were used to investigate coronal radiographic parameters related to CBD early postoperatively. A Kaplan-Meier curve was used to analyze the survival time in CIB-free patients during follow-up. Multivariate analysis via a Cox proportional hazards model was used to analyze the risk factors. Results: 20 out of the 90 patients(22.2%) showed CIB preoperatively, and the number increased to 27 at the immediate post-operation, which was 35(38.9%) at the final follow-up, significantly higher than that before operation(P=0.015). In group A, 11 patients showed CIB preoperatively, the number was 22 at the final follow-up, with a significant increase in the incidence of CIB(P=0.019); and in group B, there was no statistical difference in terms of incidence of CIB between preoperation and final follow-up. Comparing to those without pelvic fusion, patients with pelvic fixation had much higher incidence of CIB at the final follow-up(P<0.001). Kaplan-Meier curve demonstrated the survival time of CIB-free patients aged >60 years and with pelvic fixation was significantly shortened. Multivariate Cox risk proportional regression analysis revealed age >60 years, pelvic fixation, and consistent spino-pelvis alignment were the risk factors for CIB surgery. Although early postoperative CBD corelated significantly with L4 tilt, L5 tilt, major curve Cobb, and their corrections(P<0.01), multiple-regression analysis revealed only the preoperative L5 tilt was the independent influencing factor of postoperative CBD(r2=0.295，P<0.001). Conclusions: Elderly ASD patients with consistent spino-pelvis alignment underwent thoracolumbar fusion surgery extending to pelvis may be at the greatest risk for CIB developing during follow-up.