Predictive Role of Shoulder Imbalance and Residual C7PL – CSVL in Coronal Imbalance After Surgery for Severe and Rigid Scoliosis: A Retrospective Analysis

OBJECTIVE: Coronal balance and shoulder balance affect the results of surgical treatments. Numerous studies on these topics in moderate scoliosis have been reported. However, the risk factors and the association between coronal imbalance and shoulder imbalance in complex spinal deformity remain unknown. The purpose of this study is to investigate whether shoulder imbalance as well as other radiographic factors could predict ultimate coronal imbalance in severe and rigid scoliosis. METHODS: A retrospective study was conducted at our hospital between January 2009 and December 2018. Fifty-one patients with severe and rigid thoracic/thoracolumbar scoliosis (main curve Cobb angle > 80° and flexibility < 25%) were recruited. Patients were divided into the Coronal balance (CB) group (C7PL-CSVL ≤ 20 mm) and the Coronal imbalance (CIB) group (C7PL-CSVL > 20 mm). Then, the patients in the CIB group were stratified based on the aggravation of C7PL-CSVL for further subgroup analysis. Potential risk factors for coronal imbalance and decompensation, including shoulder height data and various radiographic parameters, were analyzed between groups and summarized in a quantitative predictive equation. RESULTS: Of all patients, 43.1% (22/51) showed coronal imbalance at the last follow-up. Univariate analysis showed that the following parameters were significantly greater in CIB group: shoulder height data including immediately postoperative radiographic shoulder height (RSH, p = 0.001), postoperative clavicle angle (CA, p = 0.000), and postoperative C7PL-CSVL (p = 0.000). Logistic regression identified that immediately postoperative CA [odds ratio (OR) = 6.837, p = 0.008] and C7PL-CSVL (OR = 1.071, p = 0.010) were the independent risk factors for ultimate coronal imbalance. The predictive equation was Risk Index = -5.277 + 1.922 × postoperative CA + 0.068 × postoperative C7PL-CSVL, with positive and negative predictive values of 86.7% and 85.7%, respectively. CONCLUSIONS: The prevalence of coronal imbalance at the last follow-up remained high in severe and rigid scoliosis. Postoperative shoulder imbalance and residual trunk shift could be used as predictors for ultimate coronal imbalance. The aggravation of coronal imbalance might represent a possible compensatory response to shoulder imbalance, as suggested by the observed adverse trends. However, this interpretation should be considered hypothetical, since a direct causal relationship could not be verified yet. Surgeons should pay attention to restore an appropriate relationship between curves in surgical planning for better results.