A novel classification of coronal malalignment in degenerative lumbar scoliosis for predicting postoperative coronal imbalance: a multicenter cohort study

OBJECTIVE The aim of this study was to investigate the major risk factors of postoperative coronal imbalance (CIB) in patients with degenerative lumbar scoliosis (DLS) and to establish a novel predictive classification system for postoperative CIB. METHODS A multi-institutional, retrospective cohort study was conducted and included 269 patients with DLS who underwent posterior long-segment instrumentation and fusion. Patients were divided into two groups: those with postoperative CIB and those with postoperative coronal balance. Clinical and radiographic data were compared between the two groups. Coronal measurements included the orientation of the C7 plumb line (C7PL), coronal balance distance (CBD), major curve, lumbosacral fractional curve, L4 coronal tilt, L5 coronal tilt, upper instrumented vertebra coronal tilt, and apical vertebral translation. A novel classification was developed based on the factors identified in the multivariate logistic regression analysis. RESULTS A total of 104 patients (38.7%) developed postoperative CIB. C7PL orientation and L4 coronal tilt were identified as the most significant predictors of postoperative CIB. Accordingly, patients were classified into 4 types based on their coronal malalignment: type 1a, concave-side C7PL, L4 coronal tilt < 17.5°; n = 84; type 1b, concave-side C7PL, L4 coronal tilt > 17.5°; n = 44; type 2a, convex-side C7PL, L4 coronal tilt < 17.5°; n = 70; and type 2b, convex-side C7PL, L4 coronal tilt > 17.5°; n = 71. Type 2b had the highest incidence of postoperative CIB (73.2%), while type 1a exhibited the lowest risk (8.3%). A distinct distribution of CIB patterns was observed in type 1 and type 2. The receiver operating characteristic curve analysis indicated that the new classification had strong predictive performance for postoperative CIB (area under the curve 0.788, 95% CI 0.733–0.843). CONCLUSIONS The authors propose a novel coronal classification system that improves preoperative risk stratification for postoperative CIB, which may assist in surgical decision-making regarding coronal realignment in DLS surgery.