Risk factors for postoperative coronal imbalance after surgical correction of adult spinal deformities: a systematic review with pooled analysis

Objective: The aim of this study was to identify preoperative risk factors for postoperative coronal imbalance (CIB) in patients undergoing surgical correction for adult spinal deformity (ASD). Methods: A systematic search of articles about risk factors for postoperative CIB was conducted on electronic databases (PubMed, EMBASE, and Cochrane Library) according to the PRISMA guidelines. The methodological quality of the included articles was assessed using the Institute of Health Economics Quality Appraisal Checklist for Case Series Studies. Data regarding the patient population (demographics, diagnosis, and follow-up), pre- and postoperative radiographic and clinical data, surgical procedure details, and complications were extracted and summarized. Meta-analyses were performed when possible. Results: Nine studies comprising 838 patients were included. The pooled incidence of postoperative CIB was 26%; preoperative sagittal vertical axis (SVA) and type C imbalance (trunk shifted toward the convexity) were found to be the only primary risk factors for iatrogenic CIB (p < 0.001 and p = 0.012, respectively). Conclusions: Baseline evaluation of a patient's global alignment is of outmost importance when planning surgery for ASD. Type C coronal imbalance (trunk shifted toward the convexity of the main curve) and increased preoperative SVA put the patient at risk of postoperative CIB. Intraoperatively, care should be taken to properly correct the lumbosacral fractional curve.