Immediate postoperative coronal imbalance in Lenke 5 and Lenke 6 adolescent idiopathic scoliosis: Is it predictable?

PURPOSE: Immediate postoperative coronal imbalance (IPCIB) is a common reason for worse postoperative appearance in adolescent idiopathic scoliosis (AIS) patients and rarely improves on its own at follow-up, thereby greatly influencing the patients' health-related quality of life. However, no studies have been performed to detect the primary risk factors for IPCIB and it remains unclear whether the condition can be predicted preoperatively. The purpose of this study is to detect the primary risk factors for IPCIB in Lenke 5 and Lenke 6 AIS patients and to explore whether IPCIB can be predicted preoperatively.
METHODS: Medical records of Lenke 5 and Lenke 6 AIS patients who underwent correction surgery in our hospital from June 2017 to October 2018 were analyzed. Anteroposterior films were evaluated before and after surgery. Patients were divided into two groups, i.e., occurrence and non-occurrence of IPCIB. The risk factors for IPCIB were analyzed, and an IPCIB index was proposed and verified.
RESULTS: Thirty-seven Lenke 5/Lenke 6 AIS patients with IPCIB and 48 patients without IPCIB were recruited. Univariate analysis showed that there were significant differences between the two groups in the number of unfused vertebrae, preoperative thoracic Cobb angle, preoperative lumbar Cobb angle, preoperative translation of lumbar apex, preoperative coronal balance, preoperative L5 tilt, preoperative bending L5 tilt, postoperative translation of thoracic apex, postoperative lumbar Cobb angle, postoperative translation of lumbar apex, postoperative radiographic shoulder height, and postoperative L5 tilt. Logistic regression analysis showed that the preoperative bending L5 tilt, postoperative translation of the thoracic apex, and postoperative lumbar Cobb angle were the primary risk factors for IPCIB. The IPCIB index was defined as 1.3 * preoperative bending L5 tilt + 1.5 * postoperative translation of thoracic apex - 0.8 * postoperative lumbar Cobb angle. The receiver operating characteristics curve indicated that the occurrence rate of IPCIB was 88% and the non-occurrence rate was 90% when the IPCIB index was greater than 16.
CONCLUSION: The preoperative bending L5 tilt, postoperative translation of the thoracic apex, and the postoperative lumbar Cobb angle were the primary risk factors for IPCIB in Lenke 5 and Lenke 6 AIS patients. The IPCIB index can be used to predict the occurrence of IPCIB with high accuracy. Our results indicate that the thoracic curve should be adequately corrected during surgery; however, moderate correction of the lumbar curve is recommended. These slides can be retrieved under Electronic Supplementary Material.