Hyper-Selective Posterior Fusion in Lenke 5C Adolescent Idiopathic Scoliosis When Can We Stop Below the Upper End Vertebra?

Study Design. A prospective analysis. Objective. To investigate whether the hyper-selective posterior fusion (upper instrumented vertebra [UIV] as the vertebra one level below the upper end vertebra [UEV], lower instrumented vertebra [LIV] as the lower end vertebra [LEV]) was applicable in posterior fusion of Lenke 5C adolescent idiopathic scoliosis (AIS) patients and what could be the indication of hyperselective fusion. Summary of Background Data. The improper UIV selection in selective fusion could lead to progressive thoracic compensatory curve, shoulder imbalance, and even coronal imbalance. However, few studies analyzed the clinical outcome of hyperselective fusion. Methods. A prospective analysis of 80 patients with Lenke 5C AIS who underwent selective fusion was performed. According to the relationship between UEV and UIV, the patients were divided into UEV group (UIV = UEV) and UEV-1 group (UIV = UEV-1). Radiographic parameters and the incidence of postoperative proximal decompensation were compared. The Scoliosis Research Society (SRS)-22 scores were used to evaluate clinical outcomes between two groups. Results. Thirteen patients (27%) in UEV group and six (18.75%) in UEV-1 group showed proximal decompensation during follow-up, and the incidence was equivalent (P = 0.280). Within the UEV-1 group, the patients with proximal decompensation showed similar Risser grade, baseline thoracic Cobb angle, and main Cobb angle (P = 0.611, 0.435, 0.708, respectively). However, the baseline L-T apical vertebral translation (AVT) ratio was significantly larger in patients with proximal decompensation (P = 0.028). Meanwhile, patients with proximal decompensation in UEV group showed significantly smaller preoperative UIV translation and lumbar AVT but similar postoperative UIV tilt. Conclusion. Hyper-selective posterior fusion strategy could be performed in Lenke 5C patients with Risser more than grade 2 and with thoracic compensatory curve over 158. The UIV in patients with small baseline thoracic curve, represented by larger baseline lumbar-thoracic AVT ratio, should be selected as UEV to prevent proximal decompensation.