Coronal Imbalance in Lenke 5C Adolescent Idiopathic Scoliosis Regarding Selecting the Lowest Instrumented Vertebra: Lower End Vertebra versus Lower End Vertebra +1 in Posterior Fusion

Background Choosing the fusion level for posterior fusion in patients with Lenke 5C adolescent idiopathic scoliosis (AIS) is highly associated with coronal balance. Previous studies indicated that in patients with lowest end vertebra tilt >25°, surgeons could extend distal fusion to avoid coronal imbalance (CIB). This study aimed to assess the risk factors for CIB in Lenke 5C scoliosis and to discuss how to select fusion level. Methods We reviewed 59 patients with Lenke 5C AIS in 1 institution with at least 2 years follow-up from 2010 to 2015. Preoperative and 3-month and 2-year postoperative follow-up radiographs were measured using several specific measurements related to coronal balance. Patients were categorized into an LEV (lower end vertebra) group and an LEV+1 group. Results CIB was found in 6/31 patients in the LEV+1 group at final follow-up and not found in the LEV group at the first or final follow-up. The C7 plumb line shifted to the convex side of the central sacral vertical line in 47/59 patients, including all of the 19 patients with CIB after surgery. Patients who underwent fusion at LEV+1 with >25° LEV tilt also showed poor results regarding CIB. Statistically, coronal balance at the final follow-up was correlated with preoperative bending lumbosacral hemicurve ( P  = 0.002) and all 6 patients with CIB had bending lumbosacral hemicurve >15°. No significant difference was found in Scoliosis Research Society–22 questionnaire scores between the 2 groups at 2-year-follow-up. Conclusions Distal fusion extension at LEV+1 is more likely to result in CIB at the first and final follow-up, especially when the bending lumbosacral hemicurve is >15°. Fusion at LEV+1 should not be chosen when LEV is at L4.