Selective Versus Nonselective Fusion for Idiopathic Scoliosis Does Lumbosacral Takeoff Angle Change?

Study Design. Retrospective review of a prospective, multicentered database. Objective. To determine the relationship between preoperative lumbosacral takeoff angle (LSTOA) and postoperative thoracolumbar/lumbar Cobb angle (TL/L Cobb angle) in patients undergoing selective thoracic fusions. Summary of Background Data. Selective fusion of the thoracic curve can improve the lumbar curve inpatients with idiopathic thoracic scoliosis and a compensatory lumbar curve. Predicting improvement is controversial and determining whether to perform a selective fusion or nonselective fusion can be difficult. Methods. Patients had undergone either nonselective or selective spinal fusion for adolescent or juvenile idiopathic scoliosis (Lenke 1B/3B/1C/3C). Outcome measures were: coronal and sagittal thoracic Cobb angle, TL/L Cobb angles, lumbar apical vertebral translation, LSTOA and coronal decompensation. Analyses compared relationships between preoperative and postoperative radiographic measures. Results. Positive, significant correlations were found between preoperative LSTOA and preoperative TL/L Cobb angle in the nonselective (r - 0.7; P < 0.001) and selective (r - 0.5; P < 0.001) fusion groups. Mean two-year postoperative coronal TL/L Cobb angles were significantly improved in nonselective and selective fusion groups (32 degrees and 20 degrees, respectively, P < 0.001). In the nonselective fusion group, LSTOA significantly decreased by 11 degrees (P < 0.001), and in the selective group, the LSTOA had a modest but significant decrease of 2 degrees (P < 0.001). The nonselective fusion also resulted in more lordosis between T10 and L2 (7.5 degrees of lordosis) than the selective approach (2.7 degrees kyphosis, P < 0.001). For both groups, upper thoracic kyphosis increased after surgery (P < 0.001, P < 0.001). For nonselective fusions, regression modeling predicted TL/L Cobb angle at two-year follow-up based on preoperative TL/L Cobb angle and preoperative LSTOA (r(2) = 0.4, P < 0.001). Conclusion. Collectively, these data demonstrate the preoperative TL/L Cobb angle and LSTOA can be useful predictors of postoperative TL/L Cobb angle after a selective instrumented fusion. Analyses of distal fixation levels demonstrated that to appreciably change the LSTOA using a posterior instrumented fusion, the distal level of fixation must be beyond the lumbar apex.