Thoracic compensation after pediatric lumbar spinal fusion: adaptations in the sagittal plane

PURPOSE: Sagittal plane changes after isolated lumbar fusion for pediatric idiopathic scoliosis are under-reported in current literature. Understanding how the thoracic spine compensates after this surgery will help optimize surgical technique. This study aims to determine the thoracic compensation and the change in other sagittal plane variables after lumbar fusion. METHODS: This was an IRB approved retrospective study that included patients if they were between 11 and 18 with idiopathic scoliosis with lumbar major patterns that underwent isolated thoracolumbar/lumbar fusion. Spinal radiographs were reviewed at 3 timepoints: pre-operative, 6 weeks post-operative, and long-term (at or greater than 2 years) post-operative to assess sagittal plane parameters. Linear mixed effect model, regression analysis with Pearson's correlation coefficient, and Fisher exact analyses were used to identify differences across these timepoints for quantitative and categorical variables. RESULTS: 45 patients met inclusion criteria. The median age was 15 (range 11-18) and average follow up was 4.04 years. There were 38 female and 7 male patients. The thoracic spine became more kyphotic after surgery (M diff. pre-op to 2 years T5-T10 = 4.7°, p < 0.05). Additionally, 22% developed radiographic proximal junctional kyphosis at 2 years. The lumbar segments became increasingly more lordotic after surgery (M diff. L1-S1 pre-op to 2 years = - 5.6°, p < 0.05). Lower pre-operative sagittal thoracic curvature was significantly associated with increased post-operative thoracic kyphosis (T5-T10 pre- to 2-year post-op r = - 0.31, p = 0.04). Lower pre-operative sagittal lumbar curvature was also significantly associated with increased post-operative lumbar lordosis kyphosis (L1-S1 pre- to 2-year post-op r = - 0.4, p = 0.01). Age, BMI, and number of fused segments did not correlate significantly with thoracic or lumbar change post-operatively. CONCLUSIONS: Isolated lumbar fusion for pediatric idiopathic scoliosis is associated with increasing thoracic kyphosis. Additionally, the lumbar spine became more lordotic after surgery. These effects became pronounced in patients with low sagittal plane pre-operative curvature. Anticipating these adaptations will help guide surgical planning to optimize the sagittal plane.