Multivariate analysis of factors associated with kyphosis maintenance in adolescent idiopathic scoliosis.

Study Design: Multicenter retrospective cohort study of 269 patients.
Objective: The purpose of this study is to evaluate the surgical and radiographical factors in adolescent idiopathic scoliosis (AIS) surgery that significantly affect kyphosis maintenance.
Summary of Background Data: Decreased kyphosis in the thoracic spine is a component of the 3-dimensional deformity in AIS. Suboptimal sagittal alignment after spinal fusion has been identified as a possible cause of lumbar and cervical spinal degeneration and junctional malalignment. Segmental spinal instrumentation continues to evolve, and although excellent coronal plane correction is readily achieved, sagittal plane thoracic hypokyphosis may be seen postoperatively.
Methods: A retrospective analysis of prospectively collected data from a multicenter AIS database was performed to evaluate factors associated with kyphosis maintenance. A total of 526 patients were enrolled in the database and had a mean thoracic kyphosis (T5-T12) of 22°. In total, 269 patients were identified who had kyphosis of less than 22° and thus comprised the group to be included in this analysis. A complete radiographical series was obtained for each patient preoperatively, immediately postoperatively, and at 2 years postoperatively. All operative data, including the number of levels fused and implant type and density, were also recorded. Multivariate and regression analysis were performed.
Results: Eight variables were found to be significantly correlated with kyphosis maintenance at 2 years postoperatively. Anterior approach (r = 0.37, P < 0.001), increased thoracic coronal curve (r = 0.20, P = 0.001), and a greater percentage of hooks in the construct (r = 0.18, P = 0.034) were associated with increased kyphosis at follow-up. A greater number of levels fused (r = -0.33, P < 0.001), preoperative kyphosis (r = -0.39, P < 0.001), percentage of screws in the construct (r = -0.18, P = 0.03), using standard stainless steel rods (r = -0.47, P = 0.011), and percent decrease in thoracic curve (r = -0.23, P < 0.001) all were correlated with hypokyphosis at follow-up.
Conclusion: Our multivariate analysis demonstrates that in patients with AIS who have thoracic hypokyphosis as part of their deformity, certain factors must be taken into account in the preoperative planning to prevent hypokyphosis after surgical correction.