Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results

Introduction: Restoring a degree of kyphosis consistent with good sagittal alignment of the spine is a key concern when performing surgery to correct adolescent idiopathic scoliosis (AIS). The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was thoracic kyphosis at last follow-up. Hypothesis: The use of pre-bent patient-specific rods has a favourable effect on thoracic kyphosis at last follow-up. Material and methods: A total of 37 patients with AIS, including 17 with hypokyphosis, managed with patient-specific rods were included in a prospective study. The rod contouring angles were based on predefined pelvic incidence criteria (25 degrees to 40 degrees for the rod on the convex side and the same value plus 10 for the rod on the concave side). Thoracic kyphosis was assessed before surgery and at last follow-up, after 12-36 months (mean, 19 months). Student's t test was applied to compare means. Multivariate linear regression analysis was performed. Results: At last follow-up, the mean increase in kyphosis was 14 and was comparable to the planned increase (mean difference = 0, p = 0.85). Factors associated with kyphosis at last follow-up were the concave rod contouring angle and the pre-operative kyphotic angle of the thoracic segment to be instrumented (p < 0.05). Mean differences between kyphosis of the instrumented thoracic segment at last follow-up and target kyphosis were -5 degrees in the subgroup with hypokyphosis (< 20 degrees) before surgery and +4 degrees in the subgroup with normal kyphosis before surgery. Conclusion: With patient-specific rods, kyphosis at last follow-up was close to the target value. Predictors of kyphosis at last follow-up were the concave rod contouring angle and pre-operative kyphotic angle of the thoracic segment to be instrumented. Over-contouring of the concave rod seems necessary in patients with preoperative hypokyphosis but not in patients with normal kyphosis. (C) 2019 Elsevier Masson SAS. All rights reserved.