Thoracic Kyphosis Correction Using Pre-Bent Patient-Specific Rods in Adolescent Idiopathic Scoliosis: A Retrospective Analysis

Introduction: Adolescent idiopathic scoliosis (AIS) is a three-dimensional congenital deformity of the spine. Current surgical treatment involves a multi-segmental posterior pedicle screw instrumentation and spinal fusion. Most reports focus on the surgical results in the coronal plane, but insufficient sagittal correction may lead to malalignment and accelerated distal segment degeneration. Currently, most surgeons contour rods based on experience during surgery without first determining the desired amount of thoracic kyphosis (TK) or measuring the angle created by the rod. In this study, we aim to determine if pre-bent patient-specific rods provide favorable sagittal alignment in AIS patients using normal reference thoracic kyphosis as our primary criteria. Objectives The main objective of this study was to assess whether the use of pre-bent patient-specific rods in AIS correction leads to improved sagittal alignment by achieving thoracic kyphosis angles that closely match surgically planned values. We sought to evaluate the degree of alignment across different subgroups classified by initial thoracic kyphosis and compare outcomes with normal reference kyphosis. Methods: The study included 67 total patients. Normal thoracic kyphosis reference range was established as between 20° and 40°. Patients were then separated into different subgroups based on their initial visit thoracic kyphosis compared to the referenced range, which included hypokyphosis, normal kyphosis, and hyperkyphosis. Thoracic kyphosis was assessed at three separate time points via plain radiography: initial visit, pre-operative, and most recent follow-up. Surgically planned target kyphosis was determined prior to surgery and used to correct patients to the reference kyphosis range. Paired T-tests were used to analyze thoracic kyphosis between the different subgroups. Results: Mean length to last follow-up was found to be 12.8 months. At the last follow-up, the mean increase in thoracic kyphosis was 13° for the group at large. The mean difference between kyphosis at last follow-up and target kyphosis in the subgroups was as follows: hypokyphosis was -4°, normal kyphosis was 0°, and hyperkyphosis group was +6°. Significant changes were found when comparing all subgroups’ preoperative thoracic kyphosis angles with their surgical plan, and no significant differences were found when comparing their postoperative thoracic kyphosis angle with their surgical plan. Conclusion: Prefabricated patient-specific rods achieved thoracic kyphosis angles close to surgically planned values, resulting in favorable sagittal plane alignment. The findings support the use of patient-specific rods to improve sagittal alignment and reduce the risk of malalignment and distal segment degeneration. Next steps for the study include following the cohort of patients over a longer period to assess the degree of degenerative conditions that develop in each subgroup and conducting a comparative analysis with traditional rods in all three anatomical planes.