33. Biomechanical analysis of the novel active apex correction technique using a patient specific finite element approach with 6-month follow-up

Abstract

<h3>BACKGROUND CONTEXT</h3> Traditionally, SHILLA and growing rods have been the 2 mainstays for surgical treatment of early onset scoliosis (EOS) patients. Multiple studies have previously highlighted the shortcomings of both techniques; the SHILLA suffer a loss of correction or reappearance of deformity through crank-shafting or adding-on (eg, distal migration) and growing rods require multiple reoperation with additional complications. Newer techniques like the active apex correction (APC) provide an excellent surgical alternate; designed to reduce the prevalence of above complication by avoiding apical fusion amongst other benefits. The current study builds on earlier clinical studies on the APC technique, exploring the clinical of the technique using a finite element (FE) approach. <h3>PURPOSE</h3> The objective is to simulate and explore the effect of apical remodulation using the APC technique over a 6-month follow-up period for 2 patient-specific FE models. <h3>STUDY DESIGN/SETTING</h3> A patient-specific, FE study simulating APC with 6-months follow-up. <h3>METHODS</h3> Two representative scoliotic models were developed to match patient AP and lateral radiographs provided by the surgeon. To simulate the APC technique; the apex was pushed medially followed by compression of the convex side of apex (using 2 screws implanted proximal and distal to the most wedged vertebrae). The rest of construct was then completed to simulate the APC (patient 1 had a dual compression done at primary and secondary curves). The model then simulated the effect of gravity and muscle forces, followed by epiphyseal spinal growth based on the Hueter-Volkmann principle. Relevant clinical output parameters such as primary cobb, AVT, vertebral wedging etc. were recorded for these two models and compared with the clinical data (as available). To ensure clinical relevance, at each step the model inputs and process were checked by a surgeon who regularly performs APC. <h3>RESULTS</h3> Both patient 1 and 2 showed a significant reduction in the Cobb angle (24° and 15°, respectively) for the primary curve following the APC surgery. The AVT was significantly reduced with the surgical correction (∼ 50% in both cases). Additionally, the vertebral wedging in the apical region was significantly reduced due to the APC technique for both patients. Kyphotic angles (T4-T12) were also reduced by 50 % and 40% for patient 1 &2 respectively. Furthermore, at the gravity loading and 6-month spinal growth time points, the output parameters showed a consistent maintenance of the correction achieved by the APC technique (reduction in the Cobb angle, vertebral wedging and translation) for both patients. <h3>CONCLUSIONS</h3> The output parameters from the FE models suggest excellent clinical outcomes; maintenance of coronal correction, reduction in AVT and apical vertebral wedging. While this study is limited in terms of follow-up time as well as sample size, it paves the way for additional research expanding the preliminary results to get a broader biomechanical understanding of the APC. At the same time, the results showcase the enormous potential of this novel technique as a legitimate alternative to incumbent techniques, that can be employed by spine surgeons across the world in an easy, effective and cost-effective manner. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.