Computational and experimental investigation of the biomechanical effects of implants on spinal segment function

Spinal deformities often require surgical intervention with implants to restore alignment and stability. Due to the complexity of these procedures and the biomechanical challenges that follow, proximal junctional failure (PJF) is common and it includes proximal junctional kyphosis (PJK) and fractures. Despite extensive research examining risk factors and increasing utilization of intraoperative prophylaxis techniques, studies demonstrate a high incidence of PJK with 31.3% being revised within two years. Our goal is to leverage recent advancements in the finite cell method (FCM), finite element analysis (FEA), and the Phase-Field Method (PFM) to evaluate the biomechanical behavior of spinal deformities treated with implants, validated through experimental testing. We will create detailed 3D models of individual vertebrae, functional spine units (FSUs), spine segments, and implant components such as rods and screws, using data from CT and micro-CT scans. Macro-FEA will be applied to analyze overall biomechanical responses, while FCM will provide high-resolution insights at the lamellae level, with a focus on implant-lamellae interactions. The macro- and micro-scales will be interconnected by exchanging data between FEA and FCM. The inhomogeneous and anisotropic material properties of the vertebrae, calculated via numerical homogenization of the micro-CT model, will be integrated into the macro FEA for enhanced structural analysis of vertebrae and FSUs. A novel approach is proposed to link macro- and micro-scale analyses for predicting potential vertebral damage. On the macroscopic scale, a FE model incorporating homogenized material properties will be used to analyze the FSU and individual vertebrae, identifying regions prone to damage based on principal strain criteria. These regions will be further examined using FCM applied to micro-CT scans, and the PFM material model on the macro scale will be calibrated using FCM simulations. This integrated micro-macro approach will allow for a thorough evaluation of potential implant failure and the onset of adjacent segment failure. The computational results will be validated through both experimental testing and clinical observations, ensuring accurate simulation of real-world conditions. This comprehensive method provides a solid framework for optimizing patient-specific pre-surgical planning and surgical techniques, ultimately leading to better outcomes in the treatment of spinal deformities.

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