Biomechanical study of a novel external fixation frame controlling postoperative loss of reduction in thoracolumbar fractures: Finite element analysis

Objective This study aims to investigate the biomechanical characteristics of percutaneous pedicle screw fixation combined with a novel external fixation device (Micro-Adjustable External Fixation - MAEF) for minimally invasive spinal fracture treatment using finite element analysis, providing theoretical support for clinical application. Methods We simulated an L1 vertebral fracture and constructed two finite element models: CASE 1: Micro-Adjustable External Fixation (MAEF), CASE 2: Percutaneous Short-Segment Intermediate Screw Fixation (PSISF). Under load control, we recorded the percentage change in ROM values before and after fixation for both models, along with maximum stress values at the fixation system, fractured vertebra (L1), T12 inferior endplate, and L2 superior endplate. Results Under all loading conditions, the ROM of the MAEF model was normalized to the ROM of the intact T11–L3 model, ranging from 8.4% to 15.5%. The ROM of the PSISF model was normalized to the intact T12–L2 model, ranging from 48.0% to 70.9%. Compared with the PSISF model, the MAEF model exhibited lower maximum stress values in the fixation system, fractured vertebra (L1), inferior endplate of T12, and superior endplate of L2. Furthermore, the maximum stress values for the fixation systems in both models occurred under lateral rotation conditions: the MAEF model’s fixation system peaked at 77.025 MPa during right rotation, while the PSISF model’s fixation system peaked at 170.97 MPa during left rotation. Significantly, contrary to the PSISF model results, the fractured vertebral body (L1) in the MAEF model exhibited markedly higher maximum stress values during flexion and extension compared to lateral bending, left rotation, and right rotation. These values were comparable to the maximum stresses observed in the PSISF model during flexion and extension, a phenomenon attributed to the MAEF model’s micro-adjustable system. Additionally, under all loading conditions, the maximum stress values at the adjacent vertebral endplates in the MAEF model were lower than those in the PSISF model. Conclusion Theoretically, these biomechanical features of MAEF may lower the risk of implant failure and post-traumatic kyphosis and facilitate fracture healing, supporting its potential for minimally invasive treatment of thoracolumbar burst fractures.