Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture

OBJECTIVE: The thoracolumbar (TL) area marks the transition of the rigid thoracic spine into the mobile lumbar spine, and it is considered to be the weakest part of the spine. This study was designed to develop a finite element (FE) model of the TL junction (T9-L3) to provide data that could help the clinician and researcher to answer the question of whether short-segment posterior fixation is sufficient for biomechanical performance. In addition, the aim was to examine whether long-segment posterior fixation carries a greater risk of the development of adjacent segment disease. METHODS: This was a biomechanical finite element model analysis. FE analysis of the spine was conducted with posterior instrumentation under multidirectional loading conditions in order to evaluate the kinematics of the instrumented lumbar spine, as well as stresses in the posterior spinal instrumentation. We analyzed the following: 1) the range of motion of the T9-L3 region; and 2) the von Mises stress nephograms of the pedicle screws, rods, vertebrae, endplates, and intervertebral discs of 2 fixation FE models. RESULTS: Long-segment stabilization was found to be beneficial in terms of reducing total stress on the spine. However, it is possible to reduce the stress on the system by incorporating the spinal fracture into the stabilization system. Therefore, short-segment stabilization is sufficient to create a safe and robust stabilization system and to maintain neighboring intact vertebrae. CONCLUSIONS: Short-segment posterior fixation is sufficient to stabilize fractures at the TL junction, where the spinal fracture is included in the stabilization system.