Lumbar Spine FEA

Spinal Fusion

Spinal fusion has been the standard method for clinical and mechanical stabilizationof the lumbar spine. Spinal fusion consists of using implanted medical devices, including fusion cages and/or fusion rods to restrict motion across one or more spinal segments. By restricting segmental motion, bone growth across the segment is encouraged and mechanical triggering of pain sensing nerves (nociceptors) due to abnormal spinal motion is hopefully reduced. One of the consequences of spinal fusion is adjacent segment degeneration (ASD), which is the development of degenerative conditions in the neighboring vertebra.

Dynamic Stabilization Devices

Dynamic stabilization devices are used as an alternative to spinal fusion, and theoretically reduce the risks of ASD associated with spinal fusion. Dynamic stabilization devices also allow the spine to move, but restrict motion extremes that are more likely to mechanically trigger nociceptors.

Lumbar Spine Mesh Model

As part of the research, the geometry of L3 and L4 was modified to include pedicle screw holes. The dimensions of the screw holes approximate a typical pedicle screw for the lumbar spine. L1 through L5 were then meshed with hexahedral elements. The lumbar spine mesh is shown in the figure to the left.

The finite element model of the lumbar spine, including the dynamic stabilization device and pedicle screws will be tested in flexion, extension, and axial rotation using LS-Dyna (LSTC, Livermore, CA). In the finite element model, the dynamic stabilization device will be inserted at the L3-L4 segment to study the effects on the adjacent segments (L2-L3 and L4-L5). A non-linear solver must be used due to the large strains that develop in the intervertebral discs, the highly nonlinear material behavior of the spinal soft tissues and the nonlinear contact conditions at the facets.

The results from the finite element model will be compared to test results of the FlexSuRe installed on a cadaver spine. This data can be used to validate the finite element model.