Load Sharing in L4-L5 Spinal Motion Segment Using an Asymmetrical Finite Element Model

Lumbar spine degeneration diseases require precise prediction of biomechanical parameters. These parameters include stress in ligaments, intradiscal pressure and facet loads. For this purpose, several symmetrical FE models of lumbar spine have been proposed previously with inherent simplifications in design. Such models may not give realistic results for biomechanical analysis because of the assumptions in their design. An asymmetrical 3D finite element L1-L5 lumbar spine was developed using computed tomographic scans of a healthy individual. All lumbar spinal elements were added to the model, including vertebra, intervertebral discs, ligaments and facet joints. 400N pre-compression load was applied and model was simulated at 10Nm pure moment in all six planes of motion. L4-L5 motion segment was used for prediction of biomechanical parameters. Facet loads reached the maximum value of 200N in extension and axial rotation. Intradiscal pressure had highest value in lateral bending where it was predicted as 2.3MPa. Flexion showed significantly higher pressure of 1.67MPa in disc. Stress in interspinous ligament had maximum value of 3.27MPa in flexion motion whereas capsular ligament had maximum stress value of 29MPa in extension motion. Based on these predictions and literature values, it is concluded that facet joints and capsular ligaments are effective in load sharing during extension motion. Interspinous ligaments are utilized during flexion while intervertebral discs performed load sharing in lateral bending, axial rotation and flexion.