Abstract:

Background: The facet joint orientation is a congenital anatomical factor of lumbar degeneration. Current biomechanical study generally based on an ideal model of the lumbar spine, the effect of the muscle has not been considered.

Purpose: We developed 2 normal human lumbar spine model (A and B, with or without psoas, L1-L5), changed the facet joint orientation into three conditions (F45, F50, F55). Submit the stress of disc under all of the models. Analyse the biomechanical influence of the psoas and fact joint orientation. Provide reference for some clinical problems such as degenerative lumbar scoliosis.

Method: A lumbar spine CT image of a normal person was used to develop the FE model by three-dimensional image modelling software Simpleware. Then import the model to Finite element software ABAQUS to complete the modelling, simulated the biomechanical reaction of lumbar in six motions including flexion, extension, lateral bending and torsion.

Result: Under flexion, the disc pressure of the model with psoas was 18.99% lower than the model without psoas, and 23.42% lower in extension. In lateral bending, the amount of reducing was 36.63% and 27.20% respectively. But in rotation, the changes of disc pressure was only 1.49% and 2.97%. In lumbar flexion and extension moments, model F55 showed the maximum intradiscal pressure. Model F45 showed the maximum intradiscal pressure in torsion moment. F45, F50 and F55 models have the similar intradiscal pressure in lateral bending.

Conclusion: Psoas major have obvious effects on lumbar spine under flexion, extension and lateral bending moment, but few under torsion moment. The patients with different facet joint orientation had different intradiscal pressure under six motions. The sagittal oriented facet joint made a higher pressure under flexion and extension moment, and the coronal oriented facet joint made a higher pressure under torsion moment.