Biomechanical Study And Finite-Element Evaluation Of Share Loads On Lumbar Facet Joints

Biomechanical study and finite-element evaluation ofshare loads on lumbar facet jointsAbstractObjectives:(1) To study the share loads of lumbar facet joints (L3-L4 and L4-L5) in all kinds of motions of lumbar spine and evaluate the role of facets in lumbar spinal stability. (2) To study the effects of disc excision to the same and the adjacent facet joints and analyse the mechnism of low back pain after disc excision. (3) To build a L4-L5 motion segmeng three-dimension finite-element model and analyse the role of facet joints in the load sharing. Materials and methods: (1) Eight fresh young men's cadaveric lumbarsacral spines were examined on MTS 858 system. Various of motions were simulated by changing the loads through MTS or the jigs under the specimens. These motions included: neutral, flexion ~ flexion 200, extention 100, extention 200, axial rotation (left and tight) 100, left and right bending iS0. The compressue force on both sides of facet joints of L3-L4 and L4-L5 segments were examined by pressure-sensitive film. (2) The force of facet joints after L4-L5 disc excision were examined again by pressure sensitive film. Then the effects of disc excision to the same and adjacent facet joints were accessed. (3) A three-dimension finite-element model was built by computed tomography (CT) scanning. Contact loads under axial compress loads and pure 8Nm flexion and extention moments were examined before and after disc excision. Results: (1) About 15 per cent of the compressive force is carried by the facet joints in the erect standing position. In flexion position the pressure decrease companied by the angle increase. In extention position the situation is opposite. In 1iending position the pressure was examined and the magnitude of pressure are equal on both sides. In axial rotation the pressure was the largest while only the opposite side could bear the loads. In all kinds of position the pressure on both L3-L4 and L4-L5 segments is equal. (2) After disc excision the pressure on the facetjoints of L4-L5 segment increase in erect standing or fexion or extension-3-positions. It is the same one in bend position. But the pressure decrease about 50 per cent in axial rotation. The fact joints of L3-L4 segment increase in flexion and extension 200 positions and decrease in axial rotation. (3) The results got by finite-evaluation and pressuer sensitive film were accordant in general. But in current study we only compare the erect standing and flexion, extention positions. Conclusion: (1) The facet joints play a considerable part in resisting the intervertebral loads. The intact lumbar spine facet joints bear the largest luads in axial rotation, then followed the extention position. In erect standing the facet joints carry about 15 per cent compressive force. (2) After disc excision not only the same segment, but also the facet joints in the adjacent segment have to carry more quantity of loads. It may be a considerable cause of low back pain after surgery. (3) In this study a L4-L5 three-dimension finite-element model was established. It is accurate and credible.