[The finite element analysis of lumbar fusions]

To investigate the stability and the stress distributions of L(3-5) fused with three different approaches (interbody, posterolateral and circumferential fusions) and to investigate degeneration of the segment adjacent to the fused functional spinal unit.

A detailed L(3-5) three-dimensional nonlinear finite element model of a normal man aged 32 was established and validated. Based on the model, the destabilized model, the interbody, posterolateral and circumferential fusions models of L45 were established. After the loadings were placed on all the models, we recorded the angular motions of the fused segment and the Von Mises stress of the adjacent intervertebral disc.

The circumferential fusion was most stable than the others, and the interbody fusion was more stable than the posterolateral fusion. The maximal Von Mises stress of the adjacent L3.4 intervertebral finite all the models was ranked descendingly as flexion, lateral bending, torsion and extension. For the three kinds of fusions, the stress increment of the L34 intervertebral disc was ranked ascendingly as interbody fusion, posterolateral fusion and circumferential fusion.

After destabilization of the L(4.5) segment, the stability of the circumferential fusion is better than that of the others, particularly under the fluxional or extensional loading. The stability of the interbody fusion is better than that of the posterolateral fusion, except for under the fluxional loading. The feasibility of adjacent segment degeneration can be ranked descendingly as: circumferential fusion, posterolateral fusion and interbody fusion.