[Effects on single segmental lumbar stability after graded facetectomy and laminectomy: a finite element study].

OBJECTIVE: To explore the effects on degenerative single segmental lumbar spinal stability after posterior graded laminectomy and facetectomy by a finite element method.

METHODS: A finite element model of L3-S1 segments with a single segmental degeneration at L4-5 level was established. Different models of L4-L5 segmental instability after posterior graded laminectomy and facetectomy were established. And interior 1/3, 1/2, 2/3 of laminar and bilateral facet joints were resected. Physical loads were applied to the models and the changes of range of motion (ROM) at L4-5 level in different models were recorded during flexion, extension, lateral bending and rotation.

RESULTS: As compared to preoperative model, after resecting 1/3 bilateral facet joints at L4-5 level, L4-5 segmental ROM increased 18% during flexion, 27% during extension and 45% during torsion. And the increased degree of ROM became more obvious along with a greater resection range of bilateral facet joints. No significant difference existed in L4-5 segmental ROM during lateral bending in all models.

CONCLUSION: Facet joints play vital roles in lumbar segmental stability. And segmental instability may occur when 1/3 bilateral facet joints are resected.