Finite element modeling of cervical laminectomy with graded facetectomy.

In this study, an anatomically accurate three-dimensional finite element model of the human lower cervical spine (C4-C6) was used to study the biomechanical effects of cervical laminectomy with and without graded facetectomy. The intact finite element model was validated under flexion, extension, lateral bending, and axial torsion load vectors of 1.8 Nm magnitude. The moment rotation response of the finite element model matched well with experimental data. The gross external (angular motion) and the internal (superior and inferior intervertebral disc stress) responses were delineated under the four physiological loading modes for these iatrogenic changes. Results indicated that laminectomy markedly altered the cervical angular motion and the disc stress under flexion compared with all other loading modes. Facetectomy increased the angular motion and the inferior disc stress notably under flexion but did not affect the adjacent superior disc stress. Facet resection of > 50% caused pronounced increases in angular rotation and intervertebral disc stresses. These findings suggest that the resection of more than one-half of this structure may require additional procedures to restore the strength of the cervical column. Although gross external motion response can be obtained by experimental studies, the internal stress response can only be determined using mathematical models such as the finite element model used in the present study. The accentuated changes in the disc stress compared with the changes in the external rotation may be clinically relevant because increased internal load/stress can result in disc degeneration. The present three-dimensional finite element model offers additional information to better understand the extrinsic and intrinsic responses of the iatrogenically altered cervical spine.