CERVICAL STABILITY AFTER FORAMINOTOMY - A BIOMECHANICAL INVITRO ANALYSIS

Laminectomy or facetectomy of the cervical spine, or both, may be needed for decompression of the spinal cord or of the nerve-roots. Acute stability of the cervical spine was tested after laminectomy and progressive staged foraminotomies in an in vitro model. Twelve cervical spines from human cadavera were used in the experiment. Biomechanical testing included the application of an axial load, the application of a flexion and extension moment, and the application of a torsional moment. Each specimen was tested intact, after laminectomy of the fifth cervical vertebra, and after progressive foraminotomy of the sixth cervical root. Foraminotomy was performed by resection of 25, 50, 75, and 100 per cent of the facet joint and capsule. Torsional stiffness decreased dramatically when more than 50 per cent of the facet had been resected. Statistically equivalent subsets were the intact specimen, laminectomy, 25 per cent facetectomy, and 50 per cent facetectomy in one subset, and 75 and 100 per cent facetectomy in the least-stiff subset. Flexion-moment testing showed that the posterior strain did not differ among three groups: the intact specimens, those that had been treated with laminectomy, and those that had been treated with a 25 per cent facetectomy. The 50 per cent facetectomy resulted in a 2.5 per cent increase in posterior strain, and the 75 or 100 per cent facetectomy, in a 25 per cent increase in posterior strain compared with the intact specimen. Segmental hypermobility of the cervical spine results if a foraminotomy involves resection of more than 50 per cent of the facet. Thus, we recommend that, if a cervical foraminotomy is necessary, resection of the facet and stripping of the capsule be limited to less than 50 per cent of the facet.