Cervical Stability after Foraminotomy

Laminectomy or facetectomy ofthe 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 SO 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. Decompression of the cervical spinal cord and cervical-nerve roots can be accomplished through an anterior or posterior approach. Posteriorly, laminectomy is needed for decompression of the cord and foraminotomy is needed for decompression of the nerve-roots. A portion of the cervical facet (zygapophyseal) joint must be re*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study. tUniversity of Wisconsin, 600 Highland Avenue, Madison, Wisconsin 53792. Please address requests for reprints to Dr. Zdeblick. sected in order to expose and decompress the nerve-root. A laminectomy and foraminotomy effectively decompresses the cord and roots, but it may render the spine unstable, leading to progressive kyphosis and worsening of the patient’s neurological status3’’4. Cattell and Clark described the development of angular deformities in children soon after a laminectomy for the treatment of a tumor. Mikawa et al. noted a 14 per cent prevalence of kyphosis after cervical laminectomy for the treatment of spondylosis in sixty-four adults. Clinical treatment at this stage may be quite difficult’2. The problem of acute instability of the cervical spine after resection of a facet has been investigated in several previous studies4’’#{176}’2’3. However, these investigators tested specimens that consisted of a single motion segment, tested the specimens to failure, or tested only specimens in which the facet had been completely resected. Instability after partial facetectomy usually is not due to fracture of a facet but to progressive subluxation. Therefore, testing to osseous failure does not appear to be physiological or appropriate. Testing of single vertebral motion segments also may not be appropriate because it unduly constrains the motion of the cervical spine. The present study was designed to test the acute stability of the cervical spine after laminectomy and progressive staged foraminotomies. The goal of the study was to determine what degree of resection of the facet led to acute instability after application of physiological loads to a model consisting of the third through seventh vertebral bodies. Materials and Methods The cervical spines of twelve human cadavera were obtained. The age at the time of death had ranged from thirty-two to sixty years and averaged forty-seven years. Initially, radiographs were made of all specimens to screen for metastatic disease. The Spines were then frozen at -20 degrees Celsius until the day of testing. On the day of testing, the Spines were thawed at room temperature and cleaned of all soft tissue, with the osseous and ligamentous structures left intact. Care was taken to preserve the facet capsule during preparation of the specimen. All biomechanical testing was completed within three hours after the specimen had been thawed. The specimens were rigidly fixed with transfixing pins at the third and seventh cervical vertebral bodies.