Faculty Bibliography

The exact size of the bony cervical spinal canal and the vertebral body was measured in 368 cadaveric adult male vertebrae. A comparison of radiographic and direct measurements was also undertaken. The mean sagittal diameter of the spinal canal for C3-C7 was close to 14 mm (14.07 +/- 1.63 mm; N = 272). The mean ratio of the sagittal canal diameter to the vertebral body diameter (canal to body ratio) was 86.68 +/- 13.70 mm. Thirty-one percent of subaxial vertebrae would be diagnosed as having spinal stenosis if a canal to body ratio of less than 80% was considered abnormal. Measurements from plain radiographs overestimate the canal diameter. The average diameter for the lower cervical spinal canal is about 14 mm. The canal to body ratio is independent of radiographic magnification, but may produce misleading results

The long-term success of surgical management of spinal stenosis by decompressive lumbar laminectomy is predicated partly by the maintenance of intervertebral stability. Excessive bone removal, especially of the pars interarticularis, may predispose the spine to iatrogenic segmental instability and spondylolisthesis. Removal of too little bone may be inadequate to relieve stenotic or radicular symptoms. Wide decompression with concomitant arthrodesis has been advocated, but arthrodesis compounds the surgical complexity and increases the risks of surgical treatment. Internal lumbar laminoplasty obviates the problem of too little or too much bone removal in the surgical management of spinal stenosis. The spinal canal is enlarged internally by an undercutting facetectomy performed through a narrow central laminectomy. The pars interarticularis is left completely intact. Twenty five adult human cadaveric spinal units were subjected to biomechanical testing following hemilaminectomy, total laminectomy, internal laminoplasty, partial facetectomy, or disk transection and internal laminoplasty. Analysis was performed after video and computer acquisition of data from specimen testing on an Instron machine. Internal laminoplasty demonstrated more intrinsic stability than the other surgical procedures

It is widely believed that brain stem dysfunction and cranial nerve palsies in patients with rheumatoid arthritis (RA) are common and related to the vertical translocation of the odontoid process. In our database of 235 patients with seropositive RA and craniocervical junction involvement, we have found a very low incidence of such problems. Long tract signs were common, but loss of proprioception (joint position sensation) as the sole neurologic deficit was rare. Nystagmus was found to be associated with the tonsillar herniation of a Chiari 1 malformation and loss of joint position sensation with severe compression of the posterior aspect of the spinal cord at the craniocervical junction. The implications for posterior occipitocervical fusion, particularly by sublaminar wiring, are discussed

A modified transthoracic approach to the thoracic vertebral column is described. In this method, the parietal pleura is detached from the chest wall and retracted with the visceral pleura and its contents. A direct approach to the vertebral bodies is thus achieved without transgression of the intrapleural space. The technique can be extended to include exposure of the thoracolumbar spinal column, utilising a thoracoabdominal approach with extrapleural and extraperitoneal dissection. Management of the costophrenic detachment is thus simplified. This approach has significant advantages for orthopaedic, vascular and neurosurgical procedures

A study was conducted to determine the ability of demineralized bone matrix gel to act as an osteoconductive/osteoinductive material to enhance canine spinal fusion. Seven dogs underwent posterior spinal fusion. Four-level fusions were performed with one of four procedures at each level: decortication alone, with gel added, with autograft, or with both gel and autograft. Dogs were killed at 6 weeks and early histologic response was studied. At untreated control sites, little bone formation was evident. Gel-filled sites showed abundant osteoid, with 60% of demineralized particles fused to or surrounded by new bone. Sites filled with autograft had more new bone, but there was more osteoid at gel-treated sites. Autograft augmented with gel showed the most vigorous response, with extensive bridging between demineralized particles, host bone, autograft, and new bone. Significantly less autograft was needed to induce a similar amount of new bone formation when gel was added. Use of the gel as an autograft extender may improve the chance for successful spinal fusion

The atlantoaxial articulation is a multiaxial joint with a freedom of motion that presents unique problems in achieving surgical stability. Several methods of atlantoaxial arthrodesis have been established with varying degrees of immediate and sustained stability and safety. This study describes a new, improved method of posterior atlantoaxial arthrodesis, using (Halifax) interlaminar clamps with interposed bone graft, which provides distinct benefits over existing techniques. This method achieved atlantoaxial union within 12 weeks in 80% of the study's patients (20/25). The clamp fixation was revised in two patients, with subsequent fusion. Three other patients required revision surgery for nonunion due to loosening of the clamp. This was usually caused by incomplete tightening of the screws, with subsequent loosening or dislocation of the device. Possible clamp loosening is a potential problem with the currently available system, and may be a result of the clamp design. Techniques to minimize this risk and suggestions for improvement in the device are discussed. Nonunion is more likely to develop in patients with rheumatoid arthritis. If nonunion occurs, the pseudarthrosis is generally between the posterior bone graft and the ring of C1

The cervical spine contains 31 joints and moves about 600 times per hour. This makes it a site with a predilection for synovitis, ligamentous inflammation and mechanical stress in all types of chronic arthritis. Accordingly, eight different atlantoaxial or subaxial sublaxations and numerous other pathologic conditions occur in this area. The vital structures contained in this area impart particular significance to this involvement. Because there are practically no similarities between the structure and function of the lumbar spine and cervical spine, no parallels can be drawn between these two anatomically separate sites. Therefore, the anatomy, physiology, pathology, clinical syndromes, and treatment of the rheumatoid cervical spine have to be understood and dealt with on their own. This review article contains an update of topics of utmost importance in patient care, in light of the most recent basic and clinical science studies. Particular attention has been paid to new imaging and neurophysiologic techniques and their relevance to clinical design and treatment decisions, and modes of treatment in light of new advances in surgical technique and in our understanding of the long-term effects of active expectance and surgical intervention

Compression of the neuraxis may occur after displaced fractures of the dens. Nonunion or malunion increases the risk of developing neurologic complications because of the resulting atlanto-axial instability. Posterior decompression has generally been the surgical solution to myelopathy at this level. Two patients with cervical myelopathy due to displaced ununited dens fractures were treated with posterior fossa decompression and high cervical laminectomy. Both patients deteriorated after the surgery. Most of their neurologic deficits finally resolved after microsurgical transoral decompression (by resection of the dens). In those patients in whom atlanto-axial instability causes primarily anterior compression of the neuraxis, especially by a bony lesion, decompression posteriorly may not achieve the desired effect, and, instead, may cause a deterioration in the patient's condition. Anterior atlanto-axial subluxation effectively lengthens the bony spinal canal, which results in stretching of the relatively inelastic spinal cord over the bony deformity. If indirect methods of reduction fail to relieve the condition, then anterior transoral decompression is recommended

Fractures which occur near the base of the dens have a low propensity to unite spontaneously. One of the major complications of nonunion is displacement of the fracture resulting in neuraxis compression and the development of myelopathy. Hypertrophic nonunion of the dens may cause spinal cord compression even if displacement does not occur. This situation has not to our knowledge previously been reported. A literature review and appraisal of the issues raised are discussed. Appropriate therapeutic options are outlined, including posterior surgery and the use of transoral decompression