ArgoSpine: Cervical Stenosis: Treatment Strategy, Surgical Approach and Technique
BY EDITOR, DECEMBER 4, 2007
The article below was first published in ArgoSpine News in December 2006. As part of our sponsorship of ArgoSpine, we're republishing select ArgoSpine News content for our audience. This article, originally published in December 2006, was written by Paul R. Cooper, M.D., Professor of Neurosurgery at New York University Medical Center.
Indications for Operation
Radiographic demonstration of cervical spondylosis is present in 25-50% of patients by the age of 50 and in 75-85% of patients by the age of 65. Nevertheless only a small minority of patients present with signs and symptoms of cervical spondylotic myelopathy. Thus the imaging findings of cervical spondylosis by themselves are not an indication for operation. In order to be considered as a candidate for operative decompression, patients must have motor and sensory symptoms or objective deficit as well as evidence of spinal cord compression on imaging studies. While patients who are neurologically intact with imaging findings of spondylosis are frequently advised that prophylactic operation is indicated to prevent catastrophic spinal cord injury after a fall or a motor vehicle accident there is no data on the risks versus benefits of this strategy.
Once patients develop myelopathic signs or symptoms operation is indicated but the choice of operative approach depends on the number of spinal segments involved, whether compression is predominantly from anterior or posterior, the extent of compression above and below the disc space, and the sagittal alignment of the cervical spine.
The Anterior Approach
Choice of procedure
The anterior approach is ideal for single level spondylotic compression or two level adjacent spondylosis, or ossification of the posterior longitudinal ligament (OPLL) extending no more than two vertebral bodies. Vertebrectomy is appropriate for patients with OPLL or patients with osteophytes at adjacent levels. In patients with osteophytes from spondylosis at adjacent levels, either two level osteophytectomy or vertebrectomy may be performed although there is ome evidence that lordosis is better maintained with two level excision of osteophytes. In patients with extensive OPLL, multilevel vertebrectomy will be effective in decompressing the spinal cord but the greater the number of vertebrae removed (without supplemental posterior instrumentation) the higher the chance of graft and plate failure. Anterior plate and screw design have advanced greatly in the past two decades from unlocked to locked rigid screw-plate systems, semi-rigid systems and most recently to systems which allow for translation of the plate in relation to the screws. This allows for settling of the graft and maintenance of shared load between the graft and plate minimizing stress on the screws or plate and is particularly useful in multilevel vertebrectomies.
Neurological outcome
Neurological outcome after anterior decompressive outcome in our patients in a series which has been published previously has been gratifying. Between 79 and 89% of muscle groups with abnormal function preoperatively improved, mean mJOA score improved from 12.4 to 14.9. Using the Cooper Scale which evaluated upper and lower extremities separately 47% of patients with abnormal upper extremity function improved and 75% of patients with abnormal lower extremity function improved.
The Posterior Approach
Indications
The posterior approach is technically easier than the anterior approach and is ideal for patients with a lordotic spine with compression at more than two disc spaces or two vertebral bodies (in the case of OPLL). It is contraindicated in patients with kyphosis as the spinal cord will not move posteriorly away from anterior compressive lesions. It is also contraindicated in patients with midline soft cervical discs compressing the spinal cord.
Choice of procedure
In considering the posterior approach, the surgeon has the choice of laminectomy alone, laminectomy with posterior instrumentation, or laminoplasty. All of the posterior approaches have the disadvantage of not removing the offending pathology but if the spinal cord moves posteriorly away from the compressive lesion this is of little consequence. A certain percentage of patients who have laminectomy will develop kyphotic deformity. This is more likely to occur if the facets are resected, and if pre-existing instability is present.
Laminectomy and posterior instrumentation
By combining laminectomy with interfacet fusion and posterior instrumentation utilizing screw/plate or screw/rod constructs, the spine is stabilized and kyphotic deformity will not occur. It is also advantageous because osteophyte progression likely ceases once the spine is fused. If anterior operation should become necessary at a future time for residual compression or growth of OPLL the spine is stable and anterior graft or instrumentation failure is unlikely. For OPLL in particular, the posterior approach avoids the complications of long anterior decompression: graft extrusion, plate loosening, esophageal dysfunction, and dural tears and cerebrospinal fluid fistulae. Posterior fixation of the cervical spine was revolutionized by Roy-Camille who developed plates and screws for the fixation at the lateral masses. The original plates were rudimentary, could not be bent, were limited in length and had a fixed inter-hole distance making them difficult to use for multilevel fixation. Subsequent development of lateral mass plates by others produced plates that could be bent to the contour ofthe spine and were sufficient in length for stabilizing the entire cervical spine with holes spaced from 11 to 15 mm apart. Subsequent development of polyaxial screw/rod devices allowed more versatility and more accurate placement of screws in the lateral masses.
Laminoplasty
Laminoplasty has been advocated as a preferred means of posterior decompression. Advocates claim that it is superior in maintaining normal alignment, maintains normal motion, and prevents postoperative spinal cord compression by a laminectomy membrane. To the ocntrary there is no data in the literature supporting any of these claims as will be discussed in a subsequent session of this meeting.
Outcome
We have reviewed our results with laminectomy and posterior instrumentation in a series of 38
patients with OPLL or cervical spondylotic myelopathy. The mean mJOA score improved from 12.9 to 15.6, 96% of muscle groups with less than 5/5 strength improved, gait improved in 94% of patients and all patients had at least some improvement in sensory function.
Combined anterior and posterior approach
Occasional patients require a combined anterior and posterior approach. Patients with spondylotic myelopathy and kyphotic deformity who require a multilevel vertebrectomy to achieve adequate decompression may also require posterior instrumentation to further stabilize the spine and prevent anterior graft and plate failure.
Conclusions
In summary anterior operation is indicated for compression by soft disc, osteophyte or OPLL at one or two vertebral levels. For greater than two levels of compression by osteophyte or OPLL in a patient with a lordotic spine posterior decompression and stabilization will achieve excellent results. Anterior operation is indicatedfor decompression and correction of kyphotic deformities and should be combined with posterior instrumentation after multilevel vertebrectomies to minimize the incidence of plate and graft complications.
