Numerous options exist in the treatment of cervical radiculopathy and cervical spondylotic myelopathy, including nonoperative therapy and various forms of anterior and posterior decompression with or without stabilization. Although patient selection remains controversial, many of these patients benefit from a surgical decompression. Compared with anterior cervical approaches, traditional “open” methods of posterior decompression are generally associated with fewer complications but cause more postoperative neck pain and greater risk for destabilization of the spine. The recent application of minimally invasive techniques has enabled surgeons to maintain the advantages of the posterior approach whereas minimizing the disadvantages and not compromising safety. This chapter contains a discussion of these issues and detailed descriptions of two minimally invasive posterior cervical decompression procedures, the cervical microendoscopic discectomy/foraminotomy (CMED/F) and the cervical microendoscopic decompression of stenosis (CMEDS), as developed by the senior author.
The indications for CMED/F are the same as for open posterior cervical discectomy/foraminotomy: radiographic compression of a cervical nerve root with a corresponding clinical radiculopathy and intractable pain, progressive neurologic deficit, or a failure to respond to conservative therapy.
The indications for CMEDS are the same as for open posterior cervical procedures to treat cervical spondylotic myelopathy: radiographic spinal cord compression with clinical myelopathy in selected patients.
Traditional posterior cervical decompression procedures are effective but can result in significant postoperative neck pain, chronic neck pain, and progressive kyphosis in a number of patients.
Decompressions ranging from unilateral foraminotomies to three-level bilateral decompressions can now be performed using a unilateral minimally invasive approach.
CMEDS and CMED/F are as effective as open procedures but cause less perioperative pain and have the potential to produce better long-term outcomes through avoidance of iatrogenic chronic neck pain and predisposition to progressive kyphotic deformity.
Because of the vulnerability of the spinal cord, sequential dilation of tubular retractors in the cervical spine requires additional care. We recommend using a K-wire only as far as the cervicodorsal fascia, cutting the fascia under direct vision, and then using the smallest dilator to locate the surface of the facet joint.
Contralateral decompression is not as forgiving in the cervical spine as in the lumbar spine and requires minimal dural manipulation.
Degenerative disease of the cervical spine can cause compression of neural elements through disc herniation, ligament and facet joint hypertrophy, and formation of vertebral body end-plate osteophytes. The effects of these changes can be exacerbated by a congenitally narrow spinal canal, segmental instability, and deformity. These dynamic processes can contribute to clinical radiculopathy, myelopathy, or both, depending on the degree to which nerve roots or the spinal cord is affected. Surgical decompression is indicated for selected patients with neurologic signs and symptoms of radiculopathy and myelopathy, and corresponding radiographic evidence of compression. The cervical spine can be decompressed through an anterior or a posterior approach, both of which have relative advantages and disadvantages. Although the choice of approach is sometimes relatively clear, often the problem can be addressed from either direction, with the ultimate decision balancing the risks and benefits of each. The application of minimally invasive techniques carries the promise of reducing the major morbidities of the posterior approach for many indications without compromising its numerous advantages.
NEED FOR A MINIMALLY INVASIVE POSTERIOR CERVICAL DECOMPRESSION
The fundamental tenet of minimally invasive surgery is a reduction of approach-related morbidity. Functional assessments of patients after cervical decompression have focused primarily on neurologic outcomes; however, iatrogenic, approach-related morbidity can have significant short-term and long-term consequences and impact postoperative functional status. For simple unilateral radiculopathy, many surgeons prefer a one-level anterior cervical discectomy and fusion over posterior cervical foraminotomy and discectomy, although both are equally effective. Avoidance of the postoperative pain associated with the posterior approach is a major factor mitigating this choice, despite the increased cost of the anterior cervical discectomy and fusion, the potential risk for damage to anterior cervical structures, and the potential for contributing to adjacent segment disease. The advent of cervical arthrodesis has obviated some but not all of these issues.
Although axial neck pain is a widely recognized presenting symptom of cervical spondylosis, neck pain is often not specifically evaluated when assessing outcomes after posterior cervical procedures. Although neck pain in the immediate postoperative period is a universally recognized drawback to the posterior cervical approach, it is often de-emphasized because it is considered to be temporary. In fact, chronic neck pain is an under-recognized, approach-related chronic sequela, particularly in patients who have undergone a multilevel decompression for Cervical Spondylotic Myelopathy (CSM) . In patients with laminoplasty, for example, reported rates of chronic postoperative neck pain after at least 3 months of follow-up range from 3% to 25%, to as high as 50% and 60%. If iatrogenic neck pain after posterior cervical surgery could be eliminated or reduced, the posterior cervical approach would be better tolerated both in the short term and the long term, and functional outcomes of surgery for CSM could potentially be improved.
Another serious issue after posterior cervical decompression is the predisposition to progressive kyphosis. Posterior cervical laminectomy can destabilize the spine through the removal of the lamina, spinous processes, and interspinous ligaments (the so-called posterior tension band), and a variable degree of facetectomy. The degree of destabilization is thought to be related to the number of levels decompressed, the amount of the facet complex removed during decompression, younger age, and the preoperative sagittal alignment. One study found development of kyphosis in 21% of patients with a straight or lordotic cervical spine after laminectomy for CSM. Another found 36% of patients with noticeable changes in sagittal balance, and 14% with the development of a significant deformity after laminectomy.
Muscle-splitting tubular retractor systems and improvements in endoscopic technology and associated instruments have allowed for the application of minimally invasive techniques to posterior cervical decompressive procedures. The microendoscopic cervical foraminotomy/discectomy (CMEF/D) was first described in a cadaver model that demonstrated the ability to achieve equivalent bone removal and nerve root exposure when directly compared with open technique. It differs little from the open procedure after soft-tissue exposure, and its safety and efficacy have been shown in case series. The cervical microendoscopic decompression of stenosis (CMEDS) is a related, more recently developed procedure that enables bilateral posterior decompression from one to three levels using the same small muscle dilating retractor, hemilaminar approach, and a single 1.8-cm skin incision. Other reported minimally invasive posterior approaches to treat CSM include minimally invasive laminoplasty and endoscopic bilaminar approach. Although outcomes from both procedures appear excellent, the former suffers from technical difficulties related to elevation of lamina and strut placement, and the latter entails a more invasive soft tissue and bony exposure than the procedure described here.
INDICATIONS AND CONTRAINDICATIONS
All patients who are candidates for an open posterior cervical foraminotomy/discectomy are candidates for a CMEF/D. These are patients with a clinical radiculopathy and radiographic evidence of foraminal stenosis and/or a lateral disc herniation compressing the corresponding nerve root. For a recommendation to surgery, patients must have intractable pain, a significant neurologic deficit, or have responded unsuccessfully to conservative management. Most patients who are candidates for a noninstrumented, posterior cervical decompression are also candidates for a CMEDS. These are selected patients with clinical myelopathy, radiographic evidence of spinal cord compression from one to three adjacent cervical levels, and a lordotic cervical spine. Relative contraindications are loss of the normal cervical lordosis and bulky ventral disease, particularly if the ventral disease is contained to one or two levels. With current technology, such patients are better served by an anterior cervical discectomy and fusion. Other contraindications are greater than three-level disease, which may require an open posterior decompression, and segmental instability and/or kyphosis, which may require a fusion in addition to a decompression.
General surgical indications for patients with CSM are nuanced and determined on a case-by-case basis. In cases of progressive myelopathy, surgical decompression is almost universally indicated. For patients with mild, stable radiographic and clinical disease, the decision on whether to proceed with surgery is made after a careful discussion of the natural history of the disease, realistic expectations of surgery, and the risks of the procedure. Given the unpredictable and potentially devastating nature of CSM exacerbations and the low morbidity of the procedure, many surgeons are uncomfortable advising against surgery, even in patients who are mildly symptomatic or who are asymptomatic but have clinical signs of myelopathy and evidence of spinal cord compression on imaging studies.
General endotracheal anesthesia is induced on a standard electric operating table. A neurophysiologic monitoring is put in place. Routine perioperative antibiotics are administered, as are intravenous corticosteroids at the surgeon’s discretion. The table is then turned 180 degrees relative to the anesthesiologist. The patient’s head is fixed in a Mayfield head holder. The table is manipulated to place the patient in a semi-sitting position with the head flexed and the neck straight and perpendicular to the floor ( Fig. 42-1 ). Although the procedure can be performed in the prone position, the sitting position is preferred because it confers advantages of decreased epidural bleeding, decreased pooling of blood in the operative field, decreased anesthesia time, and gravity-dependent positioning of the shoulders for better lateral fluoroscopic images.