Endoscopic Posterior Cervical Foraminotomy and Microdiscectomy

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Mick J. Perez-Cruet, Richard G. Fessler

Institute for Spine Care, Chicago Institute of Neurosurgery and Neuroresearch, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Ill., USA

Recently microendoscopic discectomy (MED) techniques have been applied to perform laminoforaminotomy and discectomy for unilateral cervical radiculopathy [1, 11] utilizing the MED technique and instrumentation (fig. 1) developed by Smith and Foley in 1997 for lumbar disc disease [4, 6]. The muscle-splitting approach used in this technique is effective in limiting postoperative pain and muscle spasms while maintaining the integrity of midline posterior muscular and ligamentous attachments to the spine. Minimally invasive posterior cervical microendoscopic discectomy and laminoforaminotomy (CMED) can provide a number of advantages including reduced approach-related morbidity, preservation of the motion segment, reduced patient postoperative pain and discomfort, and quicker patient recovery. In avoiding an anterior approach to the spine and maintaining segmental motion the incidence of hastened adjacent level disc degeneration may be reduced [3, 9, 10]. The muscle splitting approach used in this technique as apposed to the muscle stripping approach used in traditional posterior cervical discectomy and laminoforaminotomy may help to reduce paraspinal muscle denervation. Despite these many benefits there is a steep learning curve to mastering this technique, which may require additional training under the guidance of an experienced minimally invasive spine surgeon. Once trained in these techniques the results can be very satisfying for both clinician and patient. This chapter will focus on the technical considerations used in performing CMED effectively and safely.

Metrx Medtronic
Fig. 1. METRx instrumentation used for performing CMED with figures showing K-wire, sequential dilators and tubular retractor (a), endoscopic assembly (b), long tapered Drill (c), and specialized instruments (d).

Background

Posterior cervical foraminotomy and microdiscectomy is a proven effective technique for the management of lateralized herniated disc and foraminal stenosis [2, 5, 7, 8, 12, 17-19]. The endoscopic approach is a further evolution of this technique with a primary benefit of reduction in approach-related morbidity. This is accomplished with a number of tubular dilators that allows for muscle splitting of the longitudinal muscular fibers to reach the facet complex as opposed to striping the muscle from the spinous process and lamina and aggressively retracting the muscles laterally to gain access to the facet complex. The instrumentations used to perform this technique were originally designed for the treatment of lumbar disc herniation (fig. 1). The ability to perform CMED was first determined in cadaveric studies [16]. These studies determined that the METRx system could be used effectively to treat degenerative cervical disease and then was applied safely in a clinical setting [1, 11].

Evaluation

Patient workups routinely include plain anteroposterior, lateral and oblique x-ray views to determine spine alignment, disc space height and foraminal encroachment. Additional radiographic evaluation of the cervical spine will include either a magnetic resonance image (MRI) or myelogram, and/or computed tomographic myelogram (CTM) to visualize the area of neural compression. CTM is particularly helpful in multilevel degenerative cervical disc disease to determine the level of maximal neural compression since this study clearly shows bone pathology, as well as foraminal stenosis and nerve root compression. In conjunction with thorough clinical history and physical examination, radiographic evaluation will help to determine the operative level. Further assessment can include selective nerve root blocks and or electromyelographic studies. Ultimately, it is critical to correctly identify the anatomic level from which the patient's radiculopathy originates in order to achieve surgical success.

Indications

Endoscopic posterior cervical foraminotomy is indicated for cases of lateralized disc herniation (fig. 2), osteophyte compression, and foraminal stenosis. Ideally, patients should present with painful cervical radiculopathy, which correlates with neural compression seen on MRI, myelogram, and/or CTM. This procedure is not recommended for cases of cervical myelopathy from spondylosis or central disc herniation. Whereas traditional surgical teaching guides us to address pathology from an anterior approach when there is straightening or kyphosis of the spine, the endoscopic posterior approach can be used for cases of posterolateral disc herniation or foraminal stenosis with mild to moderate kyphosis so long as there is no evidence of instability. For these patients, particular caution must be taken to avoid resecting too much of the medial facet complex during the decompression. Studies have shown that

Fig. 2. Lateralized left C6,7 disc herniation ideal for treatment using the CMED approach.

up to 50% of the facet complex can be resected unilaterally without inducing iatrogenic instability [15]. Since the 30° angled endoscope allows for more extensive facet resection, care is taken during this procedure to avoid taking too much facet [16].

It is important to realize that even with a good clinical history of radiculopathy and a seemingly appropriate radiographic finding, a potential for misdiagnosis can exist. As the incidence of multilevel disc degeneration is high on MRI and CTM for elderly patients, it is statistically not uncommon that some degree of pathological change will be seen at any given level on imaging studies. For such patients, a careful search to exclude other causes of nerve root pain should be completed prior to operative intervention. The differential for nerve root pain includes spinal canal tumors, trauma, inflammatory diseases, demyelinating conditions, toxic and allergic conditions, hemorrhage, congenital defects, metabolic diseases, neuropathies, thoracic outlet syndrome, rotator cuff pathology, impingement syndromes, bursitis, arthritis of the shoulder, and bicipital tendonitis. It is important for spinal surgeons to be familiar with these disorders in order to properly exclude them from the list of possible etiologies before subjecting the patient to unneeded surgery. Electromyographic (EMG) and nerve conduction velocity studies done by a competent neurologist or physiatrist may be particularly helpful in this regard. Lastly, it is prudent to perform a psychological screening of all patients prior to performing this

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