Chapter 153 Minimally Invasive Posterior Cervical Foraminotomy and Microdiscectomy

Posterior cervical foraminotomy and microdiscectomy is a safe and effective procedure that can be used in the treatment of clinically significant foraminal stenosis resulting from lateral disc herniation or osteophytes. Symptoms improve in more than 90% of patients who undergo the procedure (Fig. 153-1).^1–8 Until the late 1950s, this was the predominant approach used in the treatment of herniated cervical discs. In 1958, however, Cloward⁹ introduced an anterior approach to cervical discectomy, and popularity with this technique grew as modifications to the technique made it safe and easier to perform. In addition, patients experienced less postoperative pain and muscle spasm, they had shorter hospital stays, and surgery could be performed through a smaller incision with less muscle trauma.

FIGURE 153-1 Sagittal (left), and axial (right) T2-weighted magnetic resonance image showing a lateral disc herniation at the C7-T1 level.

Numerous series show that patients achieve good relief from their symptoms with the anterior approach.^9–12 However, despite these advantages, the anterior approach is associated with the risk of numerous complications, including recurrent laryngeal nerve injury,^13–16 dysphagia and speech dysfunction,¹⁷ esophageal injury,¹⁸ and airway compromise,^19–21 as well as injury to the carotid artery²² and jugular vein.²³ In addition, anterior cervical discectomy has been implicated in both radiographic²⁴ and clinically significant adjacent segment degenerative disease,²⁵ as well as altering the native biomechanics of the cervical spine that may result from discectomy and fusion.^26,27

Because the posterior approach avoids a complete discectomy and fusion, it remains a viable option in the treatment of lateral soft discs or osteophytes in the cervical region, and superb decompression of the lateral recess and neural foramen has been well documented using posterior laminoforaminotomy.^1–5 This approach offers direct visualization of the exiting nerve root and avoids fusion, as is the case with anterior surgery.

Enthusiasm for the posterior approach is tempered by technical limitations that limit visualization of the distal foramen, in addition to generous bony and epidural venous bleeding. Significant muscle dissection also is necessary to obtain adequate surgical exposure, which increases intraoperative bleeding, as well as postoperative pain, muscle spasm, and hospital stay. Also, muscle denervation and retraction injury, as a result of stripping muscles from their point of attachment to the spine, recently have been shown to result in compromised biomechanical stability in the posterior cervical region.²⁸ Negative long-term effects similar to those that may occur with muscle injury during lumbar spine surgery^29–32 may also occur with muscle dissection during the approach to the posterior cervical spine.

As a result, posterior microendoscopic foraminotomy (MEF) was developed by Roh et al. to address cervical nerve root compression by direct visualization of pathology while minimizing tissue destruction upon exposure.³³ Muscle and ligamentous attachments to the spine are preserved, thus decreasing postoperative pain and spasm and helping maintain long-term stability. Finally, fusion and its associated sequelae are avoided.

Initial cadaveric studies using this technique demonstrated that the average vertical and transverse diameter of the laminotomy defect was identical for MEF or open techniques.³³ The average amount of facet removed and the extent of neural decompression was greater with MEF than with the open approach. Initial clinical results were quite favorable for the MEF procedure. Overall, the operative time, blood loss, length of hospitalization, and need for postoperative pain medications were all reduced with the MEF group compared with a similar group of patients who underwent the open procedure.³⁴ Within the MEF group, although some surgeons³⁵ advocate the prone position, we have found that changing from a prone to a semisitting position further improved these variables; compared with the open group, average operative time was reduced from 171 to 90 minutes and average blood loss was lowered from 246 to 28 ml. Moreover, the average hospital stay was reduced from 68 hours in the open group to 8 hours in the sitting MEF group.³⁴ Recently, many series of MEF have shown similar results.^33,36–40

We previously described our technique for performing a minimally invasive posterior cervical foraminotomy.⁴¹ As described here, lateral soft disc herniations can be treated using the MEF technique by performing a small resection of the superior medial pedicle, thereby allowing access to the herniated disc fragment. Over the last several years, we have preferred to use a microscope instead of an endoscope, because the microscope affords three-dimensional visualization of the anatomy as opposed to the endoscope, which is two dimensional. Other advantages of using the microscope over the endoscope include familiarity among neurosurgeons and improved optics for enhanced visualization of the operative field.

Positioning

Following routine presurgical evaluation and medical clearance, the patient is brought to the operating suite and general endotracheal anesthesia is induced. The patient is not given paralytics to visualize any muscular contraction resulting from nerve root manipulation. We routinely perform somatosensory evoked potentials to monitor the intraoperative integrity of the spinal cord. Electromyography of appropriate muscle groups can also be performed for additional intraoperative feedback. Preoperative antibiotics—either cefazolin or clindamycin, if the patient has a penicillin allergy—are administered 30 minutes prior to skin incision. Intravenous steroids are not routinely administered, and as a result of the short length of the procedure, a Foley catheter is generally not needed.

Initially in the supine position, the patient’s head is affixed to the Mayfield head holder, and the patient’s body is gradually brought to a semisitting position such that the knees are level with the heart. The Mayfield adaptor is attached to the table between the hips and the knees and arched back as necessary to accommodate the patient’s body habitus, connecting to the Mayfield head holder. Care is taken to maintain the neck in a comfortable, neutral position. The surgeon should be able to pass two fingers below the chin to assure adequate venous drainage via the jugular veins. The arms are folded and secured across the chest or supported at the sides; pressure points are padded to prevent nerve palsies and pressure sores (Fig. 153-2). Precordial Doppler monitoring is used to monitor air emboli in the right atrium; a central venous catheter is usually not necessary because of the brevity and minimal blood loss associated with the procedure.

FIGURE 153-2 Illustration of the semi-sitting position used for posterior cervical foraminotomy.

Approach

Under fluoroscopic guidance, a Kirschner (K) wire is carefully advanced toward the laminar facet junction. Care needs to be taken so that the K wire is not directed medially, where it can enter the interlaminar space and cause a spinal cord injury. It is therefore imperative to visualize the K wire and dilators as they approach the spine to prevent neurologic injury. In large, muscular individuals, we often stop advancing the K wire before docking on the facet and then pass the first muscle dilator, remove the K wire, and place subsequent muscle dilators and finally the tubular retractor, as shown in Fig. 153-3. Recent developments have resulted in minimal invasive muscle dilators that do not require a K-wire and subsequent muscle dilators to approach the spine (Fig. 153-4). This retractor system might help reduce iatrogenic neural injury.

FIGURE 153-3 These images illustrate progressive dilation of the soft tissue in order to create a working channel. This process begins with insertion of a K-wire (top left), and ends with the placement of the tubular retractor (bottom left). A straight curette is seen in the tubular retractor in the bottom left image, and is used to assist in docking onto the lamino-facet complex as described in the text and as seen in Figure 153-4.

FIGURE 153-4 Intra-operative lateral fluoroscopic images showing the use of the Nautilus retractor (Thompson MIS, Traverse City Michigan), used to approach the spine in a muscle splitting fashion without the use of a K-wire and subsequent muscle dilators. A,B: The retractor is advanced to the spine; C, D: docked and flaired open; E, F: and the tubular retractor passed over to dock on the spine.

Once the tubular retractor has been placed, a straight curette can be used to dissect through the muscles to the level of the facet complex. After the facet is palpated, the first and subsequent muscle dilators are used again and the working corridor is “redilated,” over which the tubular retractor is advanced again to dock closer to the facet complex. The tubular retractor must be positioned directly over the facet complex to facilitate dissection, as shown in Fig. 153-5. We typically use an 18-mm port, which we find provides sufficient exposure of the facet complex and ample working space. If needed, confirmatory anteroposterior views are also obtained with a K wire to ensure that the laminofacet junction of the desired level is adequately localized.³⁵

FIGURE 153-5 Highlighted area (in red, left) shows the area of interest. The right image illustrates correct positioning of the tubular retractor over the lamino-facet complex.

In heavyset individuals, or those with large shoulders, the surgeon may have difficulty localizing the correct level, especially when approaching the lower cervical spine. In this case, an anteroposterior image can be obtained and counting can proceed cephalad to the T1 level, identified by the first rib. It is therefore imperative that the surgeon be cognizant of anomalies such as a cervical rib during the presurgical workup.

Once the tubular retractor is adjusted to the desired position under fluoroscopy, it is then fixed to a flexible arm mounted to the operating table. The microscope is then brought into the field, and the rest of the procedure is performed under high magnification.

Surgical Technique

A Bovie cautery instrument on a long handle is used to circumferentially remove muscle from the operative field. It is best to work from lateral to medial and always be cognizant of the interlaminar space. The bony anatomy is further defined with a curette to appreciate the interlaminar space and facet relationship, as shown in Fig. 153-6. A 1- or 2-mm Kerrison punch is used to begin the laminotomy; this is extended laterally to complete the foraminotomy. It is often necessary to use a high-speed drill to help facilitate the foraminotomy. Epidural bleeding in this region is common but can be controlled with Gelfoam and cotton patties. Once the nerve root is visualized, a 45-degree, angled nerve hook can be used to palpate the neural foramen and confirm that the decompression is adequate, as shown in Fig. 153-7.

FIGURE 153-6 After removal of soft tissue, a curette is used to define the anatomy of the lamino-facet complex.

FIGURE 153-7 After lamino-foraminotomy has been performed, a 45 degree angled nerve hook is used to check the adequacy of nerve root decompression.

When performing a posterior discectomy, drilling approximately 2 mm of the superior medial pedicle facilitates safe removal of herniated disc fragments while limiting nerve root manipulation (Figs. 153-8 to 153-10). The space created by drilling the pedicle can also be used to reduce anterior osteophytes contributing to foraminal stenosis with the aid of a down-angled curette. Radiographic and tactile confirmation of the extent of discectomy or foraminotomy is obtained before closing.

FIGURE 153-8 Surgeon’s view illustrating the method by which the superior-medial aspect of the pedicle is drilled in order to gain entry to the disc space or anterior osteophytes.

FIGURE 153-9 Axial (left) and surgeon’s view (right) shows route of access to the disc space using a pediculotomy approach.

FIGURE 153-10 Decompressed nerve root.