Minimally Invasive Decompression of the Cervical Spine

Degenerative disease of the cervical spine can cause compression of neural elements through disk herniation, ligament and facet joint hypertrophy, and the formation of vertebral body end plate osteophytes. A congenitally narrow spinal canal, elements of segmental instability, and the presence of deformity can exacerbate the effects of these changes. These dynamic processes can contribute to or exacerbate radiculopathy, myelopathy, or both, depending on the degree to which the spinal cord or nerve roots are affected. Many patients with radiculopathy or stable myelopathy can be treated with appropriate nonoperative measures. Surgical decompression is indicated for patients with neurologic signs and symptoms of radiculopathy or myelopathy with corresponding radiographic evidence of neural compression and for whom nonoperative management has failed.

The cervical spine can be decompressed through either an anterior or a posterior approach, each of which has relative advantages and disadvantages. Many surgeons still consider anterior cervical diskectomy and fusion the gold standard for the treatment of cervical disk radiculopathy, myelopathy, or myeloradiculopathy, but motion-preserving techniques—including disk replacement, posterior cervical foraminotomy, and posterior decompression with laminectomy or diskectomy—have become increasingly popular. These minimally invasive surgical (MIS) techniques can even be used to approach intradural pathology, or they can be combined with percutaneous fusion techniques as the situation arises. The choice of approach is sometimes relatively clear; however, the problem often can be addressed from either direction, with the ultimate decision balancing the risks and benefits of each method. Over the past few decades, the MIS and percutaneous techniques have been shown to preserve healthy tissues, better maintain intact spine biomechanics, shorten hospital stays, cause less postoperative pain, enable faster patient mobilization, reduce complications, reduce operative blood loss, and possibly even lead to reduced hospital costs as a result. This chapter discusses posterior MIS decompression with descriptions of the procedures and outcomes.

17.2 Posterior Minimally Invasive Approaches for the Cervical Spine

Posterior decompressive procedures are fundamental tools in the surgical treatment of symptomatic cervical degenerative spine disease. ¹^, ²^, ³^, ⁴^, ⁵ Even as anterior cervical procedures have gained prominence, posterior cervical laminoforaminotomy still provides symptomatic relief in 92 to 97% of patients with radiculopathy from foraminal stenosis or lateral herniated disks. ³^, ⁶ Similarly, dorsal cervical decompression for cervical stenosis achieves neurologic improvement in 62.5 to 83% of myelopathic patients undergoing either laminectomy or laminoplasty. ⁴^, ⁷^, ⁸^, ⁹ Moreover, these operations avoid the complications related to anterior approaches to the cervical spine, namely, esophageal injury, vascular injury, recurrent laryngeal nerve paralysis, dysphagia, and accelerated degeneration of adjacent motion segments after fusion. ⁹^, ¹⁰^, ¹¹^, ¹²

Open dorsal approaches to the cervical spine require extensive subperiosteal stripping of the paraspinal musculature, leading to increased postoperative pain, spasm, and dysfunction and can lead to muscular ischemia, which in 18 to 60% of patients is persistently disabling. ⁴^, ¹⁰^, ¹³^, ¹⁵ Furthermore, preoperative loss of lordosis and long-segment decompressions increase the risk for postoperative sagittal plane deformity, ¹⁵^, ¹⁶^, ¹⁷^, ¹⁸^, ¹⁹ a complication that frequently prompts instrumented arthrodesis to be performed at the time of laminectomy. Using these extensive posterior fusion techniques increases operative risks, time, and blood loss; exacerbates early postoperative pain; and potentially contributes to adjacent-level degeneration.

The fundamental basis of minimal access techniques is to reduce approach-related morbidity by minimizing tissue disruption. The advent of the muscle-splitting tubular retractor system and the use of endoscopic technology or the operating room microscope have allowed for the application of MIS techniques to dorsal cervical decompressive procedures ¹⁴^, ¹⁵^, ²⁰^, ²¹^, ²²^, ²³^, ²⁴^, ²⁵^, ²⁶^, ²⁷^, ²⁸^, ²⁹^, ³⁰^, ³¹^, ³²^, ³³^, ³⁴^, ³⁵ and fixation. ³⁵^, ³⁶^, ³⁷^, ³⁸^, ³⁹

Between 1944 and 1947, Spurling, Scoville, and Frykholm were first to describe the open cervical foraminal decompression. ⁴⁰^, ⁴¹^, ⁴² In 1983 Williams reported the first microsurgical technique for dorsal cervical foraminotomy, ⁴³ and several minimally invasive dorsal cervical techniques were described subsequently. ²⁰^, ²¹^, ²²^, ²³^, ²⁴^, ²⁵^, ²⁶^, ²⁷^, ²⁸^, ²⁹^, ³⁰^, ³¹^, ³²^, ³³^, ³⁴^, ³⁵^, ³⁶^, ³⁷^, ³⁸^, ³⁹ To simplify description of all these techniques, we divide them into two main approaches: (1) the minimally invasive midline cervical approach and (2) the minimally invasive paramedian (transmuscular) cervical approach. An endoscope, microscope, or loupes and a headlight can be used with either approach. These approaches are used to perform MIS laminotomy, foraminotomy, diskectomy, laminectomy, and lateral mass fixation. ³⁵^, ³⁶^, ³⁷^, ³⁸^, ³⁹

17.3 Patient Selection

Operative indications for minimally invasive laminotomy, foraminotomy, or diskectomy are (1) unilateral single-root or multiple-root cervical radiculopathy from lateral disk herniations or foraminal stenosis (single-level or multilevel), without instability, significant kyphosis, or severe axial neck pain; (2) persistent or recurrent root symptoms after anterior cervical diskectomy and fusion; (3) cervical disk disease in patients for whom anterior approaches are relatively contraindicated (e.g., ventral neck infection, tracheostomy, prior irradiation); and (4) to avoid potential complications of the ventral approach and in cases where the anterior approach is less desirable (e.g., short neck or others). An anterior approach is generally most appropriate in the case of same-level bilateral radiculopathy, central disk herniation, uncinate spurs, significant kyphosis, and severe axial neck pain.

Most patients who are candidates for a noninstrumented, dorsal cervical decompression are also candidates for MIS posterior cervical decompression: myelopathy or myeloradiculopathy, and spinal cord compression from one to three adjacent cervical levels, with a lordotic cervical spine. Contraindications include loss of the normal cervical lordosis, severe ventral disease (disease that extends for more than three levels), and segmental instability. MIS lateral mass screw insertion technique can be used to treat segmental instability after decompression after facet dislocation or to augment previous ventral fusion techniques. ³⁵^, ³⁶^, ³⁸

17.4 Preoperative Preparation

Preoperative radiographic evaluation follows a detailed history and physical examination and should include magnetic resonance imaging or computed tomography myelogram, in addition to anteroposterior, lateral, and dynamic cervical radiographs. Electromyography (EMG) and nerve conduction studies may also assist in confirming the localization of radicular compression. Selective nerve root blocks can also be a useful additional therapeutic and diagnostic tool. All patients with pure radiculopathy who go on to surgery are patients for whom a trial of conservative therapy has failed; conservative measures include oral medications, physical therapy, and steroid injections. Cervical spondylotic myelopathy patients undergo a careful analysis of their disease progression, along with, radiographic studies, and comorbidities. All patients need careful counseling about the risks, benefits, and alternatives to surgery.

17.5 Operative Procedure

17.5.1 Operative Setup

General endotracheal anesthesia is induced with the patient on a standard electric operating table. A neurophysiologic monitoring array with capabilities for somatosensory evoked potentials, motor evoked potentials, and free-running EMG may be used. In cases of myelopathy, fiberoptic intubation may be elected, and evoked potentials are compared before and after positioning to identify positioning-related cord ischemia. Maintenance of normotension to avoid spinal cord hypoperfusion is best directed with continuous blood pressure measurements afforded by an arterial line. Measures to detect and treat air embolism, such as a precordial Doppler and a central line, are options but have not yet proven necessary. Given the small exposure, the risk of air embolism is low. A urinary catheter is generally not necessary for one- or two-level procedures. Routine perioperative antibiotics are administered. Use of relaxants is minimized after induction to allow for effective neurophysiologic monitoring.

Posterior cervical approaches can be performed with the patient in the prone or sitting position. In the prone position, the head is held with a Mayfield pin-holder or a well-padded horseshoe-shaped headrest with slight flexion. The operating table is tilted in a reverse Trendelenburg position to ensure that the cervical spine is parallel to the floor. We prefer the sitting position ( ▶ Fig. 17.1) because it confers the 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. The table is 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 semisitting position with the head flexed and the neck straight and perpendicular to the floor.

Fig. 17.1 Sitting position with C-arm in place.

17.5.2 Midline Approach

A 3-cm skin incision is made in the dorsal midline with the disk space centered on the incision. Larger incisions extending over several segments may be necessary for multilevel disease. The operative level(s) and entry point are confirmed on lateral fluoroscopy. The superficial fascia is incised in the midline to the level of the ligamentum nuchae. The ligamentum nuchae is incised just off the midline ipsilateral to the site of interest. Care should be taken to avoid penetration into the erector spinae muscles by staying along the margin of the bloodless deep fascia. After reaching the spinous processes of the site of interest, paraspinous muscles are dissected from the spinous processes, laminae, and facet joint using a monopolar cautery or subperiostal dissection with a Cobb. A self-retaining retractor is placed to reflect the paraspinous muscles from the interlaminar space of interest. The remaining steps are performed under microscopic magnification or using loupes and an endoscope.

17.5.3 Paramedian Approach

The operative level(s) and entry point are confirmed on lateral fluoroscopy with a K-wire. A 1.8-cm longitudinal incision is marked out approximately 1.5 cm off the midline on the operative side and injected with local anesthetic. For two-level procedures, the incision should be placed midway between the targeted levels. Once an optimal trajectory is established, dissection down to the fascia is performed with monopolar cautery (see ▶ Fig. 17.2), and then the fascia is incised using a scalpel or monopolar to accommodate the dilators. A Metz scissors is used to bluntly dissect to the facets to enable “force-free” insertion of the tissue dilators. The fascia is retracted, and the smallest dilator is placed through the posterior cervical musculature under fluoroscopic guidance and docked at the facet at the level of interest. A slightly lateral trajectory is advised to avoid the spinal canal and ensure contact with the lateral mass. Successive tubular muscle dilators are carefully and gently inserted, remembering that the axial forces that are routinely applied during muscle dilation in the lumbar spine are hazardous in the cervical spine. After dilation, the final tubular retractor is placed and secured over the junction of the lamina and the facet with a table-mounted flexible retractor arm; the dilators are removed ( ▶ Fig. 17.3). The following steps are performed under microscopic magnification or using loupes or an endoscope. The endoscope is inserted and attached to the tubular retractor ( ▶ Fig. 17.4). Monopolar cautery and pituitary rongeurs are used to clear the remaining soft tissue off the lateral mass and lamina of interest, taking care to start the dissection over solid bone laterally.