Anterior Cervical Discectomy and Corpectomy

Summary of Key Points

Anterior cervical discectomy provides rapid relief from radicular arm pain and halts progression of myelopathy.
Corpectomy is indicated for anterior spinal cord compression between the disc spaces.
Completeness of discectomy and corpectomy is based on intraoperative identification of the pedicles.
Subsequent spinal reconstruction involves implantation of autograft or allograft, usually contained in titanium or polyetheretherketone cages and stabilized with internal fixation.
Anterior plating increases fusion rates and can help reduce deformity.
Consideration should be given to supplemental posterior fixation or halo vest immobilization following two- and three- level corpectomies.

Acknowledgment

The senior author would like to express great debt and gratitude to Dr. Volker KH Sonntag for having the patience, guidance, skill, and mentorship necessary to impart such wonderful knowledge. Through this chapter we hope only in some small way to help perpetuate his far-reaching influence.

Anterior Cervical Pathologies

Surgical pathology of the anterior cervical spine can be anatomically categorized into that involving the disc or that involving the vertebral body. However, it is perhaps more intuitive to characterize pathology in epidemiological terms. Cervical spondylosis is by far the most common pathology encountered by the spinal surgeon. Magnetic resonance imaging studies of asymptomatic patients show that degenerative changes increase linearly with age. More than 87% of people over 60 years of age show at least one level of advanced disease. Degeneration is largely focused at the disc space, resulting in foraminal stenosis, spinal canal stenosis, cervical kyphosis, and segmental spondylolisthesis as a result of progressive disc space collapse, disc herniation, osteophyte formation, and ligamentous and facet hypertrophy.

In an aging population with emerging comorbidities the frequency of infection is rising. A retrospective epidemiological analysis from Spain indicated that symptomatic presentations of vertebral osteomyelitis increased 494% between 1985 and 2011. Age-associated diabetes and renal failure, along with intravenous drug abuse, comprise the primary risk factors for discitis and subsequent osteomyelitis. Patients older than 75 years with pyogenic osteomyelitis have a higher prevalence of neoplasia and chronic inflammatory diseases. The intervertebral disc has no blood supply, and subsequently poor immunological surveillance; bacterial infections invariably begin in the disc, spreading radially to erode through end plates into vertebral bodies, also producing epidural collections of pus or granulation tissue. Fungal infections such as tuberculosis can begin in the vertebral body and spread to the disc space secondarily. The preponderance of infectious pathology is located anteriorly because of the location of the intervertebral discs.

Tumors of the cervical spine can be of primary or secondary origin. Both tend to affect the anterior cervical spine most frequently. In contrast to the intervertebral disc, the rich vascular supply of the vertebral body makes it a prime target for metastatic disease. By nature of its larger volume compared with the posterior elements, the anterior spine is also more commonly affected by primary bone tumors.

Trauma causes failure of the anterior spine through translation affecting the disc and surrounding ligaments, or through loading causing the vertebral body to fail. Even unilateral or bilateral facet fracture/dislocations affect the anterior cervical spine through the disc disruption.

The two most widely accepted clinical indications for anterior approaches to the cervical spine are myelopathy and medically-refractory radiculopathy. Whereas structural compromise from discitis/osteomyelitis and trauma can also necessitate operative intervention, axial neck pain and cervicogenic headache with or without kyphotic deformity are not widely accepted indications for surgery. In general, spinal column pathology anterior to the spinal cord should be treated by anterior spinal surgery. This is especially true when the pathology is focal (i.e., one to two segments) or in the setting of kyphosis. For these reasons, familiarity with the surgical approach and limitations to anterior single- or multilevel constructs is a requisite skill set for the spinal surgeon.

Approach and Limitations

Preoperative Planning

For patients in whom cervical stenosis is either expected or confirmed, full range of motion in the neck should be examined preoperatively, looking for symptoms of transient cord compression (Lhermitte sign). The presence of these symptoms must appropriately limit positioning to a more neutral alignment when the patient is under general anesthesia. Consider obtaining intraoperative motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs) immediately after induction (baseline) and again after positioning in these patients.

In the setting of prior anterior neck dissection (including nonspinal causes such as thyroidectomy, etc.) direct laryngoscopy should be obtained preoperatively to verify function in both vocal cords, thereby attesting to normal recurrent laryngeal nerve function. In the setting of a known recurrent laryngeal nerve palsy, anterior neck dissection should be performed on the side of the palsy. Preoperative direct laryngoscopy is not necessary if the surgeon elects to operate on the same side as previous surgery.

Intraoperative electrophysiological monitoring (IOM) is an option when planning anterior cervical surgery. SSEPs, MEPs, and free-running electromyography activity can be recorded and may indicate damage to a nerve root or the spinal cord. However, the opportunity to reverse this damage based on IOM feedback has only been reported in thoracolumbar deformity cases. False positive and false negative recordings are not uncommon; surgeons should always be prepared to exercise their experience and judgment in interpreting IOM results.

Positioning

For cervical discectomy and corpectomy the patient is positioned supine on a radiolucent bed. All invasive lines and monitoring should be secured with tape to ensure safe movement of fluoroscopic equipment throughout the surgery. The endotracheal tube is directed away from the surgical side of the neck (i.e., toward the midline forehead or opposite side) so that it does not interfere with the operative site. Access to the disc space is enhanced by accentuating cervical lordosis. This is achieved by placing a bolster under the shoulders and a roll behind the neck. The patient’s head rests in a low-profile gel donut. This positioning is in contrast to the neutral alignment recommended for disc arthroplasty. Neck extension should also be limited in cases of severe central canal stenosis, thereby minimizing the risk of cord injury.

Placing a bolster under the upper thoracic spine to produce lordosis also allows the shoulders to fall toward the table, reducing the distance from the sternum and clavicles to the spine. Taping the shoulders to the end of the surgical table will pull the clavicles and sternum toward the feet, increasing caudal spinal exposure. The shoulders should be taped in a lateral configuration from the trapezius over the acromioclavicular joint and along the lateral humerus ( Fig. 110.1 ). Taping the shoulders anteriorly over the biceps or chest will pull the shoulders forward, interfering with fluoroscopy and deepening the access corridor to the spine.

Fig. 110.1, The shoulders should be taped down laterally along the trapezius, acromioclavicular joint, and lateral humerus with 3-in wide tape affixed to the inferior edge of the operating table. This will optimize radiographic visualization of the lower cervical segments and help minimize the depth of the surgical corridor. In this photograph bolsters can be appreciated behind the upper thoracic spine. These are placed to facilitate lordotic positioning of the cervical spine. An arm sled can also be seen holding the patient’s arm against the body. Green arrows indicate direction of shoulder retraction by tape.

Surface landmarks are valuable when planning the incision. In the ideal neck, the superior thyroid cartilage is in the region of C3‒C4, the inferior thyroid cartilage is in the vicinity of C4‒C5 and C5‒C6, and C6‒C7 is located two fingerbreadths above the clavicle ( Fig. 110.2 ). Although traditional neurosurgical teaching involves a right-sided neck dissection, left-sided approaches historically employed by orthopedic spine surgeons are identical. However, anatomical nuances specific to each are encountered in low dissections, as described later.

Fig. 110.2, Typical relationship of disc spaces to the thyroid cartilage. The superior border of the thyroid cartilage can be used to plan an exposure of C3‒C4, whereas an incision based in a skin crease near the inferior border will allow access to C4‒C5 and C5‒C6. C6‒C7 is about 2 fingerbreadths above the clavicle. Note that access to the C7‒T1 disc space is often achievable just above the clavicle, but the direction of the end plates can make deep disc removal difficult.

Once the incision level is mapped against surface anatomy, a transverse incision is typically planned in a skin crease, within a centimeter or two of the appropriate surface landmarks. Transverse incisions in a skin crease yield much better cosmetic results compared with vertical incisions along the anterior border of the sternocleidomastoid (SCM), yet they still allow for exposure from C2 to T2. The incision is marked from the midline neck to the anterior border of sternocleidomastoid. For multilevel surgeries the incision is extended 2 to 3 cm across the midline and a similar distance beyond the border of the SCM.

Complication Avoidance

Thick, short necks provide two challenges: it is (1) more difficult to identify normal anatomy of the surgical corridor; and (2) more difficult to achieve adequate exposure. Make sure the neck is extended and the shoulders are taped down properly. Consider rotating the head 45 degrees away from the incision. A bigger incision and more extensive dissection are required. Never proceed unless the anterior border of SCM and the medial border of the carotid artery are sequentially identified; otherwise, the risk of esophageal perforation is high.

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