20 Anterior Cervical Discectomy, Fusion, and Instrumentation

Minimally invasive spine surgery is becoming increasingly popular as a means of treating spine pathology. The anterior cervical approach to the spine can be performed in a muscle-sparing manner via fascial planes to reduce approach-related morbidity. The anatomy of the approach allows the surgeon to perform this approach via a traditional technique and still preserve the muscle anatomy while having the benefits of direct visualization and reduced risk to anterior spinal structures. Autograft remains the standard of care for anterior cervical discectomy and fusion; however, patient dissatisfaction with iliac crest graft site morbidity remains a significant drawback of this graft option.¹ Use of instruments developed to collect local bone graft (i.e., BoneBac Press, Thompson MIS) can eliminate graft site morbidity while using autograft.

20.2 Indications

Typical indications for anterior cervical discectomy include patients with myelopathy or bilateral radicular symptoms attributed to a central disc herniation, large lateralized disc herniations, large bone osteophytes leading to radiculopathy, and collapsed disc causing bilateral foraminal stenosis and progressive kyphosis. This approach allows for direct decompression of the spinal cord while allowing for restoration of disc and foraminal height and normal sagittal lordosis. When the level of neck pain can be identified, this approach provides for excellent fusion since the graft is placed under compression, which promotes arthrodesis.

20.3 Preoperative Planning

After general anesthesia induction, the patient is placed in the supine position on the operating table. We prefer using a Jackson flat table that allows for the C-arm fluoroscopic unit to be pushed down toward the feet and out of the way of the surgeon. A small shoulder roll is placed under the shoulder if needed to aid in slight extension or neutral position of the neck. Care is taken to confirm that the neck is not placed in an overextended position. In those patients with significant myelopathy due to cord compression, fiberoptic intubation is performed after which the patient is asked to move all four extremities before induction. Next, the fluoroscope is set in place for a lateral image of the cervical spine. This image is used to identify the target disc space. At times, gentle caudal retraction of the shoulders by pulling the hands toward the feet or by taping the shoulders down is necessary for adequate cervical visualization in large or more muscular individuals. We have found it helpful to place a Kerlex loosely around each wrist. The arms can then be pulled down toward the feet during fluoroscopic imaging to view levels below C5 especially in patients with large shoulders to help properly identify the level of interest. The base of the fluoroscopic unit should be placed on the side opposite the surgeon so as not to encumber access to the spine. However, using a Jackson table allows for the fluoroscopic unit to be moved toward the patient’s feet and away from the operative field.

20.4 Surgical Instrumentation

A variety of surgical instrumentation is available for the anterior cervical approach. More recently, zero profile implants have allowed for interbody implant to be secured within the disc space without the need for an anterior cervical plate. The advantage may potentially be less dysphagia as there is not a plate overlying the cervical vertebrae and under the esophagus ( Fig. 20.1). Polyetheretherketone (PEEK) cages allow for autograft from the surgical bed to be used and have the benefit of X-ray visualization of fusion mass once it occurs. Expandable cage technology has facilitated reconstruction after vertebrectomy.

20.5 Surgical Technique

Cloward² and Robinson and Smith³ first described anterior surgical approaches in the 1950s as a method of neural decompression. Following discectomy, Cloward directly removed compressive structures and followed with fusion using a dowel-shaped graft.² Robinson and Smith³ fused the adjoining vertebrae using a horseshoe graft harvested from the iliac crest (IC), but left decompression to occur secondarily. In 1960, Bailey and Badgley,⁴ who had performed the first anterior cervical fusion in 1952, described a fusion technique for patients with neoplasm and instability involving on-lay strut grafts, a concept now utilized following corpectomy.⁵

Fig. 20.1 (a) Lateral and (b) AP X-ray radiographs showing zero profile implants used to perform C4–C5 and C5–C6 anterior cervical discectomy fusion and instrumentation.

The neck is prepped and draped in normal surgical fashion. A transverse skin incision is made lateral to the midline in the upper neck crease to approach the C2–C3 to C4–C5 levels and in the lower neck crease to approach the C5–C6 to C7–T1 levels. The side of the incision is made per preference of the surgeons. Many right-handed surgeons make the incision on the right side of the neck to facilitate the approach and surgery. After the skin incision is made, a careful subcutaneous incision/dissection is performed exposing the platysma muscle and the superficial fascia. The platysma muscle is then opened 1.5 cm longitudinally or can be cut with Bovey cautery and reapproximated at the end of the case with interrupted absorbable sutures. The medial border of the sternocleidomastoid muscle is identified and the fascial plane followed medial to the sternocleidomastoid muscle in the areolar plane. The external jugular vein can be dissected laterally off the sternocleidomastoid muscle and pushed medially. A Weitlander retractor is used to hold open the skin. Holding the retractor up allows for easier visualization of the areolar plane between the muscles and facilitates the dissection. With an index finger or Metzenbaum scissor, dissection via fascial planes of the anterior cervical region is done in such a way that the neurovascular (carotid artery) bundle is identified by tactile feel and retracted laterally while the esophagus and trachea remain medial ( Fig. 20.2).

The anterior vertebral body of the cervical spine is palpated. Kittner dissector can be used to gentle push the soft tissue to expose the anterior vertebral body and disc space. The longus colli muscle is dissected off the vertebral body at the level of the disc pathology using an insulated Bovey cautery tip. A 90-degree bent spinal needle, which prevents overpenetration of the disc space, is placed in the disc space and lateral fluoroscopic image taken to identify the disc space level. Distractor pins are placed in the appropriate vertebrae adjacent to the disc space of interest and retractors are placed medial to the longus colli muscles bilaterally. We prefer to use the thinnest toothed blades of the Trimline cervical retractor (Medtronic) as this can reduce retraction-related morbidity. The blades are positioned directly lateral to the disc space of interest. Because this region is less muscular than the posterior cervical and lumbar regions, the retractors can be easily moved, potentially resulting in retractor displacement relative to the disc space that is being operated on. For this reason, fluoroscopic imaging is used to verify the positioning of the retractor and distractor posts once in place( Fig. 20.3).

An annulotomy is made in the disc, and the disc is removed in a piecemeal fashion with pituitary rongeurs, curettes, and drill. A long, tapered drill is then used to remove osteophytes. The posterior longitudinal ligament can be removed after adequate discectomy to expose the dural and assure adequate distraction of the disc space. The posterior longitudinal ligament is removed starting laterally using an up-going microcurette to detach the ligament laterally. Next, a number 1 or 2 Kerrison punch is used to further remove the ligament and posterior osteophytes. The decompression continues to completely remove the disc herniation, posterior longitudinal ligament, and bone osteophytes ( Fig. 20.3).

After adequate decompression is achieved, a trial is used to identify the proper implant size. The implant can then be filled with bone graft material, typically autologous bone graft harvested from the surgical site using the BoneBac Press (Thompson MIS) (see Fig. 20.3). This bone can be mixed with bone graft extenders if needed and completely eliminate the need for IC harvest and its associated morbidity. With the implant in place, distractor pins are removed to allow for implant and graft compression. Distractor pin bone holes are filled with bone wax to prevent any bone bleeding. We prefer zero profile cages. These cages are easier to implant and secure to adjacent vertebrae while potentially helping to reduce the incidence of plate-induced dysphagia (see Fig. 20.1).

20.5.1 Closure

With complete hemostasis assured, the retractor blades are removed. The platysma muscle is reapproximated with 2–0 interrupted Vicryl suture. A subcutaneous suture is applied and the skin closed with either skin glue or Steri-Strips. Clean dressing is applied. At times, a drain is placed for multilevel approaches or cervical corpectomy and removed the following morning or shortly after.

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