Anterior Approach to the Cervical Spine

CHAPTER 43
Anterior Approach to the Cervical Spine

Discectomy, Fusion, and Vertebrectomy

Serena S. Hu

Indications

1. Patients with radiculopathy, pain, numbness or weakness in a dermatomal distribution, who require anterior discectomy and fusion; symptoms should correlate with the anatomic studies.

2. Vertebral corpectomy (i.e., a burst fracture with canal compromise, infection or tumor) (Fig. 43–6A)

3. Patients with cervical spondylosis who also have myelopathy, secondary to posterior osteophytes, or ossification of the posterior longitudinal ligament (OPLL); these patients may require anterior decompression via multiple level discectomies and fusion or corpectomy(ies).

4. In general, the standard anterior approach can be used to reach pathology from C4 to C7, although occasionally C3 or T1 can be reached in patients with long thin necks. Because of the mandible and collarbone, it is difficult to gain full anterior access to the ends of the exposure. Consequently, screw placement or other surgery at the incision ends can be difficult if not impossible.

Contraindications

1. In patients with greater than three levels of vertebral involvement, with adequate cervical lordosis, extensive OPLL is considered a relative contraindication. In these patients consider a posterior approach and laminaplasty.

Preoperative Preparation

1. Determine how many levels must be addressed surgically. Some surgeons feel that a partial vertebrectomy should be performed if multiple levels are involved. This allows a single bone graft to be placed in the trough, thereby requiring only two bony surfaces to heal to the host bone rather than the 4 or 6 that are needed if separate grafts are placed at each level. Others feel that with anterior plates, the fusion rate is acceptable even with three levels of bone graft.

2. Determine whether discectomies or corpectomies should be performed.

3. Determine if instrumentation is indicated. If so, the levels and construct to be utilized should be planned prior to surgery.

Special Instruments, Position, and Anesthesia

1. The surgery is performed under general anesthesia.

2. Either a left- or right-sided approach can be utilized. The left-sided approach is preferred by many surgeons because the recurrent laryngeal nerve has a more predictable distal course on the neck’s left side. Conversely, others prefer the right-sided approach because it is technically easier for a right-handed surgeon to work on the patient’s right side.

3. The endotracheal tube should be taped opposite to the side of the approach.

4. The patient is positioned with a small folded towel placed between the shoulder blades to allow the shoulders to fall back.

5. Consider stabilizing the patient’s head on a horseshoe (Mayfield) headrest in light (5 to 15 pounds) head halter traction. If desired, additional traction can be applied during bone graft placement.

6. Pull the patient’s shoulders distally and tape them to the end of the table to facilitate adequate X-ray localization. It can be difficult to balance the degree of shoulder traction needed to afford adequate X-ray visualization with the possibility of a traction injury to the brachial plexus.

7. The patient’s anterior iliac crest can be elevated slightly on a sandbag or folded towel.

Tips and Pearls

1. One or two disc levels can be easily reached through a transverse incision; for greater numbers of levels, a longitudinal incision along the anterior aspect of the sternocleidomastoid muscle can be used.

2. Many patients have posterior osteophytes that encroach on the spinal canal. Some surgeons feel that after a fusion, these osteophytes will resorb over time; conversely others feel that osteophyte removal results in faster relief of symptoms. To remove osteophytes, they can be thinned with a high-speed burr and then the remaining cortical edge hooked and removed piecemeal with a small microcurette.

3. Graft measurement includes both the height and depth of the graft. Generally grafts for cervical discectomies are 6 to 7 mm in height and 1.5 cm in depth. In general, the minimum graft height for adequate compressive strength and appropriate neural foramen enlargement is 5 mm.

4. If a vertebrectomy has been performed, the graft harvest should take into account the additional length needed to key in the ends of the graft for maximum stability (see Fig. 43–5B). If greater than two levels of vertebra are removed, the iliac crest may not be of adequate length and fibula graft may be preferable.

5. When multiple levels of discectomy are performed, or if corpectomy has been performed for fracture or myelopathy, anterior plate fixation may be used for additional stability. While bicortical purchase is generally optimal for plate stability, the neurologic risk associated with it is not insignificant. Thus, most modern anterior cervical plate systems utilize unicortical purchase and lock the screws to the plate to prevent the screws from backing out. Halo fixation is also an alternative, although not as rigid a construct.

6. For patients with significant pre-existing neurologic deficits, particularly myelopathy, some surgeons prefer to use spinal cord monitoring.

7. Dural injury is more common with significant OPLL as the dura may be attenuated or adherent.

8. Deteriorating neurologic function needs to be investigated for cause, and oftentimes treated with steroids. MRI or CT scan may demonstrate hematoma or bony encroachment and should be promptly addressed.

What To Avoid

1. Attempt to avoid injury to the spinal cord, nerve roots or dura. Be especially wary of instrument penetration secondary to inadvertent deep placement (especially during posterior osteophyte removal), excessive depth of bone graft placement, or over distraction.

2. Protect the thyroid gland, trachea and esophagus by retracting the strap muscles medially. In particular, esophageal perforation can lead to abscess, fistula or mediastinal involvement.

3. Avoid injury to the sympathetic chain, which can result in Horner’s syndrome. The sympathetic chain lies on the anterior aspect of the longus colli. Damage can be minimized by carefully dividing the longus colli in the midline and using the bipolar cautery rather than bovie cautery when possible.

4. Attempt to minimize airway problems particularly during prolonged procedures and in patients with cervical spinal cord injury. In these cases, consider prolonged intubation (2 to 3 days) to permit pharyngeal edema to decrease. Remember hoarseness may occur secondary to edema or retraction but rarely occurs if the recurrent laryngeal nerve is injured.