Anterior Cervical Corpectomy and Fusion/Instrumentation

Daniel G. Kang, MD

Ronald A. Lehman Jr, MD

K. Daniel Riew, MD

Dr. Lehman or an immediate family member serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons, the North American Spine Society, the Cervical Spine Research Society, and the Scoliosis Research Society. Dr. Riew or an immediate family member has received royalties from Biomet, Medtronic Sofamor Danek, and Osprey; has stock or stock options held in Amedica, Benvenue Medical, Expanding Orthopedics, NexGen, Osprey, Paradigm Spine, PSD, Spinal Kinetics, Spineology, and VertiFlex; has received research or institutional support from Medtronic Sofamor Danek and Cerapedics; and serves as a board member, owner, officer, or committee member of the Korean American Spine Society, the Cervical Spine Research Society, AOSpine, the North American Spine Society, and the Scoliosis Research Society. Neither Dr. Kang nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

PATIENT SELECTION

Indications

Anterior cervical corpectomy and fusion (ACCF) is most commonly performed for cervical spondylosis, with symptoms of cervical radiculopathy, myelopathy, or a combination of both. Cervical spondylosis describes a wide spectrum of degenerative changes in the cervical spine that involve the intervertebral disk, vertebral body, uncovertebral joint, and facet joint. Cervical radiculopathy is described as nerve root compression that causes radiating pain from the neck into the upper extremity. Cervical nerve root compression occurs most commonly by herniation of intervertebral disk material, but it is also associated with loss of foraminal height because of chronic disk degeneration as well as osteophytes and facet hypertrophy.¹ Indications for surgical management include severe or progressive neurologic deficit or significant pain that fails to respond to nonsurgical treatment.

Cervical spondylotic myelopathy occurs as a result of the degenerative process with aging, but it is also commonly associated with ossification of the posterior longitudinal ligament (OPLL), hypertrophy of the ligamentum flavum, or a congenitally narrowed cervical canal.² Other causes of cervical spinal cord compression include trauma, instability, tumor, infection, epidural abscess, and kyphotic deformity.³ Early surgical management is beneficial for most patients with severe or progressive myelopathy with concordant radiographic evidence of cord compression. For patients with nonprogressive mild to moderate myelopathy, however, no clearly established guidelines exist to dictate surgical management.⁴ In our practice, we recommend surgery for nonprogressive myelopathy when myelopathic symptoms and long-tract signs are present, in combination with a JOA (Japanese Orthopaedic Association) score of less than 13 points and concordant radiographic evidence of cord compression. In addition, any patient with a cord signal change on the magnetic resonance image is recommended for surgery. The results of surgical management are generally better in patients who undergo decompression early rather than late, as prolonged compression can result in irreversible histologic and physiologic changes within the spinal cord.⁵^,⁶ Patients with mild myelopathy are occasionally offered a trial of observation with collar immobilization and activity modification; however, nonsurgical management is generally not successful in reversing or permanently preventing the stepwise progression of myelopathy.⁵ The primary goal of ACCF is to decompress the spinal cord to prevent further neurologic deterioration and possibly reverse myelopathic symptoms. Secondary goals of ACCF include achieving successful fusion to stabilize abnormal motion segments to relieve spondylotic neck pain and correcting deformity, which may secondarily improve cord perfusion by decompressing obstructed spinal vessels.⁵

The major advantage of the anterior approach for cervical myelopathy and radiculopathy is the ability to directly decompress structures most commonly responsible for cord compression and nerve root impingement, including herniated disk material, osteophytes, and the posterior longitudinal ligament (PLL). In contrast to posterior approaches, anterior decompression can also indirectly relieve nerve root compression through reestablishing disk height and, subsequently, neuroforaminal height, as well as better correct kyphotic deformity and provide a fusion to address spondylotic neck pain.⁵ Several techniques are used for anterior cervical decompression and fusion, and the optimal technique continues to be debated. Corpectomy is considered over multilevel diskectomy in the patient who has two or three affected levels, developmental stenosis demonstrating an osseous anterior-posterior canal diameter of less than 13 mm, significant fixed cervical kyphosis,
large posterior osteophytes adjacent to the end plate, a free disk fragment that has migrated posterior to the vertebral body, or a significant component of spondylotic neck pain.⁵ The corpectomy procedure is more technically challenging, but it allows better decompression of the intervertebral level than does anterior cervical diskectomy and fusion. This is mainly a result of the improved access and visualization afforded by taking down the vertebral body at the intervening segment. Additionally, the bone graft/interbody spacer needs to fuse to only two surfaces, versus the four fusion surfaces required to obtain an arthrodesis in a two-level anterior cervical diskectomy and fusion. In patients who have only retrodiskal compression, we prefer to leave the posterior cortex of the corpectomy body intact. This improves the torsional stability of the construct and helps to prevent intrusion of the graft into the canal. For problems in three or more levels, if at all possible we try to perform a corpectomy of one level and diskectomies at the remaining levels to preserve stability, as a corpectomy-diskectomy is less likely to extrude a graft or collapse than is a two-level corpectomy.

Contraindications

Contraindications to ACCF are limited and include general contraindications to surgery, such as hemodynamic instability after trauma or multiple medical comorbidities that would preclude safe anesthetic induction. Other contraindications include tracheoesophageal trauma that would not allow safe anterior cervical exposure.³ Severe osteoporosis could also lead to progressive segmental kyphosis or graft subsidence, resulting in a failed fusion. A posterior approach is considered when posterior compression is a result of buckling of a hypertrophic ligamentum flavum or shingling of the laminae in a patient with hyperlordosis.⁵ A posterior decompression procedure is also considered when there are three or more affected levels in a patient without significant kyphotic deformity or neck pain.⁷^,⁸ We prefer to perform anterior surgery whenever possible; however, because the risk of infection is lower, it allows for more direct decompression, and there is less postoperative pain.

PREOPERATIVE IMAGING

Radiographic evaluation for patients with cervical spondylosis includes upright AP, lateral, and flexion-extension lateral plain radiographic views and, most typically, magnetic resonance scans. CT myelography may be necessary if MRI cannot be obtained or the images are difficult to interpret. Rarely, both MRI and CT myelography may be required.

Plain radiographs are useful in localizing pathologic levels of cord or nerve root compression, determining the degree of congenital cervical stenosis, assessing cervical sagittal alignment, and evaluating instability on flexion-extension lateral views.⁴ MRI and CT myelography can confirm spinal cord and nerve root compression. MRI is noninvasive and provides excellent evaluation of neural structures, soft tissues, and disk herniation, but it provides limited bony visualization.² It is critical to check the preoperative magnetic resonance scan for the presence of an anomalous vertebral artery. The artery may lie ventral to the vertebral foramen above C7, in which case it can be injured while the longus colli is elevated. Alternatively, the artery may weave a tortuous course through the vertebral body, in which case it can be injured during the corpectomy.

If a patient cannot undergo MRI for medical reasons (eg, cardiac pacemaker, aneurysm clips) or if metal from prior cervical spine instrumentation would preclude adequate visualization because of artifact, then CT myelography is considered. CT myelography provides outstanding resolution of bony structures, osteophytes, and OPLL, as well as neural anatomy of nerve root and spinal cord compression.⁴ Also, if high-quality MRI is performed but questions remain regarding bony anatomy, a noncontrast CT scan can be obtained to provide complementary information for surgical planning. We obtain a plain CT in select situations to determine (1) fusion assessment in patients with previous operations; (2) presence of severe facet arthrosis that may not have neural compression but may do better with a fusion for relief of axial pain; (3) the presence of OPLL or ossification of the ligamentum flavum, and the extent to which diffuse idiopathic skeletal hyperostosis may have autofused segments; and (4) the presence of autofused facets that can help to limit the number of levels requiring fusions. Evaluation of vascular structures, particularly the vertebral arteries, in cases of tumor involvement of the vertebral bodies or spinal cord may require preoperative angiography and embolization of a vascular tumor.³

PROCEDURE

Patient Positioning

The patient is positioned supine on the operating table, with the arms tucked to the sides. A small bump or roll is placed between the scapulae; this extends the neck slightly and drops the shoulders. If iliac crest autograft is to be used, a small bump is placed underneath the hip. If a fibular strut autograft is to be used, a thigh tourniquet is placed with a bump underneath the ipsilateral hip. We use a Jackson flat top operating table. If there is excessive bleeding during the case, the table can be tilted to 10° to 20° of reverse Trendelenburg, allowing venous drainage and reducing bleeding.⁹ We prefer to use intraoperative transcranial motor- and somatosensory-evoked potentials to monitor spinal cord activity. In cases of severe myelopathy, where evoked potentials may be unreliable or severe stenosis would compromise the spinal cord with neck extension, the anesthetic protocol includes awake, fiberoptic, or nasotracheal intubation. Additionally, our practice has evolved to use transient intravenous anesthesia to facilitate better motor-evoked potential readings. Additionally, 3-inch silk tape is used
to tape the head down to the table to limit rotation during surgery. Gardner-Wells tongs are applied to the head in cases of corpectomies of three or more levels (because Caspar pins are difficult to place for such lengths), with initial intraoperative traction of 15 lb of weight. Evoked potentials are again reviewed before proceeding. The application of Gardner-Wells tongs facilitates in-line traction and helps to stabilize the head and spine and control rotation during decompression and fusion. We tape the shoulders to the bottom of the operating table with 3-inch silk tape. Care is taken to prevent overpulling the shoulders because a traction brachial plexopathy can result. To avoid this, and to ensure that we can pull on the arms to obtain radiographic visualization of the lower levels, we place a looped Kerlix gauze bandage roll (Covidien) on the wrists and place the other end at the foot of the table to pull during radiographs. The patient is then prepared and draped in the usual manner.⁹

Special Instruments/Equipment/Implants

Graft

We prefer to use freeze-dried allograft fibula or ulna for most cases. An appropriately sized allograft is selected at the beginning of the case. We try to choose one that will maximally fill the corpectomy defect. An appropriately sized graft should leave only about 5 to 7 mm of lateral wall. The width of the vertebral body can be determined on the axial MRI or CT images. Occasionally, we choose a fresh-frozen graft for better healing.

Operating Microscope

We typically perform anterior cervical corpectomy using an operating microscope, although loupe magnification with a fiberoptic headlight may be used based on surgeon preference. We believe the operating microscope provides several advantages over loupe magnification. First, the magnification on the operating microscope can be changed easily during particular portions of the case, such as during corpectomy and decompression, when magnification is increased, or with graft placement and instrumentation, when magnification is decreased. Furthermore, the magnification of the microscope is more powerful than standard loupe magnification. The operating microscope also enhances lighting and visualization because it has a perfectly coaxial light source and allows operating room personnel to observe the progress of the surgical procedure.⁹ The operating microscope is especially helpful when a complication such as a dural tear is encountered because it allows the co-surgeon to provide meaningful assistance. The ability of the co-surgeon to assist on all other aspects of the case cannot be underestimated. With the use of loupes, only one surgeon can adequately look into the surgical wound.

The operating microscope is covered with a sterile microscope drape at the start of surgery. The microscope is then brought into the operating field after the disk space is localized with a lateral image. We prefer to use the operating microscope from the beginning of the deep exposure and will even close the wound with the use of microscope. This makes it possible to get a perfect closure and also allows trainees to practice suturing under the microscope, a skill that is required to close dural leaks. Modern microscopes have a long boom, allowing the head of the microscope to be brought in from the foot of the table on the side of the assisting surgeon. Once the microscope is in proper position, the covering of the eyepieces are torn off and the eyepieces are adjusted to accommodate eye width as well as refraction.⁹

Approach

We perform a Smith-Robinson anteromedial approach for exposure of the middle and lower cervical spine. We prefer a left-sided approach⁹; however, either a right- or left-sided approach to the anterior cervical spine may be selected based on surgeon preference, or the approach may be dictated by prior anterior cervical exposure. Anecdotally, some surgeons have suggested that right-sided approaches more commonly injure the recurrent laryngeal nerve (RLN) as a result of anatomic considerations. In a retrospective review, Beutler et al¹⁰ found no increased incidence of RLN injury when comparing right- and left-sided approaches. The authors reviewed only 173 right-sided and 155 left-sided cases, however, and reported a 2.7% RLN palsy rate. Such numbers are too underpowered to make conclusions about injury to a nonrecurrent laryngeal nerve, which occurs only on the right side and in only approximately 1% of cases.

In cases of revision anterior cervical exposure, preoperative evaluation with a direct laryngoscopy by an otolaryngologist is necessary to identify residual vocal cord paralysis.² If vocal cord paralysis is present, the approach is performed on the same side as the previous surgery. If no evidence of paralysis is present, however, the opposite side may be approached to reduce the need to dissect through previous scar tissue or adhesions.

Landmarks for Incision

Palpation of surface landmarks is useful in deciding incision location.² The hyoid bone is in the midline at the lower border of the mandible, approximately at the level of C3. The thyroid cartilage overlies approximately the C4-5 intervertebral disk space; it is the first large protuberance palpable inferior to the hyoid bone. The cricoid cartilage and carotid tubercle are at the level of C6.⁹ The level of the incision can also be approximated by examining a preoperative lateral image. The surgeon can check the radiographs to determine the location of the surgical level with respect to the distance between the angle of the mandible and the clavicle. This provides another rough estimation of where to make the incision.

Surgical Technique

The surgical procedure should be performed in a nearly identical, stepwise fashion each time. This makes it possible for the surgeon, assistant, and scrub nurse to learn the procedure quickly and improve efficiency each time the procedure is performed. Here we describe our current technique for doing a corpectomy. Innumerable variations are possible, and we continue to vary our technique nearly every year to refine it. Our current technique is certainly not likely to be the best. For the novice, however, it does help to memorize a step-by-step technique such as this one until enough experience is gained to allow for variations without compromising efficiency.

VIDEO 99.1 Cervical Corpectomy Part I: Exposure, Diskectomy, and Initial Corpectomy. Daniel G. Kang, MD; Ronald A. Lehman, Jr, MD; K. Daniel Riew, MD (19 min)

View Quicktime Video

Video 99.1

Superficial Exposure

For a single-level corpectomy, a 3- to 4-cm transverse incision is made along the Langer lines, beginning just past the midline and extending to the medial border of the sternocleidomastoid (SCM) muscle. For a multiple-level corpectomy, the skin incision is extended farther across the midline and to the lateral border of the SCM muscle. The steps of exposure are as follows:

1. The skin incision is marked with a fine-tip marker. Vertical lines are drawn every centimeter to serve as landmarks during closure so that the skin edges are brought back evenly. The skin is infiltrated with a local anesthetic with epinephrine using a 25-gauge needle as superficially as possible, immediately after the drapes are on the patient. This allows the anesthetic to take effect for at least 5 minutes while the rest of the equipment is being placed on the patient and decreases superficial bleeding. We usually call for a localizing radiograph at this point, as it takes several minutes for the radiology technician to arrive.

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