Anterior Cervical Corpectomy

Indications

Anterior cervical corpectomy and fusion (ACCF) is commonly performed to treat cervical spondylosis, cervical radiculopathy, or both.  Cervical spondylotic myelopathy (CSM) is a syndrome describing a wide spectrum of degenerative changes within the cervical motion segments that ultimately result in spinal cord compression at one or more levels.  In contrast, cervical radiculopathy describes a process in which cervical nerve roots are compressed, resulting in radiating pain from the neck into the upper extremity. Nerve root compression occurs most commonly from herniation of intervertebral disc material, but can also occur due to a decrease in foraminal height from chronic disc degeneration, osteophytes and facet hypertrophy.¹ Indications for operative management for cervical radiculopathy include severe or progressive neurologic deficit or significant pain that fails to respond to non-surgical treatment for more than 6 weeks.

Patients with CSM present with a variety of complaints, including loss of dexterity and fine motor coordination in the upper extremities and disturbances with balance and gait.  Objective findings include:

• Exaggerated deep tendon reflexes
• Clonus
• Spasticity
• Motor weakness
• Presence of pathologic reflexes

The pathophysiology of CSM is due to a variety of lesions in numerous anatomic locations that result in spinal cord compression.  Degenerative changes in structures anterior to the spinal cord, such as herniated disc material, osteophytic bone spurs, or an ossified posterior longitudinal ligament (OPLL), typically contribute to the development of CSM.  Other causes of CSM include ligamentum flavum hypertrophy or buckling, a congenitally narrowed cervical canal, facet joint cyst, and, less commonly, tumor or infection. 

Early operative management is typically indicated for severe or progressive myelopathy with concordant radiographic evidence of cord compression in order to halt the natural history of the disease process.  Unfortunately, there are no clear-cut guidelines dictating operative management for patients with non-progressive mild to moderate myelopathy.²  In our practice, which has also been described by Wada et al, we recommend surgery for mild to moderate myelopathy when long tract signs are present, in combination with a Japanese Orthopaedic Associated (JOA) score of <13 and evidence of spinal cord compression on imaging studies.³ 

The primary goal of operative management, whether an anterior or posterior approach, is to expand the spinal canal to prevent further neurologic compromise and to potentially reverse myelopathic symptoms. Additional goals specific to ACCF include the ability to achieve fusion to (1) stabilize abnormal segmental mobility, (2) relieve spondylotic neck pain, and (3) correct spinal deformity, which may secondarily improve cord perfusion by decompressing obstructed spinal vessels.⁴

An anterior approach is advantageous for management of CSM and cervical radiculopathy because the pathoanatomy resulting in cord compression typically occurs anterior to the cord, thus allowing direct decompression of the dura and removal of offending agents.²  The anterior decompression can also indirectly relieve nerve root compression through re-establishing disc height and neuroforaminal height; it also improves the ability to correct kyphotic deformity. 

There are several techniques for anterior decompression and fusion, and the optimal technique continues to be debated.  Corpectomy can be chosen over a multilevel discectomy for patients with:

• Two or three affected levels
• Developmental stenosis demonstrating an osseous antero-posterior canal diameter <13mm
• A large posterior osteophyte adjacent to the end plate
• A free disc fragment that has migrated posterior to the vertebral body
• Significant spondylotic neck pain⁴

Preoperative Planning

For patients with cervical spondylosis, preoperative imaging includes anteroposterior (AP), lateral, and flexion-extension views of the cervical spine, as well as magnetic resonance imaging (MRI), computed tomographic (CT) myelogram, or both. The lateral view is important as it demonstrates the degree of disk narrowing and size of the osteophytes and spinal canal, as well as sagittal alignment.²  Magnetic resonance imaging has the ability to assess the extent of pathology resulting from changes to adjacent soft tissues, along with the degree of cord compression.²  If a patient is unable to undergo MRI for medical reasons (ie, cardiac pacemaker, aneurysm clips), then a CT myelogram may be obtained. Although it has the disadvantage of being an invasive procedure, CT myelogram provides remarkable resolution of bony structures, OPLL, and neural anatomy.

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, which extends the neck slightly and drops the shoulders.  We use the OSI table with Jackson flat top (Mizuho OSI, Union City, CA), placing the head of the table on the top rung and the bottom of the table on the bottom rung. This puts the table into approximately 10 to 20 degrees of reverse Trendelenburg, allowing venous drainage and reducing bleeding during surgery.⁵

Intraoperative transcranial motor and somatosensory evoked potentials (MEP, SSEP) are used to monitor spinal cord activity, and are placed immediately following anesthetic induction. 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, fiber-optic or nasotracheal intubation. Additionally, our practice has evolved and transient intravenous anesthesia (TIVA) is utilized to facilitate better MEP readings. 

Three-inch-wide 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 surgeries at three or more levels, with initial intraoperative traction of 15 pounds; evoked potentials are again reviewed before proceeding. The application of Gardner-Wells tongs facilitates in-line traction, helps to stabilize the head and spine and control rotation during decompression and fusion.

We also tape the shoulders to the bottom of the bed with the three-inch-wide silk tape. This facilitates traction on the cervical spine and depresses the shoulders, improving fluoroscopic visualization of the lower cervical levels. Initial fluoroscopic images are obtained to ensure appropriate positioning for intraoperative antero-posterior and lateral fluoroscopic images. The patient is then prepped and draped in the usual manner.⁵

Approach

We use a Smith-Robinson antero-medial approach for exposure of the middle and lower cervical spine, and prefer a left-sided approach.⁵  Some surgeons have suggested that right-sided approaches more commonly injure the recurrent laryngeal nerve (RLN) due to anatomic considerations.  However Beutler et al, in a large retrospective review, did not find an increased incidence of RLN injury when comparing right- and left-sided approaches.⁶

In cases of revision anterior cervical exposure, preoperative evaluation with a direct laryngoscopy by an otolaryngologist is necessary to identify residual vocal cord paralysis.⁷  If vocal cord paralysis is present, the approach is carried out on the same side as the previous surgery.  However, if there is no evidence of paralysis, the opposite side may be approached to reduce the need to dissect through previous scar tissue or adhesions.

Palpation of surface landmarks is useful in deciding incision location.⁷  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-C5 intervertebral disc space, and is the first large protuberance palpable inferior to the hyoid bone.  The cricoid cartilage and carotid tubercle are at the level of C6.⁵

Technique

For a single-level corpectomy, a 3- to 4-cm transverse incision is made, beginning at midline and extending to the medial border of the sternocleidomastoid (SCM) muscle.  For a multiple-level corpectomy, the skin incision is extended across the midline to the lateral border of the SCM.  The most common error is making the incision too caudad; the surgeon must remember the exposure can more easily be increased caudally than cranially.⁸ 

After the skin is incised, sharp dissection is continued through subcutaneous tissue, and the platysma muscle is identified and incised using monopolar cautery in line with the skin incision.  A plane is developed deep to the platysma with blunt dissection to create subplatysmal pouches, which allows for the exposure of up to six levels through the single transverse skin incision.  Retraction of the divided muscle exposes the SCM muscle laterally and the sternohyoid and sternothyroid muscles medially. 

The carotid pulse should be palpated deep to the SCM, delineating the location of the carotid sheath laterally, and the trachea and esophagus are palpated medially.  Blunt dissection is performed through this interval posteriorly towards the midline to the prevertebral fascia and longus colli muscle.  The omohyoid, deep to the SCM, may be divided if necessary to improve exposure; however, the SCM muscle fascia should not be violated to reduce bleeding and keep the plane of dissection out of the carotid sheath.^7,8  No efforts are made to specifically identify the recurrent laryngeal nerve.⁵

Once the prevertebral fascia and longus colli muscle are reached, the anterior vertebral bodies are easily identified.  The prevertebral fascia is divided longitudinally and swept laterally to expose the longus colli muscle, anterior longitudinal ligament, intervertebral disc, and vertebral body.  The predicted disc space is then marked using a tonsil clamp, and a lateral fluoroscopic image is obtained to verify the correct level.  After the level is confirmed, the medial borders of the longus colli muscle are elevated using monopolar cautery in full-thickness flaps, and care is taken to remain under the longus colli muscle because superficial, lateral dissection may injure the sympathetic plexus. 

The longus colli muscle is then subperiosteally elevated off the anterior vertebral body and disc space using a monopolar cautery, and continued laterally until the vertebral body begins to curve posteriorly and the uncovertrebral joints are identified.⁷  Further dissection laterally, particularly at the disc spaces, endangers the vertebral arteries, but can be safely carried out by staying on or just superficial to the level of the costalprocess.⁸ 

Next, the medio-lateral smooth-tipped retractors are placed under the developed longus colli muscle flaps; the use of sharp-toothed retractors is avoided to prevent perforation of the esophagus medially and the carotid sheath laterally.⁸  Once adequate exposure has been obtained, we routinely request the anesthesia team to deflate the endotracheal tube to a pressure just above air leak to reduce compression of the viscera.

Exposure of the C2 and C3 levels should be performed with caution as the hypoglossal and superior laryngeal nerves may cross the plane of dissection; they should be gently retracted along with the digastrics and stylohyoid muscles. The superior thyroid artery and vein are encountered at the C6 and C7 levels, and in most cases, can be gently retracted to obtain adequate exposure.

After satisfactory deep exposure is obtained, we again verify the correct levels using a lateral fluoroscopic image, and the operating microscope is brought into the field. Caspar pins are placed into the vertebral bodies above and below the level to be removed.  A left-sided distractor is placed over the Caspar pins and traction is placed across those discs.  For a single-level corpectomy, the discs above and below the vertebral body are excised.  Intervertebral disc excision then proceeds, and anterior osteophyes are first removed with a Leksell rongeur to improve visualization of the disc space.  This is followed by an annulotomy using a #15 blade, followed by removal of disc material with a curette and pituitary rongeur. 

It is imperative to laterally dissect out to the costal processes and visualize the lateral aspect of the uncinate, as well as palpate along the lateral border of the uncinate using a penfield #4. The uncovertebral joints serve as the most reliable reference to the lateral borders of the vertebral body, and provide a pathway for decompression.⁵  Lateral vertebral osteophytes can easily be mistaken for the lateral vertebral body, causing the surgeon to over aggressively remove bone and endanger the vertebral artery.  

Following removal of the anterior annulus and disc material, a high-speed carbide burr is utilized to remove the remainder of the posterior annulus and thin out the posterior longitudinal ligament (PLL).  It is important to maintain the integrity of the PLL to provide a margin of safety between the posterior osteophytes and the dura.  We prefer the use of an acorn-shaped burr that is side-cutting.  This allows the surgeon to place the tip of the burr on the PLL and burr off the posterior osteophytes in a safe, efficient manner.

Once the PLL is appropriately thinned and the osteophytes removed, we begin preparing for the corpectomy.  By decompressing to the PLL, one can judge the true depth of the corpectomy.  The burr is then used to take the endplate off the cephalad and caudal aspects of the vertebral body to allow for easier use of the large Leksell rongeur.  We then create two vertical troughs with the burr on either side of the vertebral body to delineate the width of the corpectomy.  A large rongeur is used to “bite” the vertebral body.  At this time, there may be significant bleeding from the nutrient vessel along the posterior cortex of the vertebral body.  It is imperative to continue with the corpectomy and not stop to obtain hemostasis.  All bone that is obtained is saved for graft/fusion purposes. 

After the posterior margin of the vertebral body has been reached, a high-speed carbide burr is used to carefully thin the posterior wall of the vertebral body until it is a thin cortical shell.  This cortex is then thinned until it “floats” ventrally from the dura.  The remaining layer of bone is removed to expose the PLL; this is done with a small, angled curette or Kerrison rongeur, using a lifting motion aimed away from the dura.⁸ For a multiple-level corpectomy, each vertebral level is sequentially decompressed down to the thin posterior cortical shell. Final removal of the remaining cortical shell and exposure of the PLL is performed at the completion of vertebral body removal to allow optimal exposure and visualization. When the corpectomy is completed, the only visible structure posteriorly should be the PLL.

We then create a rent in the PLL at the intervertebral level, and incise it laterally with a 1 mm Kerrison rongeur.  This is carried out to the uncovertebral joint, and the uncinate is thinned or resected on the side of radiculopathy (if present).  Any extruded disc fragments are identified between the fibers of the PLL and removed using a rongeur.  A small nerve hook may be passed posterolaterally through the neural foramen. Any additional disc fragments or osteophytes causing compression are removed under direct visualization using a small, angled curette, a Kerrison rongeur, or with a high-speed carbide tipped burr.⁷ Ossification of the PLL may necessitate removal of the PLL; however, the dura may be adherent, and a small nerve hook is frequently used to help retract the OPLL away from the spinal cord while the calcified ligament is removed with a small, angle curette or Kerrison rongeur.⁸

Following completion of corpectomy and decompression, the size of the required allograft or corpectomy cage is measured using microsurgical calipers.  The graft or cage is gently tamped into place, positioned, and countersunk into the concavity of the lower vertebra, and Caspar pin distraction is released.  Any additional autogenous cancellous bone obtained during the corpectomy can be packed lateral to the strut graft at the uncinates.⁵  Graft position is verified with orthogonal fluoroscopic images.

The shortest possible plate that spans the length of the defect is then selected, ensuring that it does not interfere with the intervertebral disc spaces above and below the construct. We currently use a non-slotted plate with unicortical variable angle screws, allowing for dynamization and load-sharing of the graft/cage, but minimizing subsidence.  The plate should be placed in the midline to avoid lateral placement of the screws that could result in vertebral artery injury.  Prior to securing the plate, osteophytes should be removed with the high-speed carbide burr to allow the plate to lie flat along the anterior aspect of the vertebral bodies.^7,8  Final plate and screw placement is verified with orthogonal fluoroscopic images.

At the completion of instrumentation, the surgical wound is inspected for evidence of bleeding.  Thrombin-soaked sponges are placed along the medial borders of the longus colli and a surgical sponge packed into the wound to obtain hemostasis.  They are then removed and a Cloward retractor is placed into the wound and inspected to ensure hemostasis and to evaluate the anterior structures of the neck, including the trachea, esophagus, and carotid sheath.  The esophagus is then massaged as well by palpating the orogastric or nasogastric tube. 

A layered closure is performed over a 1/8 inch Hemovac drain, with a figure-of-eight, interrupted 3-0 monofilament suture to reapproximate the platysma layer.  The subcutaneous tissue is approximated with 4-0 absorbable suture in an interrupted, simple, buried manner.  This reproduces a subcuticular closure, but allows for the egress of fluid through the closure should a postoperative hematoma form.⁷  A sterile dressing is applied, and the patient is placed in a semi-rigid, short Aspen cervical collar.

Pearls and Pitfalls

• The most common reasons for asymmetrical corpectomy and injury to the vertebral artery are inadequate exposure (ie, lateral to the transverse processes and defining the lateral aspect of the uncinate) and failure to maintain midline orientation.
• Improperly placed Caspar pins (ie, off center) can induce a rotatory deformity during decompression and correction.
• Obtain the depth of the corpectomy by excising all disc material at the intervertebral interspace cephalad and caudad to the vertebral body being resected.  This allows the surgeon to remove bone safely and efficiently down to the posterior cortex.
• The use of a rongeur instead of a high-speed burr to perform the corpectomy allows the surgeon to generate local autogenous bone graft that can be used in conjunction with structural allograft or cages for reconstruction.
• Combining a corpectomy with adjacent level anterior cervical discectomy and fusion (ACDF) can be used in certain patients as it decreases the number of healing surfaces as compared to multilevel ACDF. Along with maintaining a native vertebral body, this may improve force distribution and effectively restore lordosis.
• A loose bone graft strut/cage general results from measuring the corpectomy site without traction on the spine.

Postoperative Care

• The average ACCF patient requires 1-2 days of hospitalization.
• If the operative time exceeds 3 hours, the patient remains intubated overnight in the intensive care unit, with extubation the following morning in an effort to reduce early post-operative airway complications. 
• A single dose of an intravenous steroid is given on the night of surgery to all patients after ACCF, and the patient is kept with the head of bed elevated above 60 degrees. 
• Antibiotic prophylaxis is continued for 24 hours post-operatively, and the drain is removed when the output is less than 20 mL over an 8-hour shift or at 48 hours post-operatively, whichever occurs first. 
• Ambulation is started the night of surgery, and 1 to 2 weeks after surgery a progressive walking/low impact cardio program is allowed. 
• Formal physical therapy is not necessary in most cases, and all types of overhead lifting activities are restricted until a solid fusion is obtained. 
• A short, Aspen cervical collar is worn at all times postoperatively for 6 weeks.

Outcome

There have been several recent publications whose aim was to assess the efficacy and clinical outcome of ACCF and ACDF for CSM. ^9,10,11,12  In terms of clinical outcomes and post-operative functional scores, these studies have yielded comparable results with no statistical difference between the two procedures.  In all studies, the post-operative increase in JOA scores for ACCF was statistically significant, with an average increase of 3.9.^9,10,11  Pre-operative JOA scores of <9, pre-operative duration of symptoms >12 months and high intensity spinal cord signals on MRI are important risk factors for only a fair recovery rate.¹¹ 

Due to lower numbers of fusion surfaces following ACCF, a systematic review of nine retrospective publications reported a union rate of 91.5% following corpectomy with strut grafting, compared to 72.3% following multilevel discectomy.¹²  However, the amount of blood loss and graft and hardware complications were significantly higher in ACCF as compared to ACDF.¹² 

There has yet to be a prospective, randomized control trial comparing these two anterior procedures. When deciding between the two, the risks of blood loss, graft dislodgement, and hardware failure in ACCF must be weighed against the risks of nonunion following ACDF.

Complications

Complications following anterior cervical spine surgery are classified as intraoperative, early post-operative and late post-operative. 

Intraoperative Complications

Intraoperative complications include:

• Esophageal injury
• Vertebral artery injury
• Dural tears
• Spinal cord injury
• Peripheral nerve injury¹³ 

Esophageal injury occurs because of inappropriate retractor placement or from direct trauma from a high speed drill or sharp instruments with a reported incidence of perforation of 0.2%-0.4%.¹³  The reported rate of iatrogenic vertebral artery injury is 0.3%, most commonly occurring due to an excessively wide corpectomy, oblique corpectomy, or off-center corpectomy or from anatomic variations in the vertebral foramen resulting in a tortuous vessel.¹³  These complications are often due to inadequate exposure and loss of midline orientation on the vertebral body during the corpectomy.  The reported incidence of a dural tear is 3.7%; however, patients undergoing a revision operation or patients with an OPLL have higher rates of dural tears.¹³  Following repair of the dura, most surgeons choose to place a lumbar CSF drain despite a watertight repair to prevent fistula formation.  The reported incidence of iatrogenic spinal cord injury ranges from 0.2%-0.9%, and intraoperative monitoring with evoked potentials is prudent.¹³ 

Early Post-Operative Complications

In the early post-operative period, acute airway compromise is the most concerning complication and can be due to a variety of reasons, such as hematoma formation, CSF leakage, hardware/graft dislodgement, or local soft tissue swelling and edema. Peripheral nerve injury can occur intraoperatively, but it is also a known complication during the early post-operative period.  C5 radiculopathy is a well-recognized complication due to the short nerve root and the possibility of impingement of the ventral aspect of the cord on the corpectomy trough.  The reported incidence of C5 radiculopathy following an anterior approach is 3.9%.¹⁴ 

Late Post-Operative Complications

In the late post-operative period, dysphagia is the most common and well-recognized complication, with a reported incidence of 28% to 57%. This typically resolves with time, and Lee et al found only a 1.3% rate of dysphagia at 24 months post-operatively.¹⁵ As with dysphagia, most patients with post-operative dysphonia, caused by recurrent laryngeal nerve injury, resolve with time.  Reported rates for the early post-operative period range from 2% to 30%, and persistent symptomatic vocal cord paresis range from 0.33% to 2.5%.¹³

References

1. Rhee JM, Yoon T, Riew KD. Cervical radiculopathy. J Am Acad Orthop Surg. Aug 2007;15(8):486-494.
2. Emery SE. Cervical spondylotic myelopathy: diagnosis and treatment. J Am Acad Orthop Surg. Nov-Dec 2001;9(6):376-388.
3. Wada E, Suzuki S, Kanazawa A, Matsuoka T, Miyamoto S, Yonenobu K.  Subtotal corpectomy versus laminoplasty for multilevel cervical spondylotic myelopathy: a long-term follow-up study over 10 years.  Spine.  2001;26:1443-8.
4. Rao RD, Gourab K, David KS. Operative treatment of cervical spondylotic myelopathy. J Bone Joint Surg Am. Jul 2006;88(7):1619-1640.
5. Riew KD, McCulloch JA, Delamarter RB, An HS, Ahn NU. Microsurgery for degenerative conditions of the cervical spine. Instr Course Lect. 2003;52:497-508.
6. Beutler WJ, Sweeney CA, Connolly PJ. Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach. Spine (Phila Pa 1976). Jun 15 2001;26(12):1337-1342.
7. Glattes RC, Taylor B, Riew KD. Controversies and perils: anterior corpectomy or multilevel discectomy. Techniques in Orthopaedics; 17(3):382-390.
8. Bae HW, Delamarter RB. Cervical vertebrecomy and plating. In Bradford DS, Zdeblick TA eds.  Masters Techniques in Orthopaedic Surgery: The Spine. Philadelphia: Lippincott Williams & Wilkins; 2004;47-66.
9. Song KJ, Lee KB, Song, JH.  Efficacy of multilevel anterior cervical discectomy and fusion versus corpectomy and fusion for multilevel cervical spondylotic myelopathy: a minimum 5-year follow-up study.  Eur Spine J.  2012 Apr 18 [Epub ahead of print].
10. Lin, Q, Zhou, X, Wang, X, Cao, P, Tsai, N, Yuan, W.  A comparison of anterior cervical discectomy and corpectomy in patients with multilevel cervical spondylotic myelopathy.  Eur Spine J.  2012;21:474-81.
11. Gao, R, Yang, L, Chen, H et al.  Long term results of anterior corpectomy and  fusion for cervical spondylotic myelopathy.  PLoS ONE. 2012;7(4): e34811.
12. Jiang, SD, Jiang, LS, Dai, LY.  Anterior cerivical discectomy and fusion versus anterior cervical corpectomy and fusion for multilevel cervical spondylosis: a systematic review.  Arch Orthop Trauma Surg. 2012;132:155-61.
13. Daniels AH, Riew KD, Yoo JU, et al. Adverse events associated with anterior cervical spine surgery. J Am Acad Orthop Surg. Dec 2008;16(12):729-738.
14. Yonenobu K, Hosono N, Iwasaki M, Asano M, Ono K.  Neurologic complications of surgery for cervical compression myelopathy.  Spine. 1991;16:1277-82.
15. Lee MJ, Bazaz R, Furey CG, Yoo J. Risk factors for dysphagia after anterior cervical spine surgery: a two-year prospective cohort study. Spine J. Mar-Apr 2007;7(2):141-147.