Corpectomy

(1)

Orthopedic Surgery, Inspira Health Network, Vineland, NJ, USA

(2)

Spine and Orthopedic Surgical Institute, Houston, TX, USA

(3)

Department of Orthopedic Surgery, Thomas Jefferson University, Egg Harbor, NJ, USA

Keywords

Anterior cervical corpectomy and fusionCervical spondylotic myelopathyCorpectomyPosterior longitudinal ligament

Introduction

Anterior cervical corpectomy and fusion (ACCF) is a surgical technique utilized to treat patients when a more generous decompression is required than capable with discectomy alone. By far, the most common condition treated with this technique is cervical spondylotic myelopathy (CSM). It is also utilized to remove vertebrae that have been damaged or otherwise deformed from trauma or neoplasms of the cervical spine. It is performed by removal of the affected vertebral body and associated intervertebral discs to allow for decompression of the cervical cord. A strut graft or cage construct is then placed into the void to stabilize the anterior column. Anterior plating can be used to provide stability and support during the fusion process. Segmental anterior plating is especially recommended when performing multilevel corpectomies due to the high incidence of early instrument failure [8, 17]. Furthermore, posterior instrumentation may be necessary to support multilevel corpectomies [18]. This chapter will discuss the application of ACCF in the clinical setting as well as technical aspects of the procedure.

Indications for Cervical Corpectomy

The presence of retrovertebral disease is the primary indicator for use of the corpectomy procedure. ACCF has been shown to be an effective procedure for decompressing the anterior spinal cord. Multilevel discectomies should be performed when feasible over corpectomy procedures. When retrovertebral disease is present and multilevel surgery is required, a hybrid discectomy/corpectomy procedure is a viable option [15, 16]. Cervical corpectomy has several advantages/disadvantages that a surgeon should consider when contemplating this technique for patients. Corpectomy is generally favored over multilevel anterior discectomy in cases of long segment ossification of the posterior longitudinal ligament (OPLL), traumatic disruption of the vertebral body, osteomyelitis, and neoplasms [3]. Essentially, all of these conditions require either expanded decompression in order to attain the desired clinical result or removal of the vertebral body to accomplish the clinical goal. This removal is necessary to provide space for appropriate anterior column support and/or is part of a treatment plan for proper resection. Corpectomy has the ability to provide a more complete decompression, especially when there is significant stenosis behind the vertebral body. Corpectomy also has the advantage of improved visualization, fewer bone-graft interfaces to heal and a greater surface area to help facilitate fusion [8]. Hence, the theoretical risk of pseudarthrosis is less with ACCF compared to multilevel ACDF. Fraser et al. performed a meta-analysis investigating the fusion rates between ACDF with plating and ACCF. The authors reported no significant difference between ACDF with plating and ACCF when investigating two level disease; for three level disease however, the authors reported that ACCF was associated with higher fusion rates than ACDF [5].

The disadvantages include greater approach morbidity per level, more technically demanding than discectomy only procedure, greater risk of vertebral artery injury, more bleeding, more exposure of the spinal cord with resultant risk of iatrogenic injury, higher implant and graft complication profile, subsidence, and risk of suboptimal postoperative sagittal alignment [13, 14].

Surgical Approach

The patient is positioned supine on the operating table after induction and intubation. A longitudinal bump is placed between the patient scapulae with a small pillow beneath the patient’s head in order to place the cervical spine into slight extension. Extreme caution must be taken when positioning the patient cervical spine and intubation to avoid neurological deterioration secondary to hyperextension of the stenotic canal in those patients with significant myelopathy. The patient’s arms are tucked at the side with shoulders taped caudally to help with proper visualization during exposure and lateral radiographs. Care should be taken to prevent excessive traction of the patient shoulders that may result in a brachial plexus injury. Pay careful attention to upper extremity neuromonitoring baseline potentials obtained before taping for comparison. It is helpful to take a fluoroscopic image before prepping in order to refine positioning. A decision should be made in regard to need for Mayfield tongs or Gardner-Wells (GW) tongs. The author prefers 15–20lbs of Gardner-Wells traction in addition to the use of vertebral distraction pins to obtain desired postop lordosis. This requires GW tong placement slightly anterior to the cervical axis of rotation.

The anterior cervical spine can be accessed from the right or left side depending on surgeon preference. A transverse incision is utilized for procedures involving one to two levels. For procedures involving three or more disc levels, a longitudinal or oblique incision may be used. The vertebral segments involved determine the location of the incision. There are palpable landmarks of the anterior neck that will help guide the surgeon to the appropriate location for the incision. The angle of the mandible demarcates the C2–3 interspace. The hyoid bone typically lies anterior to C3 level. The superior portion of the thyroid cartilage marks C4–5 interspace. The location of C6 can be determined via palpation of the cricoid cartilage or by palpation of the carotid tubercle which projects anteriorly from the transverse process. Intraoperative fluoroscopy can also be utilized to localize the operative level.

Once the incision has been made through the skin and subcutaneous tissue, the platysma is divided in line with the skin. Any superficial veins encountered must be protected or ligated if they cross the planes of dissection. The vein pattern encountered is most often a single vertical vein. However, infrequently a Y-shaped bifurcation is encountered and at other times two bifurcations may be seen. Be prepared to ligate the veins if bleeding is uncontrollable. Dissection is continued through the superficial layers of the investing deep cervical fascia between the sternocleidomastoid and the medial visceral muscle column. Next, the carotid sheath must be palpated. Blunt dissection is performed through the middle layer of deep cervical fascia between the esophagus and carotid sheath. The author prefers to use a Peanut sponge to sweep the fascia laterally while protecting the carotid sheath. This provides medial lateral dimension for the work necessary. The prevertebral fascia will then be visualized anterior to the vertebral column. This fascia is subsequently incised and dissected off the vertebral bodies. The medial borders of the longus colli muscles are now identified off of the midline. The midline can be marked at this point to reference for decompression and graft alignment later in the procedure. The operative level is marked and lateral fluoroscopy confirms the level.

Following the confirmation of the operative level, the longus colli is elevated using mono or bipolar cautery. The author prefers bipolar cautery as the bleeding of the dorsal or undersurface of the longus colli is better controlled with bipolar. It also helps the surgeon delineate when the mid-body bleeding is the result of a bone tributary versus muscle vein. Proceeding with the dissection, the longus is elevated from the level of the mid-vertebral body above and below the body of interest. Care must be taken to avoid dissection on the ventral surface of the longus colli muscles that may result in injury of the sympathetic chain causing Horner syndrome. Next, place retractors under the longus colli bilaterally.

Discectomies are subsequently performed both at the levels above and below the vertebral body(ies) planned for corpectomy(ies). The disc is removed to the level of the posterior longitudinal ligament (PLL). The next anatomic landmark that must be identified is the lateral cortical wall of the vertebral body. A Penfield 2 or 4 can help accomplish this task. This is the junction of the transverse process and vertebral body. Identifying the lateral cortical wall allows for the establishment of a symmetrical and central trough while avoiding injury to the vertebral artery which lies just lateral to this wall. A secondary landmark of reference is the uncovertebral joint on either side. This generally demarcates the lateral cortical wall of the vertebral body.

The most ventral portion of the corpectomy trough is created with a ronguer. This resected bone should be saved for autogenous bone graft. With the anterior cortex removed, a bur is utilized to expand the trough. Alternatively, the author prefers to use the Misonix Bone Scalpel® to osteotomize the body with 3 cuts. These chunks are then removed en bloc. At this juncture, the surgeon can overlay the graft to judge trough width and centrality. Resection is continued until the posterior cortex of the vertebral bodies is visualized. The cortical bone is less porous and less vascular than cancellous bone of the body. The posterior cortex can be removed with small angled curets by pulling the bone away from the PLL and dura or authors preferred method of using high-speed drill to cut longitudinal osteotomies creating a floating island of posterior cortex. This island is dissected free from PLL and removed. The PLL can be carefully removed via nerve hook and ronguer. Care must be taken in cases of ossification of the posterior longitudinal ligament (OPLL) as this ligament may be incorporated into the dura [9]. Removal of the ligament should not be attempted as this may cause a tear in the dura; it may be necessary to leave islands of ossification to avoid an anterior dural leak. It has been demonstrated that a safe and sufficient decompression requires approximately a 15 to 19 mm-wide trough [10, 11].

After adequate neural decompression has been achieved, the end plates are then prepared for insertion of the graft. The high-speed drill is used to remove endplate cartilage until fresh bleeding edges are visible. Take care to avoid endplate disruption. With adequate tension traction being applied to the head and/or distraction pins, the properly contoured graft or synthetic cage is gently placed. Assessment of graft stability is assessed with release of traction followed by manual flexion and rotation of the head by the anesthesiologist. Decorticate the uncinates and place autogenous bone graft in each exposed uncinate gutter. Segmental anterior plating is then performed.

A postoperative cervical collar is often placed on patients to provide additional immobilization [6].

Alternative Methods for Multilevel Corpectomy

As stated previously, ACCF has been shown to be an effective procedure for one- to two-level disease, but there is a higher rate of failure for three- and four-level cervical-plated corpectomy. Early construct failure is of particular concern in ACCF and that risk increases with constructs of three or more levels. Vaccaro et al. treated 45 CSM patients with two-level or three-level corpectomies with anterior plating in the absence of posterior instrumentation. The authors reported 9% dislodgement in the two-level group and a 50% dislodgement rate in the three-level group with migration of the graft occurring in over 80% of the three-level corpectomy even with the use of a halo [12]. A number of additional studies have also reported similar high rates of construct failure after multilevel corpectomy as well [7]. Without the addition of posterior instrumentation, the long lever arm created in anterior-only constructs creates instability which leads to graft migration and dislodgement [8]. The addition of posterior instrumentation is recommended to supplement multilevel ACCF to decrease the incidence of graft migration and dislodgement.

Another option for cervical disc degenerative disease affecting two or more adjacent levels includes a partial corpectomy which involves discectomies at the affected levels with removal of the anterior portions of the involved vertebrae leaving approximately one half to one third of the posterior portion of the body behind, strut graft, and anterior plating. Groff et al. conducted a retrospective study over a 9-year period investigating this technique with positive results. Some authors reported a fusion rate of 95.8% independent of the numbers fused. The authors asserted that their high fusion rate was due to improved stability with additional fusion surface area from the remaining vertebral body [4].

Cervical skip corpectomy is another method that can be used for compressions from C3–4 to C6–7. Skip corpectomy involves corpectomy at C4 and C6 with preservation of the C5 vertebral body as an intermediate point of fixation thus avoiding the use of a long strut graft. This technique also has the advantage of four healing surfaces as opposed to the eight surfaces associated with an equivalent ACDF. Ashkenazi et al. investigated skip corpectomy in 13 patients with CSM. The authors reported a 100% fusion rate and one case of mechanical failure (4%) [1]. Dalbayrak et al. also reported high fusion rates (100%) and low graft hardware-related complication rate utilizing this technique [2].

Technical Pearls

Measure the planned corpectomy width on the preoperative CT scan.
Identify the vertebral artery location on the preoperative CT and carefully scrutinize for aberrant vertebral artery anatomy.
Typically, 16 mm is a standard corpectomy width.
A large Leksell rongeur is usually 8 mm wide. Therefore, two rongeur bites side by side will be 16 mm.
Cut a paper ruler to the planned corpectomy width (16 mm). Throughout the case, the surgeon can bring that paper ruler into the operative field to ensure proper width.
The vertebral arteries are located at the mid-vertebral level. Therefore, at the posterior third of the vertebral body, more width can be accomplished if necessary.
Carefully identify the uncovertebral joints at the adjacent disc levels prior to the performance of a corpectomy. The standard corpectomy should move from Uncus to Uncus.
Advanced bone cutting tools, such as a bone scalpel or a Sonopet, may be useful for reducing the risk of vascular injury and for reduction of bleeding.
Take down the PLL at the disc levels prior to performing the corpectomy so that a clear plane is visible.
Carefully apply bone wax to the corpectomy walls to reduce bleeding.
Carefully measure the size of the planned graft on a preoperative CT scan (usually 25 mm).
Do not overdistract corpectomies or there is a substantial risk of graft subsidence and failure.
Test the corpectomy graft with a Kocher clamp (pulling anteriorly) to ensure that it does not displace with minimal force.
If necessary, omnipaque can be applied to the anterior epidural space in an angiocatheter to visualize the back of the corpectomy graft (if a tricortical ilium strip is used).