Anterior Cervical Corpectomy and Fusion and Hybrid Techniques

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Chapter Synopsis	Surgical decompression of the neural elements is of paramount importance in all spinal procedures, especially those of cervical myelopathy. Neural compression at the level of the disk space can be addressed by performing anterior cervical diskectomy and fusion. When the compression occurs posterior to the disk spaces, corpectomy is typically necessary. Multilevel corpectomies can result in mechanical instability, and therefore posterior stabilization is required. A novel hybrid technique that consists of a combination of corpectomies with diskectomies has been used to avoid the morbidity associated with posterior stabilization. The goal of this chapter is to provide a detailed description of this novel technique and the standard corpectomy, indications for these procedures, and perioperative concerns.
Important Points	A detailed history and physical examination should be performed and correlated with radiographs and advanced imaging studies to identify myelopathic patients. Indications for these techniques include symptomatic myelopathy with multilevel spinal cord compression posterior to the vertebral bodies. Contraindications include posterior compressive disease in patients with lordotic cervical alignment. Magnetic resonance imaging (MRI) is the advanced imaging modality of choice. It allows visualization of spinal cord signal change seen in myelopathic patients. Computed tomography myelogram is an option for patients who cannot undergo MRI; it may also provide additional information about osteophytes and ossification of the posterior longitudinal ligament (OPLL).
Clinical and Surgical Pearls	Preoperative imaging should be carefully studied for anatomic variations, such as an anomalous course of the vertebral artery. The uncinate processes should be clearly defined during exposure because this allows the surgeon to define the midpoint of the vertebral body. Straying off center can result in an eccentric corpectomy. Preoperative planning should include evaluation of the width of the vertebral body and knowledge of available cage sizes.
Clinical and Surgical Pitfalls	OPLL should be identified preoperatively to minimize the likelihood of a dural tear during the corpectomy. Neural compression posterior to the vertebral body cannot be addressed by cervical diskectomy. Inadequate or incomplete decompression should be avoided, regardless of the surgical approach selected.

The anterior approach to the cervical spine is used to address neural compression resulting from tumor, infection, trauma, or degenerative disease. Addressing ventral compression of the spinal cord from behind the vertebral body typically requires corpectomy. A thorough history and physical examination are always necessary; however, their importance cannot be underscored enough in patients with cervical myelopathy. Subtle findings of declining manual dexterity and balance difficulty should be screened for during both history taking and examination because the presence of myelopathy can dramatically alter treatment. These findings should be correlated with advanced imaging studies, of which magnetic resonance imaging (MRI) remains the gold standard. In patients in whom MRI is contraindicated, a computed tomography (CT) myelogram should be ordered. In addition to visualizing the neural elements, CT myelograms allow a more detailed evaluation of bony anatomy and spondylosis in the cervical spine.

Alleviating the compressive lesions from the spinal cord is of paramount importance in cervical myelopathy. When these lesions occur posterior to the disk spaces, simply performing anterior cervical diskectomy and fusion (ACDF) at the diseased levels is sufficient. However, when these lesions occur posterior to the vertebral body, corpectomy is necessary. Multilevel corpectomies can result in iatrogenic instability within the cervical spine and therefore have historically required supplemental posterior fixation. In selected cases, a hybrid technique that combines diskectomies with multilevel corpectomies can be performed to avoid the morbidity of posterior fixation. The goal of this chapter is to provide a detailed account of the surgical techniques and perioperative considerations for both anterior cervical corpectomy and hybrid techniques.

Preoperative Considerations

The classic signs and symptoms of cervical myelopathy should be elicited when obtaining a detailed patient history. Neck and arm pain may be present, but myelopathic patients with minimal to no pain may also be encountered. Typical symptoms include numbness and tingling in the hands or arms, decreased strength, diminished dexterity and coordination, and balance difficulty. Questions should center on tasks that require fine motor movements; patients will report difficulty buttoning buttons and picking up coins off the floor, and their handwriting may worsen.

Certain physical examination findings are indicative of cervical myelopathy and should be routinely evaluated. Flexion-extension radiographs of the neck may reproduce pain or electric shocks down the arms and back (Lhermitte sign). Strength and light touch in the upper extremities may or may not be normal. However, a careful monofilament examination of the palmar digits can reveal subtle impairment. Other physical examination findings suggestive of upper motor neuron disease include hyperreflexia, inverted radial reflex, Hoffmann sign, clonus, and Babinski sign. Tandem gait evaluation should be performed to assess coordination and balance.

Imaging studies should consist of anteroposterior, lateral, flexion, and extension views of the cervical spine ( Fig. 31-1 ). Sagittal and coronal alignment, as well as any dynamic instability, should be noted. MRI studies allow evaluation of the disks, spinal cord, nerve roots, and ligamentous structures. Compression of the spinal cord can lead to edema within the substance of the spinal cord itself that manifests as a hyperintense signal on T2-weighted images. In addition to the substance of the spinal cord, the vertebral arteries should be carefully evaluated on the MRI images. The vertebral artery most commonly enters the foramen transversarium at C6, but variability exists. Even when the vertebral artery resides within the foramen, it may take a medial course into the vertebral body; serious consequences can result if this is not identified preoperatively, and corpectomy is performed at that level.

MRI remains the imaging modality of choice; additional information can be gleaned from a CT scan with or without a myelogram. A more detailed depiction of the bony anatomy can be appreciated, and in revision procedures, previous fusions can be assessed. Regardless of the imaging modality selected, the surgeon must be able to extrapolate a three-dimensional understanding of the neural compression from two-dimensional images. This understanding allows the surgeon to determine whether diskectomy, corpectomy, or a hybrid approach is appropriate.

Surgical Considerations

Adequate decompression can be achieved from either an anterior or a posterior approach, depending on the patient’s alignment and direction of compression. Kyphosis that does not correct in extension typically requires an anterior approach. In the kyphotic spine, performing posterior decompression for anterior compressive disease does not allow posterior migration of the spinal cord. The patient will continue to be symptomatic from the neural compression postoperatively.

Neural compression that occurs posterior to the disk spaces can be easily addressed with ACDF. Compression that occurs posterior to the disk spaces may require corpectomy. Extruded disk fragments located posterior to the vertebral body, but near the disk space, can sometimes be removed with a ball-tipped micro-nerve hook. However, if the extruded fragment cannot be removed in this manner, corpectomy becomes necessary. In the setting of ossification of the posterior longitudinal ligament, less ambiguity exists. Compression posterior to the vertebral bodies requires corpectomy to be addressed anteriorly. For multilevel ACDF procedures, corpectomy can reduce the number of healing surfaces and can potentially improve fusion rates. Multiple corpectomies, however, can destabilize the spine because of the long lever arms involved. Patients in whom such constructs are contemplated should be considered for a hybrid construct. In this construct, segmental fixation is placed within the intervening retained vertebral bodies to increase construct stability and preclude the need for posterior fixation.

A previous anterior surgical procedure is a relative contraindication to a secondary anterior procedure. Performing the approach through the contralateral side allows the surgeon to avoid scar and work through native tissue planes. However, the competence of the recurrent laryngeal nerve and vocal cords must be assessed preoperatively by direct or indirect laryngoscopy. Injury to the recurrent laryngeal nerve on the previously operated side should dissuade one from approaching the cervical spine from the contralateral side because this may lead to bilateral vocal cord paralysis.

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