Anterior Cervical Foraminotomy

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Chapter Synopsis	This chapter describes in detail the surgical techniques and merits of transcorporeal anterior cervical microforaminotomy for cervical radiculopathy. This procedure involves a modification of the previous anterior microforaminotomy in terms of its medial starting point and tunneling on the upper vertebral body.
Important Points	Transcorporeal anterior cervical microforaminotomy allows for direct decompression of the cervical nerve root while preserving the uncovertebral joint and intervertebral disk integrity and avoiding injury to the vertebral artery and cervical sympathetic chain. Indications include cervical radiculopathy secondary to compression anterior or medial to the cervical nerve root. Contraindications include bilateral foraminal stenosis, predominant axial neck pain, signs suggestive of infection, mechanical instability, and cervical myelopathy.
Clinical and Surgical Pearls	Foraminal magnetic resonance imaging and reconstructed computed tomography images perpendicular to the cervical foramen can help identify and define the foraminal disease. Typically, the anterior cervical exposure to the upper vertebral body and affected disk space is approached from the side corresponding to the radiculopathy. The longus colli muscle is dissected from its medial border. The starting point for microscopic drilling is just lateral to the medial margin of the longus colli muscle at the midvertebral body level heading toward the posterior tip of the uncinate process. In the case of spondylotic foraminal stenosis, the ideal decompression is limited by the upper and lower pedicle and full lateral bony decompression to the transverse foramen. In the case of soft disk herniation, the surgeon must excise the posterior longitudinal ligament to explore for any residual free fragments penetrating the ligament.
Clinical and Surgical Pitfalls	Care should be taken not to violate the upper vertebral end plate because that can result in late intervertebral disk collapse and narrowing. Uncertainty of the sagittal orientation tends to bring about more caudally directed drilling. Usually, a 15-degree caudal angle on the sagittal plane is appropriate. Tilting the patient to the proper angle can place the desired drill hole perpendicular to the ground in both the sagittal and axial planes. In the case of the extruded disk, a careful search for additional extruded fragments must be performed if intraoperative findings do not confirm preoperative imaging results.

Cervical radiculopathy is mainly caused by anterior cervical disorders, including cervical disk herniation and uncovertebral osteophytes. Smith and Robinson and Cloward established the anterior approach to treat the cervical spine. In 1968, Verbiest reported using the anterolateral approach for cervical foraminal stenosis, and in 1976, Hakuba introduced the transuncodiskal approach. In 1996, Jho reported transuncal microforaminotomy, which was similar to the Hakuba technique but simpler, preserving the disk. Choi and colleagues proposed a modification of upper vertebral transcorporeal anterior cervical microforaminotomy (ACF), which starts with a drill hole at a relatively medial position compared with the previous technique. This newer concept of transcorporeal ACF offers direct decompression of the cervical nerve root while preserving the uncovertebral joint and intervertebral disk integrity and avoiding injury to the vertebral artery and the cervical sympathetic chain. The goal of this chapter is to review the preoperative and postoperative considerations, surgical technique, complications, and results of ACF procedures.

Preoperative Considerations

Eligible patients are those with persistent unilateral cervical radiculopathy and pain unresponsive to conservative treatment for longer than 6 weeks. If patients continue to have severe radicular symptoms not alleviated by opioids or have profound motor deficits, consideration for earlier operative intervention is indicated. Physical examination that shows a positive Spurling sign and weakness or sensory loss in a corresponding pain dermatome secondary to cervical radiculopathy can be expected. However, examination findings consistent with myelopathy, such as a positive Lhermitte sign or Hoffmann sign, are considered contraindications to ACF.

The required preoperative imaging study includes oblique and dynamic flexion and extension lateral radiographs, magnetic resonance imaging (MRI), and computed tomography (CT) scan. Foraminal MRI, which consists of axial MRI images obtained perpendicular to the cervical foramen, is also helpful in evaluating foraminal disorders. The extension of disk herniation or osteophytes, calcification and migration of disks, and location and variation of the vertebral artery in the transverse foramen should be checked in preparation for the operation. Axial CT scan and sagittal CT reconstruction images are useful in determining the location of the drill hole and for measuring the transcorporeal trajectory.

ACF is indicated when the history and examination confirm persistent unilateral radiculopathy that correlates with preoperative imaging studies demonstrating posterolateral disk herniation or uncovertebral osteophytes that compress the cervical nerve root anteriorly. In patients with multilevel disease or vague symptoms, electrophysiologic study, including nerve conduction velocity and electromyography, may help confirm the diagnosis. Multilevel foraminal stenosis and disk herniation are not often present and also can be indications for ACF ( Fig. 33-1 ).

Bilateral foraminal stenosis, predominant axial neck pain, signs suggestive of infection, instability, and the presence of myelopathy are contraindications to ACF. Unilateral foraminal decompression performed in the presence of bilateral foraminal stenosis may aggravate the development of radiculopathy on the contralateral side. Axial neck pain secondary to degenerative cervical disk disease is also a contraindication to ACF. Anterior cervical diskectomy and fusion (ACDF) may be an option in patients who are not candidates for ACF.

Surgical Technique

The patient is placed supine, with the neck in an extended position. General anesthesia is used. Both shoulders are slightly pulled caudally and are maintained by adhesive tape to help improve intraoperative radiographic visualization. The level of the intended skin incision can be confirmed on the lateral radiograph and should be centered on the upper portion of the vertebral body of interest.

The surgical approach is made on the affected side. After preparation and draping, a 3-cm transverse skin incision along the skin crease is made. Because the trajectory of the drill hole is in the cranial-to-caudal direction, the skin incision should be centered on the upper portion of the vertebral body. The fascial plane just medial to the carotid sheath is sharply incised and bluntly dissected to the anterior surface of the vertebral body. After identifying the midline, the surgeon opens the prevertebral fascia layer longitudinally and detaches the longus colli muscle from its medial margin to the lateral margin of the uncovertebral joint.

Identifying the lateral margin of the uncovertebral joint and vertebral body is important to help determine the starting point of the drill hole. Unlike in ACDF or transuncal anterior foraminotomy, the upper vertebral body and affected disk space must be exposed, and the lower vertebral body does not need to be exposed for transcorporeal ACF. Self-retaining Casper retractors (Aesculap, Tuttlingen, Germany) are applied under the longus colli muscle laterally and the tracheoesophageal complex medially ( Fig. 33-2 ). Cranial-to-caudal retraction is not usually necessary if subfascial dissection is sufficient; however, in the patient with thick neck muscles, a narrow retractor is applied for craniocaudal retraction.

To confirm the accurate level, an 18-gauge needle is inserted at the expected point of the drill hole on the upper vertebral body ( Fig. 33-3 ). The needle must be inserted perpendicular to the anterior surface of the vertebral body. This placement helps to confirm the level of vertebral body exposure and also guides the direction of the drill hole compared with the vertical position of the needle. The entry point is at the midbody level (or 4 to 6 mm above the lower border of the exposed vertebra), just lateral to the medial margin of the longus colli muscle ( Figs. 33-4 and 33-5 ). This starting point is relatively more medial compared with earlier described techniques. The transuncal ACF first reported by Jho was to preserve the motion segment and to accomplish adequate anatomic decompression of the spinal canal anteriorly in the transverse and longitudinal axis, as well as the ipsilateral foramen. However, with this technique, the vertebral artery may be exposed and endangered because the hole is drilled at the most lateral portion of the vertebral body.