Endoscopic Anterior Cervical Diskectomy and Cord Decompression

45 Endoscopic Anterior Cervical Diskectomy and Cord Decompression

Shrinivas M. Rohidas

45.1 Introduction

Degenerative changes at vertebrae and the intervertebral disks occur due to wear and tear after constant use of the spine, among other reasons accelerating the degeneration. Degenerative changes in the spine have two main effects. One is compression of the neural structures, and the other is increased motion at the joints involved. Neural compression can be either with or without instability at the motion segment. When there is a compressed nerve or cord, the surgical treatment is to create more space for the nerve or cord. At the same time, the surgical procedures for decompression should not compromise the stability of the motion segment. In the cervical spine, Endospine makes it possible to treat endoscopically the compressed nerve and the cervical cord. In 1996, Jho described a microscopic anterior cervical foraminotomy procedure where the transverse process and uncovertebral joint were exposed and the decompression was performed with gradual removal of the uncinate process so as to reach the nerve root.1,2

45.2 Surgical Indications

Degenerative cervical pathology includes nerve compression, causing radiculopathy; cord compression, causing myelopathy; or nerve and cord compression, causing myeloradiculopathy. In young patients, most of the time the compression is due to soft disk herniation, and in elderly patients, compression is due to osteophytes, hard disks, and hard posterior longitudinal ligament.

Endospine can be used for anterior endoscopic cervical foraminotomy with Jho’s approach and anterior endoscopic cervical foraminotomy and partial vertebrectomy with Jho’s approach. This is indicated for soft or hard foraminal disk herniations. In elderly patients, the disk can be very small, or hard, or nonexistent, but the nerve and cord are compressed, leading to myelopathy and/or myeloradiculopathy. In these pathologies, anterior endoscopic foraminotomy can be easily extended to the opposite side, up to the midline or where the foramen begins (Fig. 45.1, Fig. 45.2).^3,4,5

45.3 Technique

We use Endospine, a straight, rigid, 0°,18-cm endoscope, a high-definition (HD) camera, an endoscopic drill, 2-mm and 3-mm tip burs, ultrasonic bone dissector, and endoscopic bipolar cautery. The rest of the instruments are similar to those used in conventional cervical spine surgery—for example, a 2-mm Kerrison punch, 45° and 90° nerve hook, Penfield dissector No. 4, scissors, etc. Bone removal is performed with 3-mm and 2-mm cutting high-speed drills, which can be used through the working channel of Endospine. The ultrasonic bone dissector is used to remove bone near the vertebral artery, nerve root, and cervical cord, so as to protect these important structures. The ultrasonic bone dissector will emulsify bone and will not damage the soft tissue nearby.

Fig. 45.1 Cervical nerve root and cord compression due to degenerative changes. Courtesy of Dr. W. Rauschning.

Fig. 45.2 Cervical nerve root and cord decompression through transuncal approach with Endospine in cadaver dissection.

45.4 Patient Positioning

All operations are performed with the patient under general endotracheal anesthesia. Patient positioning is similar to that for conventional anterior cervical discectomy, with the head straight without turning and the neck neutral without turning to opposite side. For patients with a short neck, we use shoulder traction bilaterally to pull both shoulders caudally. In some patients who have a short neck, slight neck extension is used. Precaution during neck positioning is important to prevent position-induced injury to the cervical cord, especially if the patient experiences aggravation of symptoms upon neck extension preoperatively.

45.5 Use of Cervical Localization Pin

For the endoscopic anterior cervical approach, exact localization of the disk level is very important to minimize approach-related tissue trauma. The special localizing pin can be moved in three spatial planes. After exactly localizing the pathological disk level, the entry point is determined, as well as the direction of the disk space, so that the anteroposterior foraminotomy can be aimed to reach the nerve root and cord. In spite of the exact localization of the disk space, the level is confirmed with the help of the C-arm after exposure of disk space, before starting bone removal (Fig. 45.3, Fig. 45.4).

45.6 Skin Incision

Skin incision is horizontal, as in an open cervical approach. After exact localization of the disk level, the incision is approximately one-third lateral and two-thirds medial to the sternocleidomastoid muscle. Then the platysma is cut, and the soft tissues are dissected between the carotid laterally and the trachea-esophagus medially, with the help of fingers. The anterior aspect of the cervical spine is exposed. At this point, the transverse processes can be palpated with the finger under longus colli muscle. The C6 transverse process can be easily identified with the help of the bony prominence of the carotid tubercle. Two thin blades of the cervical retractor system are used to retract the carotid artery laterally and the trachea and esophagus medially. Then the outer tube of the Endospine with an obturator is placed between the retractor blade switch are retracting the vascular and visceral axis. The blades of cervical retractor system are used without the holding arms of the retractor. Through the outer tube, with the help of scissors, the medial part of longus colli is cut over the disk space concerned. One to two millimeters must be removed from the medial part of the longus colli muscle. This will avoid trauma to the sympathetic chain, which is located more laterally, and will expose the disk space and the uncovertebral joint laterally. At this point, once again the C-arm is used to confirm the disk space level to be targeted.

Fig. 45.3 Cervical localizing pin to localize disk space and disk direction.

Fig. 45.4 Patient with cervical localizing pin.

Fig. 45.5 Endospine with endoscopic drill.

45.7 Endoscopic Foraminotomy

Now the working insert with the 4-mm rigid telescope is introduced through the working channel of the Endospine. With the help of HD vision, the disk space, uncovertebral joint, and transverse processes of the cranial and caudal vertebrae are defined (Fig. 45.5).

The working area for the surgeon is between the two transverse processes and medial to the vertebral artery. The nerve root leaving the dural sleeve and reaching the vertebral artery measures approximately 6 mm. Then bone removal is performed using the 2- or 3-mm cutting/diamond pencilgrip high-speed drill (Fig. 45.6).

The bony window measures approximately 8 to 10 mm in the craniocaudal direction and 5 to 8 mm in the transverse direction. During creation of the bony window, part of the disk medial to the uncovertebral joint is removed. The Endospine with endoscope is at an angle of 15 to 30°, in order to reach the lateral part of the disk and vertebral bodies. The disk has to be followed laterally and cranially toward the uncovertebral joint. The uncovertebral joint is cranial to the disk space concerned. While widening the bony window, we drill out the osteophytes from the cranial and caudal vertebral bodies, which opens the neural foramen. The spinal canal is reached just at the medial part of the neural foramen, where the herniated soft disk is most often found. The nerve root is exposed and is decompressed from the spinal canal or lateral edge of the dural sac until the nerve crossing the vertebral artery is reached. This tunnel is ~ 6 mm in diameter and follows the oblique direction of the nerve root. Therefore, it enlarges the intervertebral foramen in front of the nerve root (Fig. 45.7). Left-sided C4–C5 foraminotomy and nerve root decompressed from the dural sac are shown in Fig. 45.8 and Fig. 45.9. The preoperative left-side C4–C5 disk herniation sagittal and axial views are shown in Fig. 45.10 and Fig. 45.11, and postoperative sagittal and axial views are shown in Fig. 45.12 and Fig. 45.13.