Cervical Discectomy

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Chapter 76 Cervical Discectomy

Indications for Cervical Discectomy

Age-related degeneration as well as trauma can lead to disc pathology requiring surgical excision. Commonly accepted indications for cervical discectomy include myelopathy and persistent radiculopathy that is unresponsive to nonsurgical measures.1,2 Less commonly accepted indications include axial neck pain and/or headaches3 that can be attributed to the disc pathology. The pathologic cervical disc can be approached ventrally and dorsally. Both approaches have been in use for over a half century48 and still find utility today.

The dorsal approach is indicated for a soft, foraminal (lateral) disc herniation with radiculopathy.1 One of the major advantages is that the posterior approach can be performed via a “keyhole” foraminotomy without creating instability at the segment. Disadvantages include the technical challenges (positioning, epidural bleeding, wound complications) and the surgeon’s learning curve, as this procedure is less commonly performed than is the more versatile ventral approach in most centers. Additionally, central disc herniations, “hard” disc herniations with uncovertebral bone spurs, and myelopathy are not adequately addressed via this approach. The dorsal approach for a discectomy via a foraminotomy can be accomplished with a small traditional midline incision and a self-retaining retractor9,10 or with a tubular retractor system.11

The ventral approach is very familiar to most spine surgeons. In most patients, the C3-4 level down to the C7-T1 level can be approached via a standard ventrolateral approach. Advantages of the ventral approach include access for central and bilateral foraminal decompression. Although some authors have reported good results for anterior discectomy without interbody fusion, interbody fusion following discectomy has become the standard of care in most centers. Recent trends include the use of allograft along with ventral cervical plates.12 Cervical disc arthroplasty devices are now available and can be used for postdiscectomy reconstruction; excellent results have been reported in properly selected patients.13,14

Anterior Cervical Discectomy

Anterior Cervical Discectomy and Fusion Technique

Preoperative Planning

It may be appropriate in revision settings to get a preoperative otolaryngology consult to evaluate vocal cord paralysis.15 If a vocal cord paralysis exists, the approach should be made on the ipsilateral side to avoid a potential bilateral paralysis. An approach on the right side may put the recurrent laryngeal nerve at more risk, while a low approach on the left side may put the thoracic duct at risk.

Intraoperative Procedures

The anesthesiologist administers 10 mg of intravenous decadron to minimize ventral swelling and prophylactic antibiotics (usually cefazolin 1 g) to minimize the risk of infection.

The patient is placed supine on the operating table. Neck flexion should be minimized in moving a patient with a large cervical disc herniation and myelopathy. A folded sheet or an intravenous bag is placed underneath and across the shoulders; sometimes, two sheets will be better. The sheets under the shoulders and the foam doughnut under the head are adjusted to obtain ideal neck extension (it is important to be careful in using two sheets, which may overlordose the cervical spine). It is rare that any support other than the foam doughnut is needed under the head. An unrolled Kerlix is placed around both wrists (NYOH stockinette-style knot) and hung off the bottom of the table to allow pulling down of the arms and shoulders for intraoperative radiographs. Plastic self-adhesive drapes are placed just above the nipple line and along both sides of the neck as low as possible. The side drapes are placed dorsal to the ear and around the circumference above the chin. The upper thorax should be accessible in case of emergency (e.g., vertebral artery injury and necessity for exposure of subclavian artery for proximal control). A half sheet is placed down over the patient’s body and legs to prevent accidental contamination via the surgeon’s gown touching the bed or patient. Sterile towels are placed over the sterile field and moved away from the center. The inferior towel is usually at the sternal notch; the superior towel is around the chin; the ipsilateral towel is as low as possible; the contralateral towel is several centimeters lateral to midline to accommodate a midline-crossing incision. The carotid tubercle, thyroid cartilage, and cricoid cartilage can be palpated as landmarks. The incision location can also be based on the location of the mandible and clavicle on preoperative radiographs. An incision is marked in a neck crease if possible, crossing midline as needed. Perpendicular lines help during closure. Larger transverse incisions with less retraction (skin stretching) tend to heal better than a smaller incision with stretched skin edges. Vertical incisions leave unappealing scars and can be avoided. The incision should be located in the inferior third of the levels to be decompressed because it is easier to mobilize skin in a cephalad rather than a caudad direction and the disc spaces angle cephalad. The skin is injected with 0.25% Marcaine with epinephrine as early as possible, since the epinephrine takes time to work (ideally 10 minutes). Cut strips of adhesive barrier drape (Ioban) are used to seal the edges after the incision is marked.

A scalpel is used to incise the epidermis and dermis. Leaving an intact corner of dermis at the ends of the wound protects against stretching, thereby allowing for a more cosmetically pleasing closure. Subcutaneous bleeders can be cauterized but will often tamponade with a gently placed Weitlaner retractor that is spread gradually during exposure. Using the cut function on the electrocautery will minimize charred tissue, but small veins will often need the coagulate function. The platysma is cut transversely in line with the incision; sometimes, veins run in the platysma layer and can be dissected bluntly with Metzenbaum scissors or directly coagulated with the cautery. The platysma is undermined cranially and caudally with spreading scissors, blunt finger dissection, and cautery. When multiple segments are being exposed, the platysma should be undermined from the corner of the mandible to the clavicle along the length of the sternocleidomastoid. The interval between the sternocleidomastoid and medial strap muscles is identified. The external jugular vein may be mobilized either laterally or medially. Preserving the sternocleidomastoid fascia by starting the dissection closer to the strap muscles will minimize bleeding. Spreading scissors, blunt finger dissection, and cautery are used to dissect through the interval between the alar fascia (carotid sheath) and the visceral fascia (trachea and esophagus). The carotid pulse can be palpated and kept lateral. In the interval, the ventral cervical spine and longus colli muscles can be palpated. Blunt finger dissection can widen the defect longitudinally, although there may be less bleeding with the spreading scissors technique. Crossing nerves that should be preserved include the glossopharyngeal and hypoglossal nerves at the very top of the approach and the superior laryngeal nerve above the superior thyroid artery. The recurrent laryngeal nerve may be at the bottom of the approach, especially on the right side. It is acceptable to take the inferior, middle, and superior thyroid vessels if necessary. Larger crossing vessels may need to be tied. A wall bleeder can be very difficult to stop if it represents a side-opened vessel; in this case, a bipolar technique will often slow bleeding enough to allow packing with a hemostatic agent and cottonoid patty. A hand-held retractor is placed medially to pull the trachea and esophagus over the midline to see the ventral aspect of the cervical spine. The omohyoid muscle crosses the field around C6 and can be divided with lower-level dissections with no adverse effects. The muscle can be elevated with Metzenbaum scissors underneath and then divided with electrocautery.

The carotid tubercle, usually at C6, and ventral osteophytes can be palpated to estimate levels. The prevertebral fascia is cleared off the discs (hills) and vertebral bodies (valleys) using scissors and forceps with a nick-and-spread technique. The hand-held retractor is then replaced under this layer (Fig. 76-1).

Once the radiology technician is present, a bent 12-mm, 14-mm, or 16-mm spine needle (based on preoperative radiographic measurement) is placed in the disc space of choice. The carotid tubercle and/or ventral osteophytes can be used to predict the level (Fig. 76-2). Dissection can continue while the film is being processed. The sterile draped microscope is then brought into the field. The “valley” of the ventrolateral aspect of the vertebral body above and below the suspected disc is cauterized to get the segmental arteries and perforating branches. The longus colli is elevated off the vertebral body “valley” by using coagulate (cranial and caudal enough to place the plate comfortably) and then off the ventral disc “hill.” The safe (nonanomalous) position of the vertebral artery should be confirmed on the preoperative axial MRI or CT prior to elevation of the longus. The longus colli in the upper cervical spine (i.e., C3-4 and higher) is less muscular and less well defined. A Penfield 2 can be used to safely elevate the longus at the vertebral body out laterally over the transverse process. Bleeding bone on the front side of the vertebral body under the elevated longus can be coagulated with bone wax used as needed. If bleeding starts from the undersurface of the longus or out laterally, a hemostatic agent and a large cottonoid patty can be used. The self-retaining (Shadowline or similar) retractors are placed underneath the elevated layer of the longus colli. The hand-held retractor is used to move the esophagus so that the self-retaining retractor blade can be safely placed under the longus. An assistant’s hand on the medial self-retaining retractor handle can stabilize downward and keep it correctly positioned (Fig. 76-3). The vertebral body just cranial and caudal to the disc space is prepared for insertion of the Caspar retraction posts. Prior to insertion of the Caspar pins, a rongeur or bur is used to remove the ventral osteophytes until they are flat with the ventral surface of the vertebral body. Caspar pins (usually 14 mm or 16 mm based on preoperative and localizing radiographs) are inserted by hand. Careful insertion is important if the patient is very myelopathic or stenotic. The superior post should be farther away from the cranial inferior end plate, but the inferior post is just below the caudal superior end plate. This is due to the angled shape and orientation of the cervical vertebral bodies, and will allow good purchase of the screws. The Caspar pins can be inserted slightly diverging to allow for lordosis. Proper insertion of the Caspar posts is critical. The posts must both be in the center of the vertebral bodies, since going off center with one post may result in vertebral twisting and scoliosis after the Caspar retractor is placed. If the posts are not placed in the center but are both off to one side, the distraction of the interspaces will be asymmetrical and lead to uneven end-plate preparation while the posts are retracting. Excellent visualization of the bodies before placing the posts will help to avoid errors at this step. Centering with reference to the spine is more reliable than centering with reference to the patient’s chin and sternal notch. The cranial angulation of the disc space should be parallel to the path of the Caspar pin in the sagittal plane. It can be helpful to identify the disc space with a Bovie or #15 blade if the surgeon is unsure of the location or angle. The posts must diverge or be parallel when inserted to lordose the spine and prevent the cephalad post from entering the end plate, given the upward sloping nature of the end plate. If the Caspar pins are not placed divergently, the threads of the cephalad post may be encountered while burring out the end plate.