Cervical Discectomy

Summary of Key Points

•

Successful discectomy can be performed from an anterior or posterior approach.
•

Each approach has specific risks and benefits.
•

Central herniations typically require an anterior approach.
•

Fusion is typically indicated following anterior discectomy.
•

Fusion techniques vary, but nonunion continues to be a clinically relevant problem.
•

Disc arthroplasty is a more recent alternative to reconstruct an anterior discectomy.
•

Indications for disc arthroplasty are more limited than those for fusion.

An anterior cervical discectomy and fusion and a posterior foraminotomy and discectomy are among the simplest, most popular, and most effective spine operations ever invented. Despite being so common, because of all the possible permutations on the technique, it is likely that no two surgeons do these procedures in exactly the same manner. In this chapter, we describe our technique for doing both. Although we make no claims that this is the best possible technique, we have found that, in our hands, as well as those of our fellows, these techniques help to minimize complications and maximize results. Our fellows are required to memorize these steps and to perform these operations in exactly the same step-by-step manner every time. By doing so, new trainees, and even experienced spine surgeons, can become more efficient surgeons. In addition, by memorizing each step and performing the procedure in exactly the same manner every time, the scrub nurse can learn the steps and know what tools to hand to the surgeon. The surgeon can make the procedure more efficient by asking for the instrument needed for the next step while performing the current one. This gives the nurse time to find it and to get it ready to hand off to the surgeon.

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. Less commonly accepted indications include axial neck pain and headaches 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 century and still find utility today.

The dorsal approach is indicated for a soft, foraminal (lateral) disc herniation with radiculopathy. 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 in most centers than is the more versatile ventral approach. 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 retractor or with a tubular retractor system.

The ventral approach is 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. Trends include the use of allograft or synthetic interbody devices along with ventral cervical plates. Nonunion continues to be a clinically relevant problem that can lead to the need for re-operation. Cervical disc arthroplasty devices are now available and can be used for postdiscectomy reconstruction; although the indications are more limited, excellent results have been reported in properly selected patients.

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. 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, whereas a low approach on the left side may put the thoracic duct at risk.

Preoperative Imaging

The preoperative radiographs are examined to identify unique anatomic features. The proper identification of existing instrumentation is especially important to ensure that all needed equipment will be available. Knowledge of the ventral osteophytes can help the surgeon to identify the proper levels during the approach by intraoperative palpation and visualization. The vertebrae are labeled by level, and the anterior-to-posterior distance of the vertebral body (minus the magnification factor) is measured to estimate the graft and screw size. Anatomically “short” necks where the lower cervical levels are at or below the level of the clavicle may alert the surgeon to potential difficulty accessing these lower levels during a standard approach. It may be helpful to list the patient’s symptoms (especially left versus right, radiculopathy or myelopathy), surgical plan (levels of discectomy), and important comorbidities (smoker, diabetic, etc.). The axial magnetic resonance imaging (MRI) or computed tomography (CT) scan should be carefully reviewed for the vertebral artery position, and any anomalies should be carefully noted. The operative site is marked in the holding area.

Exposure

The anesthesiologist may administer 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. Wrist restraints or 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 along Langer’s lines, in a neck crease if possible, crossing the 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, because 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 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 handheld 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 retracted caudally and medially with the trachea for upper level exposures. Caudal retraction may help protect the recurrent laryngeal nerve on the right side. Alternatively, the omohyoid can be divided with lower-level dissections with no adverse effects typically noted. The muscle can be elevated with Metzenbaum scissors underneath and then divided with electrocautery. Beginners will often find their dissections stuck in the axilla of this muscle belly, instead of lateral to it. This limits the cranial extent of the dissection and increases the force necessary to retract the soft tissues. Therefore, early identification of the muscle is necessary to prevent this from happening.

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 handheld retractor is then replaced under this layer ( Fig. 71-1 ).

A Burlisher clamp or long hemostat is placed on the edge of the longus coli to localize the level. We prefer this to placing a needle in the disc space, as doing that in an uninvolved disc may cause injury by initiating or acceleration disc degeneration. If one is trying to localize one of the lower cervical levels in a patient with a short neck, it is preferable to place hemostats at multiple levels starting at C3-4 or C4-5 and count down to the operative level, as lower levels may not be visible. We use a spot C-arm image, which is faster than using plain radiographs. We inspect the films for three things: first, that we have the correct surgical level; second, that we have the right patient; and third, that the patient’s neck alignment is not hyper- or hypolordotic. Once the level has been localized, we mark the disc space by cauterizing it until it is impossible to mistake for an unmarked level. It is surprising how a small mark can disappear once it is bathed in blood. The radiology technician is now allowed to leave the room, as no further shots will be taken until the instrumentation goes in. The sterile draped microscope is then brought into the field.

We next elevate the longus colli muscle. There are two dangers associated with this. The first is that the vertebral artery can be injured, especially if it is anomalously located anterior to the foramen transversarium. Therefore, 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 second risk associated with elevating the longus has to do with the small arterioles that lie ventral to the longus that perforate the anterior vertebra at the medial aspect of the longus muscle. If this is cut with a monopolar electrocautery, it will sometimes retract and stop bleeding, only to open up again a few hours postoperatively, resulting in a retropharyngeal hematoma. We avoid this complication by first identifying these vessels on top of the longus and cauterizing them with bipolar electrocautery. Then we stick the bipolar under the muscle in the “valley” of the ventrolateral aspect of the vertebral body above and below the suspected disc and cauterize the segmental arterioles where they perforate into the vertebral body. We elevate the longus out to the lateral aspect of the costal process (anterior roof of the foramen transversarium) with a Penfield 2 and cauterize the periosteum. This technique helps to ensure that the segmental arterioles will not bleed postoperatively. As a final precaution, we wrap the edges of this muscle at the end the case with Surgicel. If bleeding recurs from the undersurface of the longus or out laterally, bipolar cauterization or a hemostatic agent and a large cottonoid patty can be used. At this point, the handheld appendiceal retractor is replaced with self-retaining (Shadowline or similar) retractors, which are placed underneath the elevated layer of the longus colli. Because these retractors tend to tip away from the esophageal side, we leave the retractor handle on that side while removing it from the other side. The weight of the handle helps to keep the retractor blades in place.

Smooth Off All Osteophytes.

Before placing the Caspar pins, it is critical to smooth down the anterior aspect of the vertebral body with a rongeur or a bur. This is important for two reasons. First, one can size the length of screws needed for the plate by placing the screw in the disc space, and this is done more accurately if all the osteophytes have been removed. Second, if the body is not made smooth at this point, it is easy to forget to do so at the end of the case. This will cause the plate to sit proud on top of the osteophyte instead of flush with the body, increasing the risk of dysphagia. The osteophytes can be saved for local autograft.

Pin Placement.

It is also important to choose an appropriate starting point, as well the directional angle of the Caspar pin. The superior post should be approximately 7 to 10 mm from the cranial level’s end plate. This is because the cranial end plate is concave, and one needs to resect more of its overhang to smooth it out. If the pin is too close to the end plate, it will not be possible to adequately smooth down the end plate. Also, the threads of the pin may be encountered while burring off the end plate. On the other hand, the inferior post is placed 5 mm below the caudal level’s superior end plate. This is because the caudal end plate does not require much bone removal. Further, a pin placed too caudally and not angled cranially can perforate the adjacent disc space. As far as the direction of the pins, the cranial angulation of the Caspar pins should be parallel to the disc space 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. If the localizing radiographs show that the patient is in perfect alignment, the pins are placed parallel to each other. If the patient is hypolordotic, then the Caspar pins can be inserted with the tips diverging to allow for lordosis. If they are hyperlordotic, then the pins are placed with the tips converging. Next, the pins must both be centered medial-laterally, because 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. Finally, placing the pins off to one side can compromise the fixation of the plate, as the hole for the pin may interfere with the ideal placement of the screw. Excellent visualization of the bodies before placing the posts will help to avoid errors at this step. Centering with reference to the spine, based on the uncinates, is more reliable than centering with reference to the patient’s chin and sternal notch. We therefore use the electrocautery to identify the curved lateral borders of the uncinates prior to placing the pins. If the lateral border of the uncinate is still not clearly identifiable, we place a Penfield 4 lateral to the uncinate to clearly identify it. 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 myelopathic or stenotic.

Discectomy.

There are two possible dangers in cutting the disc with a blade. The first is that a blade that is placed too deep can cut the dura and spinal cord. The second is that a blade that cuts lateral to the uncinate can cut the vertebral artery. The technique described here helps to prevent both complications. A #15 blade is used to cut the width of the ventral annulus. Do not insert the blade any deeper than the length of the sharp portion of the blade, which measures exactly 11 mm. This makes it unlikely for one to inadvertently incise the dura or cord. To prevent inadvertent injury to the vertebral artery, we start with the caudal end plate as far as possible on the side contralateral to the surgeon and use an up-and-down seesaw motion to incise the disc. As the knife blade approaches the ipsilateral side, it follows the curve of the ipsilateral uncinate until it hits the superior end plate. Then, we backhand the blade, cut away from the ipsilateral uncinate, and cut approximately half of the superior end plate ( Fig. 71-2A ). We do not go farther, as one can inadvertently go past the uncinate and cut the vertebral artery. Instead, we withdraw the blade and start again at the original starting point at the contralateral uncinate. But this time, the blade faces the contralateral side and is used to cut along the curve of the contralateral uncinate until it hits the superior end plate. Then we cut the disc off of the superior end plate toward the surgeon until we meet the halfway point where the previous cut had been made ( Fig. 71-2B ). A pituitary rongeur is used to remove initial disc fragments. The Caspar retraction can be increased once the ventral annulus has been excised. A curette (Codman Microsect 5B) can be held like a dagger while the shaft is stabilized with the other hand while scraping the disc thoroughly. The nondominant hand that is holding the shaft should be resting on the patient with all maneuvers to provide stabilization and control and prevent inadvertent injury to the cord. A side-to-side motion is safe as far lateral as the uncovertebral joint allows. Scraping too vigorously along the superior end plate can cause the curette to go laterally to the disc space and injure the artery. To prevent this, one should (1) not overdistract the disc space, (2) use a large curette that will not fit through the space between the end plates, and (3) scrape from lateral to medial at the uncinate region. The uncinates are thoroughly cleaned out by pointing the curette caudally and laterally and scraping from a dorsal to ventral direction. Do not use a large curette to remove the posterior annulus as it can inadvertently plunge too deeply and injure the cord. Instead, switch to a 2- or 3-mm curette.