Cervical Decompression, Instrumented Fusion, Arthroplasty, and Laminoplasty

Jad G. Khalil

Jeffrey S. Fischgrund

Cervical spinal stenosis results in compression of neural elements by anterior structures, posterior structures, or a combination of both. It can manifest as central canal stenosis resulting in global myelopathic symptoms, or foraminal stenosis that causes a more distinct picture of radiculopathy. Decompression is the mainstay of treatment of cervical stenosis. Reconstruction is often necessary after decompression; the method of reconstruction chosen depends on the offending mechanism, extent of the decompression, anatomic factors, and surgeon expertise. This chapter will review the various indications and techniques pertaining to cervical decompression and will cover the most commonly used techniques of reconstruction.

Anterior Cervical Discectomy and Fusion

Cervical radiculopathy often arises from compression by anterior structures and as such is adequately addressed by an anterior surgical approach. The common culprits causing nerve root compression are:

Herniated nucleus pulposus (HNP) that impinges on the exiting nerve root in the foramen (Fig. 30.1A).
Uncovertebral osteophytes with surrounding ligamentous structures cause impingement on the exiting nerve root just proximal to or in the neural foramen (Fig. 30.1B).
Disk height loss due to aging and degenerative disease produces stenosis owing to decreased foraminal height and causes the superior articular process to cause direct compression on the exiting nerve root.

Regardless of the exact anatomic location of the compression, symptoms are typically limited to a given dermatomal distribution and physical examination findings typically point to a defined root level. Although patients may also have concomitant axial neck pain, surgery is most effective for relief of the radicular complaints, relief of axial complaints being less predictable.

It is important, however, to have an exact understanding of the anatomy of the specific stenotic area in order to achieve a full and meaningful decompression of the involved neural elements.

Anterior cervical discectomy and fusion (ACDF) is the most commonly performed operation to achieve decompression of anterior offending structures. This procedure has several advantages making it the “gold standard” procedure for the most common types of pathology that result in cervical radiculopathy. In addition to the high clinical success rate and low morbidity of the procedure, ACDF allows effective decompression, both through direct nerve decompression and indirect foraminal enlargement. Direct decompression is generally performed by removing the offending structure such as HNP, osteophyte resection, and posterior longitudinal ligament (PLL) resection. Indirect decompression is effected through graft placement in the intervertebral disk space, which increases foraminal height, further aiding the decompressive efforts.

Figure 30.1 A: Posterolateral soft disk herniation (black arrow) causing impingement on the exiting C7 nerve root as it enters the C6–C7 foramen. B: Sagittal section showing compression of the C7 root by a disk osteophyte complex (white arrow).

Technique of Anterior Cervical Discectomy and Fusion

Positioning and Equipment

ACDF is performed in the supine position. Different tables can be used but we prefer to use the standard operating table placed “upside-down,” that is, with the longer end placed at the head to allow for AP and lateral fluoroscopic visualization. We place a small rolled towel in the interscapular area to prevent cervical kyphosis and allow an easier exposure to the anterior cervical area. The head is placed on a gel doughnut. We prefer to leave the patient’s head free and as such avoid taping or securing the head in a more rigid apparatus. The arms, elbows, and hands are extensively padded and tucked at the side of the patient. While gentle traction is exerted on both arms to depress the shoulders (aiding visualization for lateral radiography), we generally avoid taping the shoulders down to avoid issues related to neurapraxia of the cervical or brachial plexus.

Several pieces of equipment can improve the ease of performing ACDF and help in obtaining a superior decompression. A high-speed bur is used to remove the posterior osteophytes and help in uncinate resection. Microcurettes are used to complete the osteophyte resection, dissect the PLL, and decompress the foramen laterally. We recommend the use of a self-retaining retractor with an assorted blade system and an intervertebral disk spreader or a self-retaining vertebral body spreader (Caspar pins system). High-magnification loupes and a good illumination system or an operating microscope can be used. The advantage of the operating microscope is increased magnification and the ability of the assistant to view the same field as the surgeon; this can be important when operating with a trainee. However, the price of a good quality microscope can be a deterrent for some institutions and we find that using high-magnification surgical telescopes (at least 3.5x) associated with a headlight system results in excellent visualization as well.

Exposure

The exposure for the ACDF procedure is covered elsewhere in this text, however, some salient points pertaining to decompression are worth mentioning here. We generally prefer a transverse skin incision along the skin crease following Langer lines. The location of the incision is determined according to surface landmarks (hyoid bone, thyroid, and cricoid cartilage). The incision starts just lateral to the midline and stops at the medial border of the sternocleidomastoid muscle; the length of the incision measures generally about two fingerbreadths. For multilevel decompressions we also use a transverse incision but increase the length to about three fingerbreadths or even longer. It is important to note that when performing a larger incision, more exposure can be obtained by extending the incision more medially up to midline or just medial to the midline of the neck. Little added exposure is obtained by extending the incision more lateral than the medial border of the sternocleidomastoid. We prefer a transverse platysma split although a longitudinal or oblique cut in the platysma also results in satisfactory exposure. For multilevel surgery, we raise
generous subplatysmal flaps in the loose connective tissue layer just deep to the muscle fibers. The greater the number of levels to be addressed, the bigger the flaps made. Generally, this technique allows us to easily access C2 down to T1 or even T2 by using a transverse skin incision. Of course, an oblique skin incision can also be used for multilevel surgery but the cosmetic advantage of the transverse incision makes it our preferred type. The rest of the dissection and identification of the vertebral levels follows standard approach. We prefer the use of a localizing “protected” needle in the vertebral body to avoid the inadvertent violation of a normal disk level (and possible iatrogenic disk damage). Alternatively, a less invasive means of localization can be achieved by placing a small clamp on the longus colli adjacent to the disk level.

Technique for Anterior Discectomy

The disk is incised with a no. 15 blade and a rectangular annulotomy is performed followed by disk material removal with pituitary rongeurs and large curettes. We resect the anterior osteophytes with a Leksell rongeur and the osteophyte “lip” on the inferior aspect of the cephalad vertebra with a 3-mm Kerrison rongeur. Following that, we use a small Cobb elevator along the end plate to quickly remove the cartilaginous portion. This key step allows a rapid and homogeneous cartilaginous end plate removal and diminishes the risk of gouging the end plate. The high-speed bur is then used to remove the medial aspect of each uncinate process (Fig. 30.2). We recommend resecting the medial one-half of each uncus to facilitate access to the foramen and increase the space available for the graft. In cases of severe foraminal stenosis, we resect the posterior aspect uncinate process on the side of the pathology. Care must be taken to not extend the working area beyond the lateral border of the uncinate process and thus endangering the vertebral artery. A Penfield dissector can be placed lateral to the vertebral body and held by the assistant to offer protection. The posterior osteophytes should also be resected and this is performed using a combination of high-speed drill and microcurettes.

Figure 30.2 Pictorial depicting the normal upslope of the uncinate processes. The medial one-half of the uncinate process is usually resected (gray area); this allows better visualization of the nerve root as it exits the foramen. It also allows “squaring” of the disk space providing space for a bigger graft and improving end plate contact.

Technique for Anterior Foraminotomy

When adequate exposure of the posterior aspect of the uncinate process is obtained, a small microcurette can be inserted just posterior to the uncus to create a plane. The rest of the foraminotomy is performed using a high-speed bur and a 2-mm Kerrison rongeur until a nerve hook can be easily passed into the foramen. At this stage, the exiting nerve root should be visualized. It is important that any instrument be passed into the foramen under direct vision of the root to prevent iatrogenic injury to the nerve root sleeve. In cases where there is a question as to whether the decompression has been carried laterally enough, a small nerve probe can be passed into the foramen angling the hood caudad. The pedicle of the caudal vertebra can then be palpated. It is generally accepted that if the foramen is free as far laterally as the pedicle then the decompression is complete.

At this stage, any extruded disk material can be probed and removed from the foramen and decision should be made whether resection of the PLL is indicated.

Posterior Longitudinal Ligament Resection

We generally recommend resecting the PLL for most cases. This has several advantages:

The PLL itself can be an offending structure and causing stenosis.
Extruded disk material can be lodged and thus “hiding” posterior to the PLL fibers.
In cases of severe disk collapse, the PLL fibers may be taut and can prevent adequate height restoration by the intervertebral graft.

In order to facilitate PLL resection, microcurettes are used to create a fenestration in between the fibers. A 2-mm Kerrison is then advanced in this window and the PLL can then be easily resected by taking alternating caudad and cephalad bites of ligament along with some posterior osteophyte bone. We highly recommend using high-powered loupes or use of the operating microscope for this portion of the procedure. Once the posterior osteophytes and PLL are resected, an excellent view of the ventral aspect of the thecal sac is then possible. Any remaining soft tissue or bony material can be removed leading to full anterior decompression of the neural elements.

Anterior Cervical Arthrodesis

Once the decompression is complete, anterior reconstruction is begun. Anterior arthrodesis is the most
commonly performed procedure and still considered the gold standard after discectomy. Historically, anterior arthrodesis has been performed using autologous tricortical iliac crest bone graft without instrumentation. Limitations of this procedure include donor-site morbidity and the need for postoperative bracing until healing is complete. To circumvent these shortcomings, anterior instrumentation has been developed leading to multiple options that are available and accepted in today’s practice. Fusion rates between the use of autograft or allograft with plate and screw fixation have been reported to be equivalent.

Anterior Spacer Options

The main grafting options currently available include allograft-machined structural bone and synthetic spacers. Spacers can be made of metal (titanium) or various other materials, polyetheretherketone (PEEK) being one of the most common (Fig. 30.3). In choosing the appropriate spacer material, several attributes should be kept in mind:

There should be a hollow region where sufficient grafting material can be packed.
The modulus of elasticity of the graft should be close to that of the native cortical bone, to minimize end plate subsidence or spacer breakage.
Spacers should have ridges to achieve an initial high-friction contact with the end plates.
Spacers should have initial stiffness to withstand initial forces across the intervertebral joint until the fusion is complete.

Although various prosthetic materials carry different biomechanical as well as ingrowth advantages, we prefer the use of PEEK spacers due to availability, low cost, and radiolucency, which allows judging the adequacy of the fusion mass on subsequent radiographs.

Both spacers and machined allografts generally have a hollow area into which bone graft or bone substitute can be packed. There are different options available on the market for this use. We prefer the use of the autologous bone harvested from osteophytes combined with a small amount (0.5 cc) of demineralized bone matrix.

Figure 30.3 PEEK cages are manufactured with different sizes and heights; note large space available for bone grafting (white arrows) and ridges to increase friction with end plate and provide immediate stability (black arrows).

Anterior Instrumentation

Anterior plate instrumentation has been used to increase fusion rates, provide immediate postoperative stability, and to decrease the risk of graft subsidence. When using autograft structural bone at a single level, the use of instrumentation has not been shown to affect fusion rates but it was reported to decrease the risk of graft collapse. At 2 or more levels, plate instrumentation decreases the pseudarthrosis rate and thus is considered standard procedure for multilevel ACDF. The advent of locking screw constructs obviates the need for bicortical screw fixation and thus enhances the safety of screw placement. It is recommended to keep the edge of the plate at least 5 mm away from the adjacent disk level (Fig. 30.4). We recommend the use of titanium plate and screw system and routinely use unicortical screw fixation; bicortical screw fixation can still be used, especially in cases where screw purchase is suboptimal. There is no clear evidence whether coronal alignment of the plate impacts the clinical outcome. It is our routine practice, however, to place temporary fixation pins and check anteroposterior and lateral radiographs before placing the definitive screws. We generally use self-tapping screws and thus a tap is not used as an extra step between drilling and screw placement.

Stand-alone Cervical Spacer Devices

As an alternative to plate and screw fixation, there are available intervertebral spacers with built-in fixation devices. These include screws or fins that provide anchoring of the spacer in the vertebral bodies. Some biomechanical studies concluded that stand-alone fixation offers equivalent stability to plate and screw design; others demonstrated that they offer inferior biomechanical stability. Although the clinical significance of this comparison remains unclear, we continue to recommend the use of anterior plate fixation for de novo cases. Stand-alone cage and screw devices can however be very valuable in revision cases where plate removal can be challenging, especially after prior multilevel fusion (Fig. 30.5).

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