Posterior Approach to the Subaxial Cervical Spine
Posterior Approach to the Subaxial Cervical Spine
The midline posterior approach is the most commonly used approach to the cervical spine, allowing quick and safe access to the posterior elements of the entire cervical spine. It is used for the following:
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Enlargement of spinal canal (laminectomy or laminoplasty)
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Treatment of tumors
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Nerve root exploration
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Excision of some herniated discs
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Open reduction and internal fixation of cervical spine fractures/dislocations
Position of the Patient
Place the patient in the prone position. Move the head into a few degrees of flexion to open the interspinous spaces. Tongs and a fixed brace are applied (Mayfield tongs or similar). This allows for careful control of the head and neck position during the procedure, minimizes the possibility of ocular pressure, and gives good access by the anesthetist to the airway (Fig. 6-50).
Alternatively, the patient may be seated upright, with the head held in a special brace. This position has the advantage of decreasing venous bleeding, but it has been implicated as a cause of air emboli.
Illumination is important; a cold-light headlamp or microscope use adds significant clarity to the operative field.
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Figure 6-50 The position of the patient for the posterior approach to the cervical spine.
Landmarks and Incision
Landmarks
The spinous processes are the most prominent landmarks in the vertebral arch. The C2 spinous process is one of the largest cervical spinous processes, as are C7 and T1. All three are quite palpable along the midline. Because it sometimes is difficult to distinguish between C7 and T1 during surgery, place a radiopaque marker (such as a needle) into the spinous process at the level of the pathology before making the incision, so that the exact location of the process can be identified. Sometimes placing a second marker into C7 may be helpful. Because the distance between the various cervical facet joints and interspaces is tiny, a significant portion of the neck may be dissected unnecessarily unless the vertebra being treated is identified, with the help of an x-ray film.
Incision
Make a straight incision in the midline of the neck (Fig. 6-51). Use the needle that has been inserted into the spinous process as a guide to and center point of the incision. Note that the skin of the posterior cervical spine is thicker and less mobile than the skin of the anterior neck, and that the resultant scar usually is broader; however, hair usually covers most of the scar.
Internervous Plane
The internervous plane is in the midline, between the left and right paracervical muscles (which are supplied segmentally by the left and right posterior rami of the cervical nerves).
Superficial Surgical Dissection
Continue the incision down to the spinous processes. Minimal bleeding may come from venous plexuses that cross the midline; these should be cauterized (Figs. 6-52 and 6-53).
Remove the paraspinal muscles subperiosteally from the posterior aspect of the cervical spine either unilaterally or bilaterally, depending on the exposure needed; bilateral removal is done for spinal fusion and unilateral removal for a herniated disc. Use a Cobb elevator or cautery, which can remove the muscles from the bone without damaging them unduly (Fig. 6-54). Carry the dissection as far laterally as necessary to reveal the lamina and the facet joints (Figs. 6-55 and 6-56). If necessary, cauterize the segmental arterial vessel that runs between the facets.
This dissection is quite safe. If the original muscular incision is not in the midline and cuts into muscles, however, notable bleeding can occur that will require immediate cauterization. If the patient has significant spina bifida, it is possible to enter the spinal canal, injuring neural tissue.
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Figure 6-51 Make a straight incision in the midline of the neck, centering the incision over the area of pathology.
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Figure 6-52 Retract the skin flaps and incise the fascia in the midline. Note the position of the third occipital nerve.
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Figure 6-53 Continue the dissection down to the spinous processes through the nuchal ligament.
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Figure 6-54 Remove the paraspinal muscles subperiosteally from the posterior aspect of the cervical spine either unilaterally or bilaterally, depending on the exposure needed. Note that the vertebral artery is considerably anterior to the posterior facet joints.
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Figure 6-55 Bilateral exposure of the posterior cervical spine.
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Figure 6-56 With a high-speed tool, then a small Kerrison rongeur, the caudal aspect of the lamina above, the rostral aspect of the lamina below, and the medial facet are removed.
Deep Surgical Dissection
Identify the ligamentum flavum that runs between the laminae. With a sharp blade, remove it from the leading edge of the lamina of the inferior vertebra. Place a flat, spatula-shaped instrument in the midline in the space between the two ligaments and cut down on the ligamentum flavum, with
the metallic unit separating the ligamentum from the underlying dura. Perform a laminectomy, either partial or complete, removing as much of the lamina as necessary to see the blue-white dura, which lies immediately below it, probably covered by epidural fat. Identify the posterior portion of the vertebral body, the disc space, and the possibly herniated disc (Figs. 6-57 and 6-58). Occasionally, the thin epidural veins surrounding the cord may bleed significantly. The veins can bleed anywhere; they are hardest to control between the anterior aspect of the cord and the posterior part of the vertebral body.
Dang
Nerves
Take care never to retract the exposed spinal cord and its nerve root overzealously. If enough bone is removed during the laminectomy, both medially and laterally, the exposure should be large enough to minimize the need for cord retraction. The nerve roots themselves should be retracted gently to prevent unnecessary tethering from postoperative adhesions. Occasionally, the facet joint must be removed partially to expose the nerve root.
The posterior primary rami of the cervical nerves supply the paraspinal muscles and sensation to the overlying skin; they rarely are in danger. Even if a posterior ramus must be cauterized, the nerve supply to the paracervical muscles and skin is so rich that the denervation has no clinical effect.
Vessels
The venous plexus in the cervical canal is plentiful and thin-walled; when it is retracted, it may bleed profusely. Frequently, bipolar (or Malis) cauterization is the best way to control the venous bleeding.
The segmental blood supply to the paracervical muscles may be cut or stretched as the muscles are stripped past the facet joints. The muscles often contract, stopping the small amount of hemorrhage; however, if the torn vessels can be seen, they should be cauterized. The blood supply to the posterior cervical muscles is generous. Cauterization causes no problem and allows for a dry surgical field. Occasionally, a nutrient foramen of the spinous processes or lamina may bleed. This can be controlled easily with a dab of bone wax or cautery placed directly against the foramen.
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Figure 6-57 Perform a laminectomy, partial or complete, removing as much lamina as needed. Gently retract the nerve root medially to identify the posterior portion of the vertebral body.
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Figure 6-58 Identify the disc space and a possible herniated disc.
The vertebral artery is enclosed in a bony canal running through the transverse process (transverse foramen). It is protected even when the dissection is directly onto the transverse processes. If the process is destroyed as a result of infection, tumor, or trauma, however, take great care not to enter the transverse foramen (see Figs. 6-54 and 6-62).
How to Enlarge the Approach
Local Measures
To enlarge the exposure, lengthen the skin incision. In addition, an extra vertebra may have to be dissected out proximally or distally. The exposure may be expanded laterally by drawing the muscles well out and past the facet joints and onto the transverse processes without causing damage, except at C1 and C2. On occasion, the laminae even may be exposed bilaterally and the laminectomy extended both proximally and distally to improve exposure to the spinal cord and nerves.
Extensile Measures
The cervical midline incision is very extensile. It may be extended proximally (staying in the midline plane) as high as the occiput of the skull and as far distally as the coccyx via subperiosteal removal of the paraspinal muscles.