Cervical Arthrodesis Technique

Updated: Mar 19, 2015
  • Author: Lawrence S Chin, MD, FACS; Chief Editor: Jorge E Alvernia, MD  more...
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Technique

Approach Considerations

The debate regarding the anterior versus the posterior approach remains a hot topic. Although the literature supports the successful management of several cervical spinal conditions using either approach, it seems logical to approach the cervical spine from the direction where the majority of the pathology is. One issue to keep in mind when considering these two approaches is that anterior decompression usually involves fusion, whereas posterior decompression may not. [6]

An important question to be addressed when considering an anterior versus a posterior approach to the cervical spine is whether there is spinal instability. White and Panjabi [7] defined spinal stability as the ability of the spinal column to tolerate physiologic loads without initial or additional neurologic deficit, incapacitating pain, or major spinal deformity. Several methods exist to identify and quantify cervical spinal instability. White and Panjabi proposed a point system to predict subaxial cervical spinal instability based on the radiographic appearance and the presence or absence of neurologic deficits. [7]

The 3-column classification system developed by Denis [8] for thoracolumbar fractures is also often used to assess cervical spine injuries. In clinical practice, cervical spinal instability can be evaluated using static radiography, such as CT scanning, MRI, and plain radiography, and dynamic studies, including flexion-extension plain films, fluoroscopy, and MRI.

The anterior approach to the subaxial cervical spine can include simple discectomy procedures without grafting material, fusion procedures with grafting material, and fusion and internal fixation procedures with grafting material augmented with a screw-plate system. Several cervical screw-plate systems are available. The decision to use one fixation system over another is mainly based on the surgeon’s preference and familiarity with the system.

Use of these screw-plate systems for fixation has been reported to be associated with improved fusion rates, earlier return to work, and decreased postoperative discomfort than anterior procedures without internal fixation. [9, 10, 11, 12, 13, 14] However, performing discectomies with or without fusion but absent internal fixation can be considered for patients with a normal preoperative cervical lordosis who have one-level or two-level spondylotic disease.

The posterior approach to the subaxial cervical spine predates the anterior approach. The earliest posterior subaxial cervical spine fusion procedures used autogenous bone grafts for fusion; however, these constructs conferred little stability to the spine, which resulted in prolonged bed rest, cervical traction, and use of external orthoses while awaiting bony fusion to occur.

Internal spinal fixation of the posterior cervical spine was first described by Hadra, [15] who, in 1891, used wire to secure adjacent unstable cervical vertebrae in trauma patients and those with Pott disease. As a result, several posterior fusion techniques were developed that incorporated wire, interlaminar clamps, and screws and rods for stabilizing the spine posteriorly. Such implants have minimized or eliminated the need for postoperative external immobilization, thus enhancing patient comfort and enabling early mobilization and rehabilitation.

Advantages for the anterior approach include familiarity with the approach for the surgeon, as well as less postoperative discomfort and pain for the patient. However, the anterior approach potentially risks the anterior vasculature and visceral structures, as well as the recurrent laryngeal nerve. This approach also usually requires fusion.

An advantage of the posterior approach is that it is well known by spinal surgeons. The posterior approach avoids the potential risk to anterior vasculature and visceral structures and provides better resistance to rotational forces. However, with the posterior approach, there is greater postoperative discomfort and pain, longer hospital stays, and a potential risk to vertebral arteries and neural structures.

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Anterior Approach

Patient preparation

It is important to avoid spinal cord injury during intubation due to cervical spine extension, especially in patients with cervical spinal myelopathy and/or unstable cervical spinal fractures. In such patients, fiberoptic awake intubation may be considered.

The patient is first positioned supine on the operating table. When intraoperative neuromonitoring is being used, electrodes are placed and secured appropriately. A bladder Foley catheter might be considered and inserted. Sequential compression devices are used to decrease the risk of deep venous thrombosis.

The patient’s hips and knees can be slightly flexed by placing soft pillows underneath the knees to prevent stretch injuries. The patient’s elbows, wrists, and ankles should be appropriately padded, and the patient should be secured to the table using safety straps or belts. In addition, the patient’s shoulders can be taped down to place some mild traction on the shoulders and security to the table, facilitating visualization of the cervical spine during fluoroscopy imaging, especially for the lower cervical spine levels. It is important to avoid excessive traction of the shoulders to avoid brachial plexus stretch injuries. Lastly, a folded towel is placed under the patient’s neck to provide support during anterior pressure from graft impaction and screw placement.

Surgical technique

The surgery can be performed using a right-sided or a left-sided approach. There are several reasons for choosing to operate from the right or the left side of the patient. In general, right-handed surgeons tend to perform the approach from the right side, whereas left-handed surgeons perform the surgery from the left side. In addition, while the right-sided approach increases the susceptibility of recurrent laryngeal nerve injury owing to its variable course on the right side, the thoracic duct is susceptible to injury only from the left-sided approach.

With either the right-sided or left-sided approach, a natural skin crease can be used for the incision, which will result in a more cosmetically satisfactory outcome. For one-level and two-level disks, a horizontal incision can be used. For three-level disks, a carotid longitudinal incision along the anterior border of the sternocleidomastoid muscle might be considered. While anatomical landmarks can be used to determine the level of the incision on the neck, many surgeons use intraoperative fluoroscopy to verify the level of the incision.

Once the site of the incision is marked, the patient is prepared and draped in a standard fashion. Subsequently, a timeout will be performed for verification. The marked incision can be infiltrated with local anesthetic prior to the skin incision.

It is important to understand the different fascial planes in the neck for optimal dissection and exposure. The superficial layer can be opened, and platysma muscle can be incised. Next, a subplatysmal release is performed. Then, the superficial cervical fascia can be opened and released to expose the sternocleidomastoid muscle. The middle cervical fascia envelops the omohyoid muscle. Release of this fascial layer and retraction are usually adequate to mobilize the omohyoid muscle. However, on some occasions, the muscle needs to be transected to provide better exposure.

In addition to the omohyoid muscle, the trachea and esophagus are also invested in this middle fascial layer and can gently be retracted medially. The carotid artery should be protected and retracted laterally to allow for further dissection down to the deep cervical fascia, which separates the vertebral bodies and longus coli muscles from the trachea and esophagus.

The longus coli muscles are then released laterally to provide better exposure to the vertebral bodies and intervertebral discs. The longus coli muscles are useful to determine the midline since they are located equidistant from this point. In addition, they can serve as anchors to hold the self-retaining retractors in place.

Once exposure is achieved, it is important to confirm the level of the surgery radiographically. While some surgeons use a spinal needle and insert it in the intervertebral disk of interest for localization, an alternative is to use a small hemostat clamp to pinch either longus coli muscle at the level of the disk of interest to avoid injury to an otherwise nonsurgical healthy disk. The localization image obtained is then reviewed to confirm the correct surgical level and a second time-out performed for verification.

Once the self-retaining retractors are in place at the level of the surgical disk, distraction-post pins are then placed and centered in the vertebral bodies above and below the disk. The distraction-post pins are then used to gently distract the disk space after the anterior longitudinal ligament is incised. Some surgeons operate using headlight illumination and loupe magnification; alternatively, the surgical microscope can be used to provide illumination and magnification. In addition, the attached camera and extra viewing heads of the microscope provide an opportunity for the surgical team to follow the various stages of the operation and serve as a teaching tool for surgical residents and students.

Different tools and instruments, such as a curette and a Kerrison rongeur, can be used to remove the disk material. Alternatively, a high-speed drill can be used for the discectomy portion of the procedure. The discectomy should be carried out until the posterior longitudinal ligament (PLL) is visualized. Controversy exists with regard to incising the PLL because of concern that this might worsen spinal instability, but removal is generally indicated to ensure adequate cord decompression and to avoid missing a subligamentous disc fragment.

Decompression is considered complete when the neural foramina are open bilaterally. This can be tested with a small blunt probe that should pass easily into each foramen when adequately decompressed. Care should be exercised when decompressing laterally to avoid injury to the nearby vertebral arteries. From a right-sided approach, it is easier to open the left foramen and vice versa. When opening the ipsilateral foramen, an adequate lateral discectomy is critical to provide an unobstructed view of the foraminotomy.

After completion of the discectomy portion of the procedure, the fusion interbody graft is prepared. In addition to facilitating fusion, interbody grafting also restores the disk height and increases the opening of the neural foramina. Interbody grafting can be performed using bank bone or autograft harvested from a donor site. Alternatively, the use of synthetic materials such as carbon fiber cages is gaining more acceptance. The major concern with an autograft is donor site complication and pain, while viral or prion transmission is the main risk associated with bank bone. Importantly, most spinal surgeons feel that autograft is the criterion standard. Nonetheless, several reports in the literature have sown fusion rates with banked bone that are comparable to autograft.

The above steps can be repeated for any additional disk during a multilevel procedure. Once all of the interbody grafts are in place, the distraction-post pins are removed. Any bleeding from the sites of the pins can be stopped with bone wax. An internal fixation screw-plate system is then placed. Several screw-plate systems exist on the commercial market. The plate is positioned and centered over the vertebral bodies and interbody graft construct(s) and then secured in place using screws that are inserted into the vertebral bodies. Both plate length and screw length and width are important, but bicortical screw purchase is not required, as all modern systems have a locking mechanism to prevent screws from backing out. The edge of the plate should not overlap the adjacent disc space.

Before closing the surgical wound, fluoroscopic images can be obtained in the anteroposterior and lateral views to ensure good placement of the interbody grafts, as well as the internal fixation system. The surgical wound is thoroughly inspected and meticulous hemostasis must be ensured prior to wound closure. The wound is then closed in standard multilayer fashion before a sterile dressing is applied over the surgical wound.

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Posterior Approach

Patient preparation

The nature of induction and intubation largely depends on the cervical pathology at hand. With unstable cervical spine injuries, the patient’s cervical spine should be immobilized in a cervical collar, halo, or cervical traction. Neutral alignment of the cervical spine must be maintained during intubation, and, after the patient is intubated, neuromonitoring electrodes can be placed and secured appropriately.

A bladder Foley catheter can be inserted, and sequential compression devices are used on the legs to decrease the risk of deep venous thrombosis. The patient is then transferred to the operating table, while maintaining neutral cervical alignment and then positioned prone. Prepositioning and postpositioning neuromonitoring is recommended to rule out positional changes and/or to correct a surgical positioning that may be the cause of those changes.

Once on the operation table, the patient’s neutral cervical alignment is maintained using a 3-point Mayfield head-holder or a halo apparatus that is secured to the operating table. The patient is placed on chest rolls or other positioning frames on the table to decrease abdominal pressure, minimizing intraoperative bleeding. In addition, the foot of the table should be slightly elevated to promote venous return from the lower extremities.

The patient’s arms are tucked in to the sides, and the wrists, elbows, knees and feet appropriately are padded. The patient’s body is secured to the operation table using safety straps or belts. An intraoperative fluoroscopy image is then obtained to confirm neutral alignment of the spine and can also serve for localization of the spine level.

Surgical technique

Once the correct level is determined on fluoroscopic imaging, the patient is prepared and draped in a standard fashion. A time-out should then be performed for procedure verification. Subsequently, local anesthetic can be infiltrated along a premarked midline incision. The incision is made in the midline, and Bovie electrocautery is used to perform a subperiosteal dissection to expose the spinous processes and lamina.

For lateral mass screw placement, it is important to carry the dissection laterally to expose the facet joints and the lateral borders of the lateral masses. Caution must be exercised in keeping the integrity of the facet joints above and below the involved segments to prevent any unwanted instability or fusion at these levels.

If the procedure also involves a laminectomy, the lateral mass screw sites are marked, drilled, and tapped prior to performing the laminectomy. This technique will protect the dura and the spinal cord from injury during the instrumentation portion of the procedure. The entry point of the lateral mass screw is marked approximately 1 mm medial to the center of the lateral mass. Then, the outer cortex is pierced using a high-speed drill or an awl.

Next, the drill is used to create the hole and is advanced to the appropriate depth to accommodate the length of the screw, which can be determined preoperatively on a CT scan. The trajectory used for drilling the hole is approximately 15-20° superior and 30° lateral. This trajectory will decrease the risk of injury to the nearby vertebral arteries and nerve roots. After drilling the hole, the dorsal cortex of the hole can be tapped with a cancellous tap.

Once all the screw holes are prepared, the laminectomy can be performed, taking care to save removed bone for use as autogenous bone graft for fusion. After the completion of the laminectomy, the screws are placed, and a pair of rods are then bent and contoured to the lordosis of the cervical spine. The rods are set on the screws heads and secured using a locking-cap mechanism. The facet joint is decorticated using a high-speed drill, and harvested autogenous bone graft can then be packed into the decorticated facets.

It is worth noting that either a pedicle or a lateral mass screw can be used at C7. The C7 lateral mass is thinner than the rostral cervical lateral masses. In addition, the vertebral arteries do not usually pass through the foramen transversarium of C7; therefore, placement of pedicle screws at C7 is safe. In this circumstance, the drill is angled 25-30° medially and perpendicularly to the rostral-caudal plane.

The surgical wound is irrigated and hemostasis obtained. A medium-sized Hemovac drain is placed below the fascia layer, and the wound is closed in a standard multilayer fashion with the skin edges reapproximated using staples or a running suture. Finally, a sterile dressing is applied over the surgical wound.

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