Anterior Cervical Discectomy and Fusion

Indications

Indications for anterior cervical discectomy and fusion (ACDF) include compression of neural elements (causing radiculopathic or myelopathic signs and symptoms) due to degenerative disease, trauma, and infection at one or multiple cervical spine levels. It should be noted that ACDF may be combined with posterior fixation to restore cervical lordosis prior to posterior instrumentation during multi-level cervical fusion procedures.

The video clips below illustrate clinical signs of cervical myelopathy, as seen in a patient who is about to undergo ACDF.

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Preoperative Planning

Perform a thorough history and physical examination prior to surgical planning, including a detailed account of the patient’s symptomatology and signs of neurologic compromise. Laboratory tests (both chemical and hematological) may be suited to the patient’s history. X-rays of the cervical spine, including anteroposterior (AP), lateral, oblique, and dynamic lateral (flexion and extension views) should be obtained to examine bony anatomy prior to operative planning (Figure 1).

Figure 1. Lateral cervical spine X-ray demonstrating previous fusion at C5-7 and spondylotic changes at the remainder of the cervical spine

A computed tomography (CT) scan may be helpful to gain further appreciation of bony detail. In addition, magnetic resonance imaging (MRI) of the cervical spine should be obtained to examine the condition of the neural elements, as well as soft tissue and vascular anatomy (Figures 2-3). In particular, the level(s) and laterality of pathology should be noted, as well as vascular anomalies that may be encountered during the procedure.

Be sure to align patient symptoms and examination findings to pathology noted on radiologic studies. Failure to note correlation between the two may result in ineffective surgical intervention.

Figure 2. Sagittal T2-weighted MRI demonstrating previous fusion of C5-7 and disc herniations at C3-4 and C4-5

Figure 3. Axial T2-weighted MRI demonstrating a left-sided disc herniation at C3-4, compressing the left exiting nerve root

ACDF is employed from the C2-3 level to the C7-T1 level, with C5-6 and C4-5 being the most common. One- and two-level procedures are the norm, although fusion of three or four levels has been performed. A variety of interbody fusion options have been described, including iliac crest autograft or allograft, fibular allograft, and polyetheretherketone (PEEK) grafts. The decision to use instrumentation in conjunction with the application of an interbody fusion device is based on history and physical exam findings, as well as radiologic findings and surgeon preference. There are some data to suggest that instrumentation of the intended fused segments may lead to a higher rate of fusion, particularly with two or more levels. Instruments to have available include:

Self-retaining blade-type retractors
Kerrison rongeurs
Curettes
High-speed burr
Graft selection
Anterior cervical plating instrumentation, if desired

Spinal cord monitoring, including transcranial motor evoked and somatosensory evoked potential monitoring, is currently standard of care.

Positioning

The patient is positioned supine on the operating room table, and the head is supported with a round foam pillow or other supportive device. General endotracheal anesthesia is administered. A rolled sheet or saline bag wrapped in a surgical towel is positioned under the scapulae of the patient to ensure adequate neck extension for exposure of the cervical spine. The shoulders may be taped in caudal traction to further aid exposure. If in-line traction is required, Gardner-Wells tongs may be applied with the amount of traction determined at the surgeon’s discretion (Figure 4).

Figure 4. Clinical photograph demonstrating positioning in the supine position with patient intubated and Gardner-Wells tongs in place for cervical traction

Approach

Although several palpable landmarks are present to guide the level at which an incision is marked, we prefer the use of the image intensifier to locate and mark the levels of pathology on which we intend to operate (Figure 5). Choosing the side from which to approach the cervical spine is largely based on surgeon preference, though due to the less reliable path of the recurrent laryngeal nerve on the right, we prefer to approach the spine from the patient’s left side.

Figure 5. Localization of levels to be addressed demonstrated on lateral fluoroscopy prior to prepping and draping the patient

A transverse incision is preferred for cosmetic reasons, and if possible, the incision should be placed in the nearest skin crease. The incision is marked from the midline to the anterior border of the sternocleidomastoid muscle (Figure 6).

Figure 6. Draping complete and transverse left-sided incision marked at appropriate level

The operative field is prepped and draped in the normal sterile manner using an adhesive field drape. The skin is incised using a scalpel; the remainder of the dissection is carried out using electrocautery, dissecting scissors, and finger dissection. The superficial fascia and platsyma are incised inline with the skin incision (Figure 7).

Figure 7. Skin incision complete and platysmus exposed

The investing layer of deep cervical fascia is next encountered, and it is entered at the plane between the sternocleidomastoid muscle and the cervical strap muscles. Dividing this layer of fascia reveals the pretracheal layer of deep cervical fascia, which blends with the carotid sheath laterally and encloses the esophagus and trachea medially. Depending on the level of dissection, the omohyoid muscle may be encountered in the operative field; it may be carefully divided, erring toward the midline to prevent damage to the cervical plexus lateral to the carotid sheath. The pretracheal fascia is carefully divided using a combination of careful instrument dissection and finger dissection. Once the plane is developed between the carotid sheath laterally and the trachea and esophagus medially, the spine is reached, obscured by prevertebral fascia and longus colli muscles.

Note that the recurrent laryngeal nerve is located within the tracheoesophageal groove and take care to avoid injuring the nerve when entering the pretracheal fascia and during retractor placement.

Lateral self-retaining blade retractors are placed (Figure 8); depending on the surgeon’s preference and the number of levels exposed, cranial/caudal retractors may also be placed. There is some debate as to whether the endotracheal tube cuff ought to be deflated and reinflated at this phase of the operation to help prevent recurrent laryngeal nerve palsy; studies support both sides of the argument.

Figure 8. Self-retaining retractor (medial-lateral) in place

The prevertebral fascia is divided in the midline using rolled gauze (“peanuts”) in Kelly clamps. The longus colli is elevated subperiosteally on either side of the spine, taking care not to err anterior and lateral to the muscle mass so as to avoid damage to the sympathetic chains flanking the spine. Ebraheim et al demonstrated on cadaveric specimens that the sympathetic trunks are on average 10.6 mm from the medial border of longus colli muscles. Lateral exposure should be obtained to the uncus on either side of the caudal vertebral body.

At this point, the level(s) exposed should be confirmed radiographically. This is often accomplished using a bent spinal needle (Figure 9) placed in either the anterior annulus of the disc of the intended level of surgery or in the substance of the vertebral body itself.

Figure 9. Disc space marked with spinal needle before discectomy

If desired, the surgeon may choose to position an operating microscope at this time.

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Techniques

Once the appropriate levels have been identified, the annulus of the intervertebral disc is incised, with each lateral movement of the scalpel progressing toward the midline. The blade is directed from a caudal to cranial direction to remove a rectangular segment of annulus (Figure 10). The disc material is then removed using a combination of angled curettes and pituitary forceps (Figures 11-12). Further disc space preparation may be accomplished using rasps and/or a high-speed burr to remove all cartilaginous material. We prefer to use a high-speed burr to both remove osseous overhang from the cephalad vertebra and to produce a rectangular space in which to place the intervertebral device.

Figure 10. Performing the anulotomy at the operative disc space

Figure 11. Probe placed in disc space after partial discectomy complete

Figure 12. Exposure of the disc space after discectomy complete

The posterior longitudinal ligament (PLL) may be entered if necessary to address posterior pathology. Any posteriorly herniated or extruded disc fragments are removed using up-facing Kerrison rongeurs; this instrument may also be used to docompress neuroforaminal stenosis.

Once adequate decompression of neural elements has been achieved, trial intervertebral devices are used to choose an appropriately sized cage. We prefer to use cages with a lordotic shape to help restore normal cervical lordosis.

The correctly sized cage is then chosen and packed with autograft (local or iliac crest) or an allograft substitute. The cage is impacted into the intervertebral space so that the anterior surface of the cage is flush with the anterior surfaces of the cranial and caudal vertebrae. If the cage has a radiographic marker, the depth of the cage may also be assessed with lateral fluoroscopy. After satisfactory placement of the graft/cage, the weight may be removed from the Gardner-Wells tongs.

The plate to be used is then chosen. It should span the disc space with enough length to provide adequate purchase of bone for the screws used to affix the plate (Figures 13-15). Of note, Park et al demonstrated that ensuring at least 5 mm between plate margins and adjacent disc spaces was associated with a lower rate of adjacent segment ossification. The length of the screws is determined based on preoperative radiographs and the use of a depth gauge intraoperatively.

Figure 13. Instrumentation including anterior plate, screws, and screwdrivers

Figure 14. Placement of drill for advancement of screw through anterior plate; graft is visible between vertebrae

Figure 15. Final view of plate spanning C3 to C5

After satisfactory placement of the plate, hemostasis is attained, the wound is copiously irrigated, the retractors are removed, and the wound is closed in layers over a suction drain.

Pearls and Pitfalls

Review imaging studies carefully when considering a surgical indication and in the operative planning stage.

Aligning a patient’s complex of symptoms with imaging findings is of paramount importance in achieving a satisfactory result.

Understanding the anatomy of the patient by noting the course of the vertebral arteries, the bony architecture of the spine, and the areas of neural compression will ensure that problem areas are addressed while avoiding catastrophic complications.

Postoperative Care

Based on surgeon preference, the patient may or may not be placed in a cervical collar after the application of the dressing in the operating room.

The drain output should be monitored and the drain removed when the surgeon deems appropriate.

Neurologic examinations are performed the evening of the operation and for each subsequent day until the patient is discharged from the hospital, comparing the findings with the preoperative exam. If the patient remains in the hospital for more than 1 day postoperatively, we change the operative dressing and check the appearance of the wound.

The wound should remain dry for 7 days postoperatively, after which the patient may shower, allowing water to rinse over the wound; submerging the wound, however, should be avoided.

Our preference is to see the patient postoperatively at 2 and 6 weeks, 3 and 6 months, 1 year, and each year thereafter. We obtain X-rays at each postoperative visit. If there is any doubt as to the development of fusion, a non-contrast CT scan may be obtained to evaluate the presence of pseudarthrosis.

Outcome

Bohlman et al reported on 122 patients with cervical radiculopathy treated with ACDF using iliac crest autograft, with mean 6-year follow-up. At the last follow-up, 81 patients had no pain in the neck, 26 had mild pain in the neck, 9 had moderate pain in the neck, 4 had mild radicular pain, and 2 had a combination of mild radicular pain and moderate pain in the neck. One hundred and eight patients had no functional impairment, and 14 had a slight limitation of function during the activities of daily living. Pseudarthrosis was identified at 24 of 195 operatively treated levels. Sixteen patients who had a pseudarthrosis were symptomatic, with 4 having enough pain to justify revision. At the time of the most recent follow-up, 53 of the 55 patients who had had a motor deficit had experienced a complete recovery; the 2 remaining patients had a partial recovery. Seventy-one of the 77 patients who had had a sensory loss had regained sensation. None of the patients had an increased neurologic deficit postoperatively.

Peolsson and Peolsson evaluated 95 patients (mean 76 months follow-up) undergoing ACDF for cervical radiculopathy. They determined that the following were predictors of clinical success postoperatively:

Low-level preoperative pain intensity and disability (as determined by the Neck Disability Index or NDI)
Non-smoker
Male
Good hand strength
Active range of motion of the cervical spine in the sagittal and coronal planes

Of note, Peolsson and Peolsson found that radiologic findings (segmental height, segmental sagittal alignment) were not significant relating to long-term outcomes.

Anderson et al evaluated 486 patients as part of a retrospective cohort study using data from participants in randomized controlled trials examining outcomes following anterior cervical disc arthroplasty versus ACDF. They determined that pending litigation, workers’ compensation, and dermatomal sensory loss were negative predictors of outcome, while positive predictors identified were preoperative working status, high NDI score, and increased age.

Adjacent Segment Disease

Hilibrand et al reported a 2.9% per year incidence of the development of symptomatic adjacent segment cervical spine disease in patients who had undergone ACDF; the overall prevalence after 10 years was 25.6%. Partly due to the fact that they found a lower incidence of adjacent segment disease when more than one level was fused, the authors recommended that all symptomatic segments and segments demonstrating neural compression be incorporated into fusion constructs. The etiology of this degeneration is currently unknown, but is thought to be due to either normal progression of cervical spondylosis, alteration in cervical spine biomechanics following fusion, or both.

Kolstad et al studied 46 patients undergoing one-level ACDF without instrumentation. They obtained plain radiographs 1-year follow-up and then measured sagittal plane adjacent segmental motion (both cranial and caudal segments) preoperatively and at follow-up. The differences between preoperative and postoperative range of motion of adjacent segments were not statistically significant, leading the authors to conclude that they could not confirm the assumption that fusion of the cervical spine at one level induces increased motion in adjacent segments.

Pseudarthrosis

When performed with the use of a plate, ACDF has been shown to have a low rate of pseudarthrosis, although the rate increases as the number of levels fused increases. In a meta-analysis, Fraser and Hartl reported a fusion rate of 97.1% for a one-level fusion, 94.6% for two levels, and 82.5% for three levels. With an increase in the number of levels fused, the use of a plate becomes more significant, as the fusion rate for ACDF without use of plate for one-, two- and three levels was reported as 92.1%, 79.9%, and 65%, respectively.

Dysphagia

Some level of postoperative dysphagia has been reported to occur in between 28% and 57% of patients undergoing anterior cervical surgery. This has been suggested to occur from a combination of factors, including esophageal denervation, hardware prominence, soft tissue swelling, scar tissue formation and cervical hyperextension due to malpositioning in a hard cervical orthosis . Lee et al , in a prospective cohort study, followed patients for 2 years and found that the rate of dysphagia fell from 54% at 1 month to 13.6% at 24 months. They identified revision procedures and increasing number of levels involved at surgery as risk factors for the development of both short- and long-term dysphagia.

Complications

Vertebral Artery Injury

The incidence of vertebral artery injury during anterior cervical surgery has been reported to be around 0.3%. These injuries can be avoided by maintaining awareness of the midline of the spine, thereby preventing excessive or skewed removal of bone during corpectomy or disc space preparation. Additionally, preoperative MRI scans should be carefully reviewed to identify anomalies in the course of the vessels.

Should an injury occur, the longus colli must be further elevated and the artery exposed at the level of the transverse foramen. The bone overlying the artery may be removed using a 2-mm Kerrison rongeur. Once the artery is exposed, the decision of repair versus ligation must be addressed, with repair being the preferred management. If necessary, an intraoperative vascular surgery consult may be placed. If repair is not possible, ligation is performed.

It is worth noting that the rate of brain stem infarct resulting from from vertebral artery occlusion has been reported to be up to 3.8%.

Esophageal Injury

Esophageal injury may be caused by inappropriate retractor placement or damage caused by a surgical instrument such as the high-speed burr. The rate for this potentially devastating complication has been reported to be between 0.2% and 0.4%; if the injury is missed, the mortality rate has reached 50%.
In the event of injury, a thoracic or general surgery consult should be obtained for exploration during the surgery or postoperatively with the use of endoscopy. The incidence of this complication may be minimized by diligent use of an additional hand-held retractor by the assistant if the self-retaining retractors do not provide sufficient protection.

Spinal Cord Injury

Spinal cord injury has been reported to occur in 0.2 to 0.9% of patients undergoing anterior cervical spine surgery, and can be secondary to excessive extension of the cervical spine during patient positioning. Motor- and somatosensory-evoked potential monitoring are essential for providing feedback regarding the onset of neurologic injury.

Dural Perforation

Durotomy has been reported to occur at a rate of 3.7% during anterior cervical spine surgery, and it is associated with ossification of the posterior longitudinal ligament and revision surgery. Primary suture repair and seal with fibrin glue is the preferred method of addressing this complication, although materials for a dural patch should be available if deemed necessary.

Airway Compromise

Airway compromise has been reported to occur in 2.8% of patients following ACDF.

Suk et al reported on the amount of prevertebral soft tissue swelling seen on plain radiographs taken in the days following one- or two-level ACDF. They noted that increased swelling was associated with instrumentation above C5 and that swelling was most severe at postoperative days 2 and 3. However, they were not able to demonstrate a correlation between the amount of swelling and the incidence of airway compromise.

Other studies have demonstrated that smoking, asthma, prolonged operative time, obesity, transfusion requirement, and multi-level surgery or procedures involving C2 were linked to the development of significant postoperative prevertebral swelling. However, these studies did not examine whether this had a causative effect on the development of airway complications.

Of note, a recent randomized controlled trial by Lee et al found that the use of triamcinolone 40 mg applied to the retropharyngeal space after one- or two-level ACDF significantly reduced posterior soft-tissue swelling and odynophagia, without affecting the rate of fusion.

Dysphonia

Dysphonia, defined as a change in voice, taking the form of development of hoarseness to difficulty speaking, has been reported to occur in 2% to 30% of patients in the immediate postoperative period, while the rate of persistent vocal cord paralysis following anterior cervical surgery has been described as 0.33% to 2.5%.

There has been debate over the most effective method of minimizing this risk. Apfelbaum showed that pharyngeal tissue was put under increased pressure by the endotracheal tube after placement of deep retractors; deflation and re-inflation of the endotracheal tube during deep retractor placement decreased the risk of vocal cord paralysis from 6.4% to 1.69% (p = 0.0002). However, a recent randomized controlled trial did not demonstrate a difference when a similar protocol was employed.

One other controversial point is choosing a left- versus a right-sided approach. Previously it has been suggested that, due to a more unpredictable course of the right recurrent laryngeal nerve, a left-sided approach would result in fewer vocal cord-related complications. However, Kilburg et al found no statistical difference in recurrent laryngeal nerve palsy when comparing the side of approach. The side of approach is largely based on surgeon preference.

References

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Chang SW, Kakarla UK, Maughan PH, et al. Four-level anterior cervical discectomy and fusion with plate fixation: Radiographic and clinical results. Neurosurgery. 2010;66(4):639-46; discussion 646-7.
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