Anterior Cervical Discectomy

Anterior cervical discectomy (ACD) was described in the mid-20th century as a treatment for lateral cervical disc syndrome.[1, 2] This procedure involved removing the symptomatic disc from an anterior approach without placement of a bone graft. Early studies demonstrated fusion rates that were similar to those of procedures using bone graft.[2, 3] Multiple larger studies have also shown the ACD procedure to be safe and effective.[4, 5]

With the advent of ACD, anterior cervical discectomy and fusion (ACDF) techniques were simultaneously and independently popularized by Cloward[6] and Smith and Robinson.[7] ACDF similarly involves removing the symptomatic cervical disc with an added step of placing bone graft to encourage bony fusion of the upper and lower vertebral body. This added step has been argued to further encourage cervical fusion to maximize stability and maintain disc space height to decrease the likelihood of foraminal stenosis.[8] However, placement of a bone graft also introduces potential complications of graft dislodgement and failure, as well as donor-site complications if autograft is used. Nonetheless, the ACDF technique has been found to have excellent long-term clinical outcomes.[9, 10]

The anterior cervical discectomy and fusion with instrumentation (ACDFI) technique involves the additional stabilization of the cervical spine with instrumentation. Early instrumentation involved wiring techniques. This was largely modified to cervical plate technology after their introduction and application in the 1980s.[11] Design has subsequently improved to now include constrained, nonconstrained, rotational, rigid, and dynamic plate subtypes[12] . Argued benefits of plate instrumentation include reduced graft dislodgements, increased fusion rates, and decreased foraminal stenosis. However, as with the introduction of bone graft, the additional placement of hardware introduces hardware-related complications.

Since their introductions, heated debates have compared ACD, ACDF, and ACDFI. Prospective randomized controlled trials have been performed that demonstrate similar clinical outcomes between the 3 groups, with a decreased rate of cervical fusion and increased incidence of kyphosis in the ACD group.[3, 13, 14, 15] Guidelines were also published in 2009.[16] Proponents and detractors for these different procedures can be found throughout the scientific and surgical community.

The purpose of this article is not to compare and contrast these different surgical techniques or plate technologies but to highlight the role of these 3 procedures for treatment of cervical spine disease.

Key considerations

As mentioned above, ACD, ACDF, and ACDFI are different but very similar techniques for the surgical treatment of cervical spine disease. This article discusses the differences between these techniques.

When referring to the ACDFI technique, various plate technologies exist. These can be roughly categorized as rigid versus dynamic versus rotational, nonconstrained versus constrained, and rotational plating systems. Recent biodegradable and single-screw-per-vertebral body systems have also been introduced. The nuances of these plating systems are not discussed in this article.

When referring to the bone graft techniques, namely ACDF and ACDFI, surgical choices of using autograft and allograft exist. The differences between these types of bone graft are not discussed.

The indications for ACD, ACDF, and ACDFI include cervical spine trauma and resulting instability, radiculopathy, myelopathy, osteomyelitis, spondylosis, vertebral body tumors, opacified posterior longitudinal ligament, and postlaminectomy kyphosis.

Patient selection is important in complication prevention. Increased patient age, decreased bone density, and a positive smoking history can play a role in increasing complication rates. Additionally, an increase in the number of planned cervical levels to be decompressed can increase the complication risk.

Antibiotic infusions prior to skin incision should be used to decrease wound infection rates. Intraoperative fluoroscopic radiography should also be used to assess the cervical spine and facilitate proper hardware placement. An operative microscope that magnifies the operative field but also provides a strong light source is helpful. Intraoperative spinal cord monitoring has also been used as an effective measure for avoiding spinal cord and nerve root injury during surgical procedures.

Early studies demonstrated fusion rates that were similar to those of procedures using bone graft.[2, 3] Multiple larger studies have also shown the ACD procedure to be safe and effective.[4, 5]

The ACDF technique has been found to have excellent long-term clinical outcomes.[9, 10, 17]

Since their introductions, heated debates have compared ACD, ACDF, and ACDFI. Prospective randomized controlled trials have been performed that demonstrate similar clinical outcomes between the 3 groups, with a decreased rate of cervical fusion and increased incidence of kyphosis in the ACD group.[3, 13, 14, 15]

Complications specific to ACD, ACDF, and ACDFI include hardware and graft failures, neurologic injury, and neck-related complications.[18]

Hardware complications involve failures related to instrumentation. Reported incidence rates are from 1%-20%.[19, 20, 21] Hardware complications can include screw backout (2%-10%),[19, 20] plate fracture (2%),[20] screw breakage (1%-7%),[19, 20] , and plate migration (1%-3%).[22, 23] Graft fusion failures have also been described with an incidence that ranges from 3%-9%.[19, 20, 21, 22, 23] Interestingly, plate length, increasing age, use of allograft, and a reoperative procedure have been linked to a higher incidence of plate failure.[19, 24]

Neurologic complications can also occur with cervical procedures. These include dural tears leading to cerebrospinal fluid leaks, spinal cord injuries, and nerve root injuries resulting in weakness (1%-5%)[19] .[25]

Complications related to neck surgery are also possible. Dysphagia due to esophageal retraction and intubation has been reported to range from 4%-16%.[19, 20, 23] Postoperative neck hematoma causing airway obstruction has been reported.[19, 20] Esophageal perforations can also occur, especially during the opening approach to the vertebral body.

Garner-Wells tongs can be used for traction during the procedure but are not required. Self-retaining retractions are needed to maintain exposure of the operative field once the vertebral bodies are reached. An operative microscope is used to magnify the operative field and to provide a strong light source into the field. A rongeur and up-angled curette toolsets are needed to remove both herniated disc and bony osteophytes once the appropriate disc space is reached. If a fusion is to be performed, a high-speed drill can also be used to decorticate both the superior and inferior vertebral body endplates to encourage postoperative fusion.

If autograft is to be used, the appropriate surgical tools to harvest bone graft from the fibula or iliac crest are required. Fusion procedures require the addition of an instrument spacer to determine the size of the cage to be placed in the removed disc space. The addition of plate instrumentation also requires an appropriate drill tool for placement of screws.

Anesthesia

General anesthesia is used for all anterior cervical discectomy procedures. Local anesthetic is used just prior to skin incision.

Positioning

The patient should be positioned supine with the head extended. Gardner-Wells tongs can be used for both traction and head fixation. The arms can be pulled downward to increase operative exposure, especially for procedures involving the lower cervical spine.

Lateral radiographs are often used for long-term monitoring. These films allow the surgeon to assess for possible plate and graft complications. Alignment of the cervical spine, as well as adjacent level disease, can also be monitored with lateral radiographs. Occasionally, a CT scan or MRI of the cervical spine can be obtained to assess for procedure failure.

Patients are generally placed in a supine position with the head in an extended position. As noted above, Gardner-Wells tongs can be used for additional cervical traction. The hands can also be tied downward to increase the operative exposure. Once the surgical site is properly prepared with cleansing material, the appropriate surgical level is identified with intraoperative radiographs.

A scalpel is used to make a linear longitudinal incision just medial to the body of the sternocleidomastoid muscle. The incision is made long enough to include at least 2 vertebral levels if a 1-level discectomy is being performed. Alternatively, transverse skin incisions over the targeted vertebral level can also be performed. The platysmal muscle is identified and incised. The platysmal incision can be extended if a multilevel decompression is the surgical aim. Extensive subplatysmal dissection is performed to reduce retraction injury.

The esophagus is identified and retracted medially, while the sternocleidomastoid and underlying carotid sheath is retracted laterally. The prevertebral fascia is divided, and the longus colli musculature is further retracted. At this point, intraoperative radiographs should be obtained again to confirm the appropriate cervical level. Surgeons have recommended that electrocautery tools be avoided when operating below the C6 level to limit injury to the recurrent laryngeal nerve.

A self-retraction system can be used to maintain an open operative field. The retraction system should be released hourly to prevent ischemic injury. An operating microscope can also be used. The benefits of using an operative microscope include added magnification and focused lighting to improve visualization of the smaller and deeper surgical field. Moreover, the improved visualization may be advantageous in decompressing the nerve roots contralateral to the initial surgical approach.

Once properly visualized, the offending disc can be removed with a rongeur or drill set. As the posterior aspect of the vertebral body is reached, upward-curette tools can be used to maximize removal of osteophytes. The posterior longitudinal ligament should be visualized. Of note, if only an ACD procedure is being performed, the disc should not be entirely removed, and the cartilaginous endplates except for the posterior cortical margins should be left intact. If an ACDF or ACDFI is being performed, the entire disc should be removed and the vertebral body endplates must be decorticated with a drill. At this point, the ACD procedure is complete; the retractor system should be removed and closure of the surgical site can be initiated.

If an ACDF or ACDFI procedure is being performed, a bone graft must be placed in the open disc space. An applicator is often used to determine the graft size. The graft is then applied. If autograft is used, the fibula or iliac crest sites must be surgically prepared. The graft is then decorticated and processed for placement into the disc space. If plate instrumentation is to be used, the appropriate screw tools are used to properly screw the plates to the adjacent vertebral bodies. Lateral radiographs can be used to assess proper plate and screw placement intraoperatively.

At this point, the ACDF and ACDFI procedures are complete; the retractor system should be removed, and closure of the surgical site can be initiated. Postoperatively, a cervical collar can be worn for up to 6 weeks.