Anterior Cervical Discectomy

Anterior cervical discectomy (ACD) was described in the mid-20^th 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.

(Left) MRI, Sagittal T2 sequence, demonstrating a central cervical disk herniation causing cervical myelopathy. (Center) MRI, Axial T2 sequence, demonstrating a normal cervical disk that does not cause compression of the spinal cord or the exiting nerve roots. (Right) MRI, T2 Sequence, Axial T2 sequence, demonstrating a central disk herniation causing compression and deformation of the spinal cord, causing symptoms of cervical myelopathy.

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MRI, Axial T2 sequence, demonstrating a right-sided cervical disk herniation causing cervical nerve root impingement and resulting radiculopathy.

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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.