The anterior surgical options can be used for both single level and multilevel disease. The anterior approach is generally favored with soft disc herniations, concomitant severe axial neck pain, kyphosis, and with 1-2 levels of involvement ().
(a) Sagittal MRI demonstrating C5-6 extruded disc herniation. (b) Lateral radiograph of same patient after undergoing anterior cervical discectomy and fusion.
ACDF utilizes a Smith-Robinson approach to access the anterior surface of the cervical spine. After incision of the platysma, this approach involves little muscle disruption but opening of the pretracheal and prevertebral fascial planes to mobilize the midline structures of the neck. The decompression involves a thorough discectomy with removal of cartilaginous end plates and posterior osteophytes. A left-sided approach is preferred by some due to a more favorable course of the recurrent laryngeal nerve. Adequate decompression of the spinal cord may require removal of posterior osteophytes, partial corpectomy, or removal of the posterior longitudinal ligament (PLL); however all of these procedures increase the risk of injury to the spinal cord. ACCF is an alternative to multilevel ACDF and utilizes a similar approach, with either a transverse or longitudinal incision depending on number of levels. In this technique a central trough of vertebral body is progressively removed with a combination of a high-speed burr and rongeurs ().
Axial CT scan demonstrating fibula strut graft placed in central corpectomy trough.
The trough is centered between the uncovertebral joints, which helps orient the trough over the spinal cord and ensure complete decompression. Care must be taken to avoid eccentric bone removal laterally, endangering the vertebral arteries. A thin shell of the remaining posterior wall and posterior longitudinal ligament can then be removed with microcurrettes and Kerrisons. Fusion with ACDF and ACCF may be achieved with various graft options, including autologous tricortical iliac crest graft, allograft, polyetheretheketone (PEEK), or metal cages or a combination of morsellized bone from the corpectomy plus a structural allograft or cage. Plating is now common, especially with multilevel ACDF and ACCF [7
]. Complications with the anterior approach include vertebral artery injury (0.3%), esophageal injury (0.2–0.4%), wound infection (0.2–1.4%), and dysphagia (28–57%) [9
]. The cause of dysphagia appears to be multifactorial, including traction on the superior laryngeal nerve, pharyngeal plexus, recurrent laryngeal nerve, and esophageal retraction. Risk factors for dysphagia include age >60, multiple levels, revisions, females, thick plates, and longer preop pain [10
Advantages of ACDF or ACCF include ability to directly decompress offending structures, decompress the anterior spinal artery, restore cervical lordosis, and address axial neck pain. Multilevel ACDF is preferred in certain situations over ACCF where the compression is confined to the level of the disc spaces. Also, it is associated with a less blood loss and has a lower risk of graft kick out and catastrophic failure [11
]. However multilevel ACDF is associated with an increased risk of pseudarthrosis, as high as 54% in three-level fusions [12
]. Some surgeons use off-label recombinant human bone morphogenetic protein-2 (rhBMP-2) in these situations, but this should be undertaken with caution as there have been reports of airway compromise due to swelling [13
]. ACCF is preferred when compression extends behind the vertebral bodies to ensure that all areas of compression are addressed. When multilevel corpectomies are performed, there is potential for significant plate failure and graft extrusion, so supplemental posterior instrumentation should be considered [14
(a) Sagittal reconstructed CT scan of patient who underwent 3-level corpectomy. (b) Lateral radiograph of same patient. Posterior fusion was performed to increase stability of the construct.
Some have suggested that a potential benefit of ACCF is that fewer graft surfaces are required to fuse than multilevel ACDF (i.e., for a decompression at C4-5/C5-6, ACDF would require 4 surfaces to fuse versus 2 surfaces if treated with ACCF). Multiple studies have compared the fusion rates of ACCF and ACDF in an attempt to verify this benefit. Nirala et al. investigated 201 patients with multilevel noninstrumented anterior fusion and found that with more levels ACCF had a higher fusion rate than ACDF [15
]. Another study investigated 52 patients with multilevel anterior fusion with autograft and plate fixation and found similar clinical and fusion rates between ACCF and ACDF [16
]. With modern plating techniques, it appears that fusion rates are similar between the two techniques [17
]. A hybrid technique, combining selected corpectomies and discectomies, can be utilized where there is both retrodiscal and retrovertebral compression. Such a construct can increase stability and obviate the need for posterior supplementation. Shen et al. investigated the pseudarthrosis rate of multilevel anterior cervical fusion with rhBMP-2 and allograft using a hybrid technique in 127 patients [18
]. Overall pseudarthrosis rate was 10%, with 4% for three levels, 17% for four levels, and 22% for five levels. Nonunions typically occurred at the lowest level.
CDR is another anterior option in cases where cord compression is confined to the retrodiscal region. As a nonfusion option, this may provide the theoretical benefit of decreasing adjacent segment degeneration. Buchowski et al. compared ACDF with CDR for myelopathy at a single level disc space [19
]. These authors found similar improvement in neurologic status between the two groups at two years. Recently two-level CDR has come under investigation [20