Posterior Cervical Foraminotomy

Spurling and Scoville initially described posterior decompression for cervical radicular pain in the 1940s, before the introduction of anterior decompression. The technique consisted of a cervical laminectomy followed by removal of the disk. This approach evolved into the posterior cervical foraminotomy (PCF) described by Frykholm in the early 1950s, in which minimal bone is removed from the lamina and facet joint to decompress the exiting nerve root. The benefits of posterior decompression include direct visualization of the exiting nerve root and decompression without need for fusion and the resulting alteration of spinal kinematics. PCF is effective for posterolateral soft disk herniations as well as indirect decompression of neuroforaminal stenosis.

The patient’s head is stabilized in the prone position, and the level of decompression is determined by fluoroscopy. Subperiosteal dissection is performed down to the lamina, with the muscular attachments cephalad and caudad to the targeted level, and the interspinous ligament is left intact. A hemilaminotomy is performed, with the lateral portions of the lamina and medial aspect of the facet joint burred down with a high-speed burr under microscopic or loupe visualization. The cervical facet joint must be partially removed to expose and decompress the nerve root. Once the nerve root is identified, any remaining compressive bony or ligamentous lesion is carefully removed. If additional room is required to remove a soft disk herniation, a portion of the pedicle can be resected. The surgeon must be careful with the amount of facet joint removed, because removal of more than 50% of the facet results in significantly increased posterior strain and spinal instability and, therefore, should be avoided.

Anterior Cervical Diskectomy and Fusion

Smith and Robinson as well as Cloward described the anterior cervical diskectomy and fusion (ACDF) in 1958, and at present, it is the most widely used surgical procedure for cervical radiculopathy. The benefit of the anterior approach is the removal of ventral compressive lesions without the need for retraction of the spinal cord. Smith and Robinson advocated the removal of the disk and placement of an iliac crest bone autograft to encourage fusion. Osteophytes were not removed, because they were thought to resorb once a fusion was obtained and motion ceased. Cloward described the procedure with the use of cylindrical bone dowels filled with morselized autograft.

ACDF is performed supine with a bump between the shoulder blades to place the neck in gentle extension. The incision is marked with fluoroscopy and landmarks. Dissection is carried down through the skin and subcutaneous tissue to the platysma fascia. The fascia is split longitudinally to expose the medial border of the sternocleidomastoid muscle. The carotid sheath is palpated laterally, and the anterior cervical spine is approached using blunt dissection through fascial planes. The precervical spinal fascia is divided, and the longus colli muscle is mobilized laterally after a lateral radiographic image verifies the correct level. The disk is first removed to decompress the spinal canal followed by any osteophytes. The neuroforamin and exiting nerve roots are probed with a micronerve hook to ensure adequate decompression.

After the neural elements are decompressed, attention is turned to preparing the spine for fusion and placing the interbody graft. Although fusion without an interbody is described in the literature, there has been a decrease in the amount of anterior diskectomies done without fusion, secondary to an increased incidence of neck pain and postoperative kyphosis. An interbody graft assists with the expansion of the neuroforaminal space and it therefore provides indirect decompression of the nerve roots. There are multiple choices of interbody grafts, including autograft, allograft, and polyether ether ketone, that can be used. As the allograft has become more available, it has reduced the use of autograft bone because it does not have associated donor-site morbidity.

In the 1990s, cervical plates were introduced to augment stability. The addition of a cervical plate may help decrease the risk of pseudoarthrosis, maintain lordosis, and decrease the need for postoperative bracing because of the greater stability offered. However, the plates have been associated with an increased risk of dysphagia and implant failure due to screw loosening and backing out. Current plates are engineered to prevent screw back out, and thus this complication has been reduced. When using autograft, plating does not change the fusion rate when a 1 level fusion is performed, although the plate may prevent segmental kyphosis and graft subsidence. Plating does help increase the fusion rate when multiple levels are addressed, regardless of graft choice.

Cervical Disk Arthroplasty

The risk of adjacent segment degeneration both above and below a fusion led to the development of technologies to preserve cervical motion. The theoretical benefit of cervical disk arthroplasty (CDA) is the maintenance of motion at the diseased level. Motion within normal physiologic ranges theoretically helps to decrease stress at adjacent segments as compared with fusion, which has been shown to increase adjacent disk stress.

Numerous manufacturers have produced or are in the process of producing CDA devices. The Bryan cervical disc (Medtronic Sofamor Danek, Memphis, TN, USA) and the ProDisc-C (Synthes Spine Company, LP, West Chester, PA, USA) are 2 devices that have been through investigational device exemption (IDE) trials by the US Food and Drug Administration agency (FDA) to determine if equivalent performance exists with CDA compared with the ACDF, the current standard of care.

The surgical approach to the anterior cervical spine is the same as that for ACDF. Once the disk is removed and the neurologic structures are decompressed, the cartilaginous end plates are removed, leaving the bony end plates of the vertebral bodies to provide a firm foundation for the implant. A wider decompression is necessary because motion is preserved so that osteophytes may reform. A distracter is used to recreate the normal disk height, and trial devices are inserted to properly size the implant. The vertebral bodies are prepared as directed by the individual characteristics of the implant and then the implant is inserted and final implant positioning is confirmed with imaging. Patients undergoing CDA may receive antiinflammatory medication to decrease postoperative pain as well as potentially decrease the risk of heterotypic bone ossification. Because CDA hopes to maintain motion at the segment, the risk of pseudoarthrosis is eliminated, and this technique may help to decrease the risk of adjacent segment degeneration.

Anterior Cervical Foraminotomy

More recently, an anterior cervical foraminotomy (ACF) has been described to directly decompress the nerve root without fusion. Through this approach, a posterolateral disk herniation or foraminal stenosis can be addressed. Patient history, examination, and advanced imaging should all point to a well-defined anatomic site of unilateral nerve impingement. Patients should have predominant arm pain, because neck pain is a poor surgical indication. The approach is similar to that described for an ACDF, except the longus colli muscle is incised and kept lateral to expose the lateral disk and uncovertebral joint. Synder and Bernhardt first described a limited anterior foraminotomy, in which the lateral third of the disk was removed and the uncovertebral joint resected to decompress the nerve root. To improve outcomes and maintain the disk’s integrity, Jho altered the technique to leave as much of the disk intact, while removing the entire uncovertebral joint to decompress the nerve root. In this technique, the vertebral artery was exposed, which carried a risk of iatrogenic injury. Saringer and colleagues modified Jho’s technique by leaving the lateral wall of the uncovertebral joint intact during burring to protect the vertebral artery. Through this approach, they were still able to decompress the nerve root from its origin at the spinal cord to the point where it passes posterior to the vertebral artery. More recently, Lee and colleagues modified the technique by burring from the base of the uncinate process, leaving the intervertebral space intact. The uncinate process is not completely resected, and the investigators assert that the functional anatomy remains intact with no evidence of delayed instability in clinical follow-up.

Posterior Cervical Foraminotomy

Spurling and Scoville initially described posterior decompression for cervical radicular pain in the 1940s, before the introduction of anterior decompression. The technique consisted of a cervical laminectomy followed by removal of the disk. This approach evolved into the posterior cervical foraminotomy (PCF) described by Frykholm in the early 1950s, in which minimal bone is removed from the lamina and facet joint to decompress the exiting nerve root. The benefits of posterior decompression include direct visualization of the exiting nerve root and decompression without need for fusion and the resulting alteration of spinal kinematics. PCF is effective for posterolateral soft disk herniations as well as indirect decompression of neuroforaminal stenosis.

The patient’s head is stabilized in the prone position, and the level of decompression is determined by fluoroscopy. Subperiosteal dissection is performed down to the lamina, with the muscular attachments cephalad and caudad to the targeted level, and the interspinous ligament is left intact. A hemilaminotomy is performed, with the lateral portions of the lamina and medial aspect of the facet joint burred down with a high-speed burr under microscopic or loupe visualization. The cervical facet joint must be partially removed to expose and decompress the nerve root. Once the nerve root is identified, any remaining compressive bony or ligamentous lesion is carefully removed. If additional room is required to remove a soft disk herniation, a portion of the pedicle can be resected. The surgeon must be careful with the amount of facet joint removed, because removal of more than 50% of the facet results in significantly increased posterior strain and spinal instability and, therefore, should be avoided.

Anterior Cervical Diskectomy and Fusion

Smith and Robinson as well as Cloward described the anterior cervical diskectomy and fusion (ACDF) in 1958, and at present, it is the most widely used surgical procedure for cervical radiculopathy. The benefit of the anterior approach is the removal of ventral compressive lesions without the need for retraction of the spinal cord. Smith and Robinson advocated the removal of the disk and placement of an iliac crest bone autograft to encourage fusion. Osteophytes were not removed, because they were thought to resorb once a fusion was obtained and motion ceased. Cloward described the procedure with the use of cylindrical bone dowels filled with morselized autograft.

ACDF is performed supine with a bump between the shoulder blades to place the neck in gentle extension. The incision is marked with fluoroscopy and landmarks. Dissection is carried down through the skin and subcutaneous tissue to the platysma fascia. The fascia is split longitudinally to expose the medial border of the sternocleidomastoid muscle. The carotid sheath is palpated laterally, and the anterior cervical spine is approached using blunt dissection through fascial planes. The precervical spinal fascia is divided, and the longus colli muscle is mobilized laterally after a lateral radiographic image verifies the correct level. The disk is first removed to decompress the spinal canal followed by any osteophytes. The neuroforamin and exiting nerve roots are probed with a micronerve hook to ensure adequate decompression.

After the neural elements are decompressed, attention is turned to preparing the spine for fusion and placing the interbody graft. Although fusion without an interbody is described in the literature, there has been a decrease in the amount of anterior diskectomies done without fusion, secondary to an increased incidence of neck pain and postoperative kyphosis. An interbody graft assists with the expansion of the neuroforaminal space and it therefore provides indirect decompression of the nerve roots. There are multiple choices of interbody grafts, including autograft, allograft, and polyether ether ketone, that can be used. As the allograft has become more available, it has reduced the use of autograft bone because it does not have associated donor-site morbidity.

In the 1990s, cervical plates were introduced to augment stability. The addition of a cervical plate may help decrease the risk of pseudoarthrosis, maintain lordosis, and decrease the need for postoperative bracing because of the greater stability offered. However, the plates have been associated with an increased risk of dysphagia and implant failure due to screw loosening and backing out. Current plates are engineered to prevent screw back out, and thus this complication has been reduced. When using autograft, plating does not change the fusion rate when a 1 level fusion is performed, although the plate may prevent segmental kyphosis and graft subsidence. Plating does help increase the fusion rate when multiple levels are addressed, regardless of graft choice.

Cervical Disk Arthroplasty

The risk of adjacent segment degeneration both above and below a fusion led to the development of technologies to preserve cervical motion. The theoretical benefit of cervical disk arthroplasty (CDA) is the maintenance of motion at the diseased level. Motion within normal physiologic ranges theoretically helps to decrease stress at adjacent segments as compared with fusion, which has been shown to increase adjacent disk stress.

Numerous manufacturers have produced or are in the process of producing CDA devices. The Bryan cervical disc (Medtronic Sofamor Danek, Memphis, TN, USA) and the ProDisc-C (Synthes Spine Company, LP, West Chester, PA, USA) are 2 devices that have been through investigational device exemption (IDE) trials by the US Food and Drug Administration agency (FDA) to determine if equivalent performance exists with CDA compared with the ACDF, the current standard of care.

The surgical approach to the anterior cervical spine is the same as that for ACDF. Once the disk is removed and the neurologic structures are decompressed, the cartilaginous end plates are removed, leaving the bony end plates of the vertebral bodies to provide a firm foundation for the implant. A wider decompression is necessary because motion is preserved so that osteophytes may reform. A distracter is used to recreate the normal disk height, and trial devices are inserted to properly size the implant. The vertebral bodies are prepared as directed by the individual characteristics of the implant and then the implant is inserted and final implant positioning is confirmed with imaging. Patients undergoing CDA may receive antiinflammatory medication to decrease postoperative pain as well as potentially decrease the risk of heterotypic bone ossification. Because CDA hopes to maintain motion at the segment, the risk of pseudoarthrosis is eliminated, and this technique may help to decrease the risk of adjacent segment degeneration.

Anterior Cervical Foraminotomy

More recently, an anterior cervical foraminotomy (ACF) has been described to directly decompress the nerve root without fusion. Through this approach, a posterolateral disk herniation or foraminal stenosis can be addressed. Patient history, examination, and advanced imaging should all point to a well-defined anatomic site of unilateral nerve impingement. Patients should have predominant arm pain, because neck pain is a poor surgical indication. The approach is similar to that described for an ACDF, except the longus colli muscle is incised and kept lateral to expose the lateral disk and uncovertebral joint. Synder and Bernhardt first described a limited anterior foraminotomy, in which the lateral third of the disk was removed and the uncovertebral joint resected to decompress the nerve root. To improve outcomes and maintain the disk’s integrity, Jho altered the technique to leave as much of the disk intact, while removing the entire uncovertebral joint to decompress the nerve root. In this technique, the vertebral artery was exposed, which carried a risk of iatrogenic injury. Saringer and colleagues modified Jho’s technique by leaving the lateral wall of the uncovertebral joint intact during burring to protect the vertebral artery. Through this approach, they were still able to decompress the nerve root from its origin at the spinal cord to the point where it passes posterior to the vertebral artery. More recently, Lee and colleagues modified the technique by burring from the base of the uncinate process, leaving the intervertebral space intact. The uncinate process is not completely resected, and the investigators assert that the functional anatomy remains intact with no evidence of delayed instability in clinical follow-up.

PCF Outcomes

PCF has demonstrated excellent results when performed for the correct indications while maintaining motion at the diseased vertebral segment. In a retrospective study, Henderson and colleagues reported good to excellent results in 91.5% of 846 patients, with resolution of radicular symptoms and motor deficits in 96% and 98%, respectively. Complications such as wound infection and dehiscence were observed in 1.5%, while a radiculopathy recurrence rate of 3.5% was demonstrated. They recommended PCF for simple cervical radicular problems. Tomaras and colleagues observed similar results in a review of 182 patients who underwent PCF and found that 93% of patients had a good to excellent result after a mean of 19 months.

Jagannathan and colleagues, in a recent retrospective review of 162 single-level PCFs performed for unilateral radiculopathy, concluded that the procedure was highly successful. About 93% of patients had an improvement in their neck disability index (NDI), and 95% had resolution of radicular symptoms. These outcomes were maintained at a mean follow-up of 77 months.

Tumialan and colleagues, in a retrospective review of military personnel with unilateral cervical radiculopathy, found that posterior foraminotomy offered a significant cost benefit compared with ACDF in both the short- and long-term. This advantage was secondary to patients not requiring instrumentation and interbody grafts. No significant difference was observed in the success of the procedures, defined as a return to active duty, but the patients who underwent PCF were able to return to active duty faster and at a lower cost.

Although PCF provides excellent results in the proper patient, risks exist. A radiographic review at a mean of 77 months by Jagannathan and colleagues demonstrated no significant changes in either focal or segmental kyphosis and no changes in disk space height. However, loss of lordosis (defined by Cobb angle <10°) was observed in 20% of patients and represented the most common complication in Jagannathan’s series. Although there was no significant risk for worsening of kyphosis in the general population, some patient subsets demonstrated loss of lordosis. Risk factors for worsening of sagittal alignment were age greater than 60 years at the time of the initial surgery, preoperative loss of lordosis, and need for further posterior surgery after the initial foraminotomy. The extent of decompression, violation of the posterior muscular and ligamentous tension band, and resection of the facet joints all play a role in the loss of cervical alignment.

Although ACDF is associated with adjacent segment degeneration, it also occurs with PCF. Clarke and colleagues reviewed 303 patients who underwent single-level PCF and found that the 10-year risk of adjacent segment degeneration was 6.7%. Jagannathan and colleagues, at 8-year follow-up, found adjacent segment degeneration in 4.9% of patients, with a risk of developing it being 1.2% per year. These rates are less than those found in ACDF, as observed in the study by Hilibrand and colleagues on adjacent segment degeneration after ACDF.

In addition to kyphosis and adjacent segment degeneration, postoperative instability was found in 4.9% of patients in the series by Jagannathan and colleagues, but only 1 of 8 patients was symptomatic requiring fusion. Other complications included cerebrospinal fluid leak in 2.5% and C5 nerve root injury in 1.2% of the patients. In other series, nerve root injuries have been described in as many as 10% of the patients.

Woertgen and colleagues, in a prospective consecutive study of 54 patients who underwent PCF, found that a long duration of symptoms and neurologic deficits were important prognostic factors for a poor outcome. Also, patients with neck pain do not respond as well to PCF. Overall, PCF is good procedure with excellent results when performed in the patient with the proper indications.

ACF Outcomes

Outcome data for ACF are limited to a small number of short-term follow-up studies reviewing multiple technique variations. Snyder and Bernhardt reviewed 63 patients at a mean follow-up of 23 months and found that 64% of the patients had a good to excellent outcome, whereas more than one-third of the patients had either a fair or poor outcome. The technique of Snyder and Bernhardt involved removing some of the disk and retaining some of the uncovertebral joint, which may have left residual compression and destabilized the joint. On an average, patients lost 1 mm of disk height, and 4% went on to experience spontaneous fusion. Despite this consequence, 85% of the patients were satisfied by their results. Hacker and Miller, in a retrospective review of 23 patients who underwent ACF, found that 52% had a good to excellent outcome, whereas 30% required an additional procedure. The investigators raised issue over the number of poor results and the increased reoperation rate compared with other cervical radiculopathy treatments. These rates may be due to the development of postoperative spinal instability at the operated level.

Although the 2 previous studies demonstrated negative results, several studies have demonstrated positive findings. Johnson and colleagues, using Jho’s technique of not violating the disk, retrospectively reviewed 21 patients treated with ACF. They found that 91% of the patients either had improved or resolved radicular symptoms. No evidence of spinal instability in flexion or extension was observed at the short-term follow-up of 3 months of the studies. Saringer and colleagues reviewed 34 patients with 2 to 17 months of follow-up and determined that 97% of patients had improvement in both neck pain and radicular symptoms. Paresis and numbness improved in most patients but took longer. Equal success was observed in both 1 and 2 level decompressions. Lee and colleagues reviewed 13 patients followed up for a mean of 19 months, with all patients getting 100% relief from radicular symptoms without evidence of instability. VAS score improved from 9.6 preoperatively to 2 postoperatively, with NDI score improvement from 41 to 16.

Similar to PCF’s problem with excessive facet joint resection, unilateral uncovertebral joint resection can affect the stability of the spinal motion segment. Chen and colleagues demonstrated that resection of the unilateral uncovertebral joint alters normal spinal motion. Kotani and colleagues sequentially resected different portions of the uncovertebral joint and found that the foraminal segment, resected with ACF, contributed the most to spinal segment stability. In addition, they demonstrated that uncovertebral joint resection resulted in a decreased overall stability of the spinal segment. No long-term studies exist as they do for ACDF evaluating the effect of ACF on the motion segment, disk degeneration, and adjacent segment degeneration.

Although the studies reviewing ACF have demonstrated mostly positive results, several questions exist. Hacker and Miller specifically raised issue with the results of ACF and did not recommend the procedure as a stand-alone treatment for cervical radiculopathy. Overall, the studies do not present long-term results and represent several different technique variations. Further long-term data are needed to shed light on the viability of ACF.

ACDF Outcomes

ACDF has been used for many decades with good results in treating cervical radiculopathy. White and colleagues demonstrated good to excellent results in 76% of patients who underwent ACDF for radicular symptoms. They found that a successful fusion led to better results. Bohlman and colleagues reviewed the outcomes of 122 patients who underwent 1 to 4 level ACDF with autogenous iliac crest bone graft, with an average follow-up of 6 years. They demonstrated that 93% of patients had no pain or only mild pain and were considered good to excellent outcomes. Of the 122 patients, 55 had neurologic deficits preoperatively and all but 2 had complete resolution of their symptoms. They determined that overall, ACDF was a safe procedure that can relieve pain and lead to a resolution of neurologic symptoms in a large percentage of patients.

Recently, good outcome data regarding ACDF have been published from the randomized controlled multicenter clinical trials evaluating CDA, in which ACDF was used as the control. Heller and colleagues demonstrated that ACDF caused a significant reduction in arm and neck pain from preoperative values. A 15-point reduction in the NDI was demonstrated with a 1 level ACDF, with maintenance or improvement of neurologic status in 90.2% of patients. In addition, significant improvement was observed in the 36-Item Short Form Health Survey (SF-36) scores, mental health scores, as well as in NDI scores. Improvements in SF-36 scores after ACDF were found to be greater than or equal to the improvement observed after total knee and hip arthroplasty. Radiographic evaluation identified a nonunion rate of roughly 6% in the 1 level ACDF with an allograft spacer and plate at 24 months. Results were maintained at 2-year follow-up. Overall, when looking at multiple variables with a 1 level ACDF, success was observed in 72.7% of patients.

The study by Murrey and colleagues on CDA also demonstrated good results after ACDF. About 78% of patients who underwent 1 level ACDF had a successful reduction of their neck disability (success was characterized by the FDA as a 15-point improvement in NDI) and improvement in SF-36 scores. Neurologic success rate, defined as maintenance or improvement of neurologic function, was observed at 2-year follow-up in 88% of patients who underwent ACDF. About 83% of patients who underwent ACDF were completely satisfied, with 80.9% stating that they would undergo the procedure again. Fusion rate was determined to be 90.2% at 24 months, and 8.5% of patients who underwent ACDF required a secondary surgical procedure within the follow-up period. There was a significant improvement at all time points for the ACDF population in SF-36 score improvement from baseline. Overall, success was observed in 68.3% of patients who underwent fusion, when all the FDA-defined criteria were composited.

Although ACDF has been performed for many years and has demonstrated good overall outcomes and low morbidity, risks exist. They include dysphagia (up to 60%), dysphonia (up to 51%), injury to the esophagus, pseudoarthrosis, and hardware failure. Morbidity can be affected by several different variables, such as smoking history, number of levels fused, plating, and type of graft used. There is an increased risk of dysphagia and dysphonia in patients who have preoperative complaints of these conditions before surgery. In addition, patients with gastroesophageal reflux disease also have an increased risk of postoperative complaints with breathing, voice, and swallowing and they should be counseled appropriately.

Bohlman and colleagues found that pseudoarthrosis risk increased with the number of levels treated and that there was a significant association between postoperative pain and pseudoarthrosis. Zdeblick and colleagues demonstrated that reoperation for symptomatic pseudoarthrosis or persistent symptoms after ACDF can lead to excellent outcomes, as shown by 83% of patients after revision.

An additional risk associated with ACDF is adjacent segment degeneration leading to a return or development of new symptoms. Adjacent segment degeneration has been reported to occur in 3% to 8% of patients per year as a consequence of ACDF. Hilibrand and colleagues determined that adjacent segment degeneration occurred at a relatively constant incidence of 2.9% per year for the first 10 years after cervical arthrodesis. In addition, survivorship analysis predicted that 25.6% of patients would have new degeneration within 10 years. This degeneration is believed to be secondary to genetics, the natural progression of cervical disease, and increased stress at adjacent levels after fusion due to altered spinal kinematics. Hilibrand and colleagues found that adjacent degeneration was less likely after a multilevel fusion when compared with a single-level fusion.

CDA Outcomes

Although the studies on CDA provide a good indication of ACDF success rate, they primarily provide information on the CDA and its comparison to ACDF. Heller and colleagues, in a prospective randomized clinical IDE trial, examined the results of the Bryan cervical disc and ACDF (control) at 2-year follow-up. The indication for surgery was radiculopathy or myelopathy in patients with single-level cervical pathologic condition. At 2-year follow-up, the radiographic range of motion was 8.1° ± 4.8° in the investigational group, demonstrating continued segment motion. The artificial disk group had a statistically superior improvement in NDI compared with ACDF group and an overall higher rate of overall success at 2 years. Overall success was measured with a composite score comprised of clinical and safety outcomes. Although arm pain reduction and SF-36 scores were similar in both groups, the arthroplasty group demonstrated a significantly greater improvement in neck pain at all time points. Patients who underwent arthroplasty returned to work 13 days earlier than those who underwent fusion, which was statistically significant. No difference was observed in adverse events between ACDF and CDA. Overall, cervical disk replacement was recommended as a viable alternative to ACDF.

Murrey and colleagues reported on the 2-year data from 209 patients in the FDA IDE study of the ProDisc-C. There were no differences observed between CDA and ACDF regarding neck and arm VAS scores, NDI, SF-36, or neurologic status at 24 months. Although there was a significantly increased operative time (8.5 minutes) and blood loss (20 mL) with arthroplasty, the arthroplasty group demonstrated a decreased reoperation rate (1.8% vs 8.5%) as compared with ACDF. The IDE study by Murrey and colleagues demonstrated that the CDA was safe and effective at 24 months compared with ACDF.

To date, the US multicenter CDA IDE studies have only released their 2-year cumulative results, with longer follow-up expected. However, Garrido and colleagues reviewed the 48-month data from a single institution involved in the prospective Bryan IDE trial and demonstrated no decrease in the outcomes for arm or neck VAS, NDI, or SF-36 compared with ACDF at 4 years. In addition, patients who underwent CDA continued to require less number of secondary surgeries.

Goffin and colleagues published longer-term observational results of CDA from a multicenter European study evaluating arthroplasty using Bryan cervical disc in 98 patients (89 [1 level] and 9 [2 level]) without a control group. CDA was performed for radiculopathy or myelopathy associated with spondylosis and/or disk herniations unresponsive to conservative treatment. The investigators found the favorable clinical outcomes noted at 2 years were maintained at the intermediate time points of 4 to 6 years. SF-36, NDI, and neck and arm pain results were all improved compared with preoperative values and maintained over the course of the study. Motion was maintained within 2° of the preoperative value in more than 83% of patients who underwent 1 level arthroplasty demonstrating motion greater than 2° (2° was the cut-off point for showing motion existed). Although motion existed, it was decreased at the 4- and 6-year follow-up as compared with the 1- and 2-year time points. Only 5.8% of patients experienced adverse events secondary to the arthroplasty device. Overall, the favorable clinical and angular motion outcomes that were noted at 1- and 2-year follow-up persist at 4- and 6-year follow-up. Time will determine if this finding holds true for the more rigorous US FDA studies.

CDA shares the same surgical approach with ACDF, and many of the surgical risks are similar. Anderson and colleagues reviewed the adverse events that occurred during the Bryan IDE study at 24 months. There were no significant differences in the overall medical events between CDA and ACDF. Although the CDA group had more surgically related adverse events than the ACDF group, they tended to be less severe, such as dysphagia or late medical events. Overall, although the ACDF group had fewer events, the events were more severe because of the treatment of pseudoarthrosis and persistent symptoms requiring a higher rate of reoperation. Both procedures were demonstrated to be safe, with overall low incidences of adverse events.

Walraevens and colleagues, in a prospective longitudinal study, found that mobility at the CDA-treated level was preserved in 85% or more of the 84 patients studied at 8-year follow-up. Although increased segmental motion was not observed at adjacent levels, disk degeneration increased at adjacent levels, a condition CDA attempts to mitigate. The increase in degeneration at adjacent levels was commensurate to disk degeneration observed in natural age-related studies and less than that found in ACDF studies. Radiographic evidence of heterotopic ossification was found in up to 39% of patients at the treated level within the first 4 years and remained stable beyond that. No patient exhibited anteroposterior device migration or subsidence. CDA maintains preoperative motion at the index and adjacent levels and seems to protect against acceleration of adjacent-level degeneration as is often observed later.

Recently, CDA is being used by combining it with fusion or above or below a previous fusion. Barbagallo and colleagues reported on using a hybrid of CDA and fusion for patients with multilevel disease in 2 level, 3 level, and 4 level surgeries. They found it to be safe and reliable, with good maintenance of results with follow-up of 12 to 40 months. In addition, Phillips and colleagues observed single-level CDA adjacent to prior ACDF compared with CDA in patients without previous fusion. They found that both groups demonstrated significant improvement in NDI and VAS after surgery, without significant difference between the 2 groups. Despite increased biomechanical forces at the level adjacent due to fusion, CDA did well in the short-term, although longer-term follow-up is required.

Comparison of Anterior and Posterior Procedures

The literature contains few studies that review both anterior decompression with ACDF and posterior decompression with PCF. Herkowitz and colleagues prospectively reviewed 33 patients who underwent treatment of posterolateral cervical soft disk herniations with either an anterior (ACDF) or posterior (PCF) approach. About 94% of patients who underwent ACDF had a good to excellent result, whereas 75% who underwent PCF had similar results. Onimus and colleagues reviewed anterior and posterior decompression for soft posterolateral cervical disk herniations, with similar results between the 2 groups.

In well-selected patients with unilateral radiculopathy, decompression of the lateral recess and neuroforamin by either ACDF or posterior foraminotomy has been found to be efficacious. Additional studies using current treatment options, including CDA and minimally invasive PCF, would be beneficial in determining the ideal approach. Trends in the United States over the past few decades have shifted in favor of an anterior approach. However, it has been recently suggested that PCF may play a larger role in the future with the introduction of newer minimally invasive techniques and the decreased cost and risks due to not needing instrumentation and fusion.