Neck pain is highly prevalent with approximately 15-20% of adults reporting at least one episode during any given year with degenerative disc disease (DDD) as a frequent cause. 1 Aging is the primary risk in developing DDD. As the United States (US) population ages, the incidence of cervical DDD has increased in kind. Though the initial treatment is typically conservative, the frequency of cervical spine surgeries in the US has increased substantially with a retrospective study finding the annual number of fusions for cervical spondylotic myelopathy increasing from 3,879 in 2003 to 8,181 in 2013. 2 The study also found that the average age of all fusion patients increased from 58.2 to 60.6 years (p<0.01). 2 Disc herniation, osteophytes, or an instability that compresses the cervical spinal cord can result in myelopathy, manifested by paresthesia, pain, or weakness of the arms or hands.
Anterior cervical discectomy and fusion (ACDF) has historically been considered the definitive surgical treatment for symptomatic DDD of the cervical spine. The goals of ACDF are to relieve pressure on the spinal nerves (decompression) and to restore spinal column alignment and stability. Cervical disc replacement (CDR) is a new surgical strategy that has recently emerged as a possible alternative to anterior cervical discectomy and fusion (ACDF), the more commonly used decompressive procedure in the cervical spine. In CDR, an artificial disc is secured in the prepared intervertebral space rather than an interbody cage and/or bone. Since an anterior plate is not required to stabilize the adjacent vertebrae and postsurgical orthosis is not usually required, it is hypothesized that CDR’s advantage is its ability to maintain anatomical disc space height, normal segmental lordosis, and physiological motion patterns at the index and adjacent cervical level with reduced risk of adjacent-level DDD commonly seen above or below a fusion site.3
CDR is equivalent to ACDF for surgical treatment of cervical DDD in select patient groups with the advantage of preserving motion.
Mummaneni et al (2007) reported the results of a prospective, randomized, multi-center study in which the results of CDR with the Prestige ST Cervical Disc System (Medtronic Sofamor Danek) were compared with anterior cervical discectomy and fusion (ACDF).4 Patients with symptomatic single-level cervical DDD who failed at least 6 weeks of conservative treatment or had signs of progression or spinal cord/nerve root compression with continued non-operative care were included in the study. Degenerative disc disease was determined to be present if a herniated disc and/or osteophyte formation were confirmed by history and radiographic studies (e.g., CT, MRI, x-rays). A total of 541 patients were enrolled at 32 sites and randomly assigned to 1 of 2 treatment groups: (i) 276 patients in the investigational group underwent anterior cervical discectomy and decompression and replacement with the Prestige ST Cervical Disc System; and (ii) 265 patients in the control group underwent decompressive ACDF. A total of 80% of the arthroplasty-treated patients (223 of 276) and 75% of the control patients (198 of 265) completed clinical and radiographic follow-up examinations at routine intervals for 2 years after surgery.4 Analysis of available post-operative 12- and 24-month data indicated a 2-point greater improvement in the neck disability index score in the investigational group than the control group.4 The arthroplasty group also had a statistically significant higher rate of neurological success (p = 0.005) as well as a lower rate of secondary revision surgeries (p = 0.0277) and supplemental fixation (p = 0.0031).4 The mean improvement in the 36-Item Short Form Health Survey Physical Component Summary scores was greater in the investigational group at 12 and 24 months, as was relief of neck pain. The patients in the investigational group returned to work 16 days sooner than those in the control group, and the rate of adjacent-segment re-operation was significantly lower in the investigational group as well (p = 0.0492, log-rank test).4The cervical disc implant maintained segmental sagittal angular motion averaging more than 7 degrees. In the investigational group, there were no cases of implant failure or migration. The authors concluded that the Prestige Cervical Disc maintained physiological segmental motion at 24 months after implantation and was associated with improved neurological success, improved clinical outcomes, and a reduced rate of secondary surgeries compared with ACDF.4 The FDA approved the Prestige Cervical Disc (Medtronic Sofamor Danek, Memphis, TN) for the treatment of single level cervical degenerative disc disease (C3 to C7) in 2007.
Sasso et al (2007) evaluated the functional outcome and radiographic results of the Bryan® artificial cervical disc replacement for patients with 1-level cervical disc disease.5 Twelve-month follow-up was available for 110 patients and 24-month follow-up was completed for 99 patients. There were 30 males and 26 females in the investigational group and 32 males and 27 females in the fusion group. The average age was 43 years (investigational) and 46 years (fusion). Disability and pain were assessed using the Neck Disability Index (NDI) and the VAS (Visual Analog Scale) of the neck and of the arm pain. SF-36 outcome measures were obtained including the physical component as well as the mental component scores. Range of motion was determined by independent radiologic assessment of flexion-extension radiographs. The average operative time for the control group was 1.1 hours and the investigational Group 1.7 hours. Average blood loss was 49 ml (control) and 64 ml (investigational). Average hospital stay was 0.6 days (control) and 0.9 days (investigational). The mean NDI before surgery was not statistically different between groups: 47 (investigational) and 49 (control). Twelve-month follow-up NDI is 10 (investigational) and 18 (control) (p = 0.013).5 At 2-year follow-up, NDI for the investigational group is 11 and the control group is 20 (p = 0.005).5 The mean arm pain VAS before surgery was 70 (investigational) and 71 (control). At 1-year follow-up, investigational arm pain VAS was 12 and control 23 (p = 0.031). At 2-year follow-up, the average arm pain VAS for the investigational group was 14 and control 28 (p = 0.014). The mean neck pain VAS before surgery was 72 (investigational) and 73 (control); 1-year follow-up scores were 17 (investigational) and 28 (control) (p = 0.05); 2-year follow-up: 16 (investigational) and 32 (control) (p = 0.005). SF-36 scores: Physical component before surgery investigational 34 and control 32; at 24 months: investigational 51 and control 46 (p = 0.009). More motion was retained after surgery in the disc replacement group than the plated group at the index level (p < 0.006 at 3, 6, 12, and 24 months).5 The disc replacement group retained an average of 7.9 degrees of flexion-extension at 24 months. In contrast, the average range of motion in the fusion group was 0.6 degrees at 24 months. There were 6 additional operations in this series: 4 in the control group and 2 in the investigational group. There were no intra-operative complications, no vascular or neurological complications, no spontaneous fusions, and no device failures or explanations in the investigational cohort. The authors concluded that the Bryan® artificial disc replacement compared favorably to anterior cervical discectomy and fusion for the treatment of patients with 1-level cervical disc disease. At the 2-year follow-up, there are statistically significant differences between the groups with improvements in the NDI, the neck pain and arm pain VAS scores, and the SF-36 physical component score in the investigational disc population.5
In 2007, the FDA approved the ProDisc™-C Total Disc Replacement (Synthes Spine, Inc.) for use in skeletally mature patients for reconstruction of the disc from C3-C7 following removal of the disc at one level for intractable symptomatic cervical disc disease (SCDD). The FDA's approval was based upon the results of a clinical trial (non-inferiority) involving 209 patients at 13 clinical sites comparing ProDisc™-C to ACDF.6 Patients with SCDD who failed at least 6 weeks of non-operative treatment or had progressive symptoms or signs of nerve root/spinal cord compression in the face of conservative treatment qualified for the trial. Intractable SCDD was defined as neck or arm (radicular) pain, and/or a functional/neurological deficit with at least one of the following conditions confirmed by imaging (CT, MRI, or x-rays): (i) herniated nucleus pulposus, (ii) spondylosis (defined by the presence of osteophytes), or (iii) loss of disc height. Patients were evaluated for pain and disability, neurologic status and range of motion at the index level. Patients were followed for 2 years post-surgery. The study data indicated that the ProDisc™-C is non-inferior to ACDF. According to the FDA-approved labeling, the ProDisc™-C should not be implanted in patients with an active infection, allergy to any of the device materials, osteoporosis, marked cervical instability, severe spondylosis, clinically compromised vertebral bodies at the level to be treated, and SCDD at more than one level.6
In 2009, the FDA-approved the Bryan® Cervical Disc (Medtronic Sofamor Danek) for use in skeletally mature patients for reconstruction of the disc from C3-C7 following single-level discectomy for intractable radiculopathy and/or myelopathy. The FDA's approval of the Bryan® Cervical Disc was based upon the results of a clinical trial (non-inferiority) involving 463 patients at 30 clinical sites comparing the Bryan device to ACDF.7 Patients with intractable radiculopathy and/or myelopathy resulting in impaired function with at least one clinical neurological sign associated with the cervical level to be treated and who failed at least 6-weeks of conservative treatment qualified for the trial. Intractable radiculopathy and/or myelopathy were defined as any combination of the following conditions confirmed by imaging (computed tomography, myelography and computed tomography, and/or magnetic resonance imaging): (i) disc herniation with radiculopathy, (ii) spondylotic radiculopathy, (iii) disc herniation with myelopathy, or (iv) spondylotic myelopathy. Patients were evaluated for pain and disability, and neurological status. Patients were followed for 2 years post-surgery. The study data indicated that the investigational CDR is non-inferior to ACDF.7 According to the FDA-approved labeling, the Bryan® Cervical Disc should not be implanted in patients with an active infection, allergy to any of the device materials, osteoporosis, moderate to advanced spondylosis, marked cervical instability, significant cervical anatomical deformity or compromised vertebral bodies at the index level, significant kyphotic deformity or significant reversal of lordosis, or symptoms necessitating surgical treatment at more than one cervical level. Because the specific polyurethanes used in the device have not be exhaustively studied for use as sheaths or nuclei in a cervical disc prosthesis, the FDA recommended that the sponsor continue to evaluate explanted devices in a 10 year post-approval study.
The FDA approved the SECURE-C Artificial Cervical Disc in 2012 based on the results of a non-inferiority study, which is intended to be used in skeletally mature patients to replace a cervical disc (from C3 to C7) following removal of the disc for conditions that result from a diseased or bulging disc (intractable radiculopathy or myelopathy) at only 1 level.8 The IDE trial compared the clinical safety and effectiveness of the selectively constrained SECURE-C (Globus Medical) Cervical Artificial Disc to ACDF. The study results demonstrated statistical superiority of the randomized investigational CDR group compared with the randomized ACDF group at 24 months, with a posterior probability of 100% using the protocol-specified criteria and 98.1% using Food and Drug Administration-defined criteria. At 24 months postoperatively, the investigational CDR group demonstrated clinically significant improvement in pain and function in terms of neck disability index, visual analogue scale, and 36-Item Short Form Health Survey. At 24 months, the percentage of patients experiencing secondary surgical interventions at the index level was statistically lower for the investigational CDR group (2.5%) than the ACDF group (9.7%).8
Contraindications of the Secure-C Artificial Cervical Disc:
- Active systemic infection or an infection at the operating site
- Allergy to the metals in the device (cobalt, chromium, molybdenum, or titanium), or to the type of plastic used in the device (polyethylene)
- Facet joint arthropathy
- More than 1 cervical disc requiring treatment (since device has only been evaluated in patients with 1 cervical disc requiring treatment)
- Osteoporosis or osteopenia
- Severe spondylosis
- Unstable cervical spine
- Weakened bones at the affected level due to current or past trauma
Safety and efficacy of 2-level CDR
On August 23, 2013, the FDA approved the Mobi-C® Cervical Disc Prosthesis for 2-level cervical disease. However, pivotal clinical studies excluded patients with DJD at more than 1-level. Beaurain et al reported the intermediate results of an undergoing multi-center prospective study of TDR with Mobi-C® prosthesis.9 These researchers evaluated (i) the safety and effectiveness of the device in the treatment of DDD and (ii) the radiological status of adjacent levels and the occurrence of ossifications, at 2-year follow-up (FU). A total of 76 patients had performed their 2-year FU visit and had been analyzed clinically and radiologically. Clinical outcomes (NDI, VAS, SF-36) and ROM measurements were analyzed pre-operatively and at the different post-operative time-points. Complications and re-operations were also assessed. Occurrences of heterotopic ossifications (HOs) and of adjacent disc degeneration radiographic changes have been analyzed from 2-year FU X-rays. The mean NDI and VAS scores for arm and neck were reduced significantly at each post-operative time-point compared to pre-operative condition. Motion was preserved over the time at index levels (mean ROM = 9 degrees at 2 years) and 85.5 % of the segments were mobile at 2 years. Heterotopic ossifications were responsible for the fusion of 6/76 levels at 2 years. However, presence of HO did not alter the clinical outcomes.9 The occurrence rate of radiological signs of ALD was very low at 2 years (9.1 %). There had been no subsidence, no expulsion and no sub-luxation of the implant. The authors concluded that these intermediate results of TDR appeared to confirm the safety and effectiveness of the device.9
Huppert et al (2011) compared the safety and effectiveness of disc replacement with an unconstrained prosthesis in multi- versus single-level patients.10 A total of 231 patients with cervical DDD who were treated with cervical disc replacement and completed their 24 months FU were analyzed prospectively: 175 were treated at 1-level, and 56 at 2-level or more.10 Comparison between both groups was based on usual clinical and radiological outcomes (NDI, VAS, ROM, satisfaction). Safety assessments, including complication and subsequent surgeries, were also documented and compared. Mean NDI and VAS scores for neck and arm pain were improved in both groups similarly. Improvement of mobility at treated segments was also similar. Nevertheless, in the multi-level group, analgesic use was significantly higher; and occurrence of HOs was significantly lower than in the single-level group. Subject satisfaction was nearly equal, as 94.2 % of single-level group patients would undergo the surgery again versus 94.5 % in the multi-level group.10 The overall success rate did not differ significantly. Multi-level DDD is a challenging indication in the cervical spine. This study showed no major significant clinical difference between the 2 groups.10 The major drawbacks of this exploratory study were small sample size, lack of randomization, and the p values suggested a trend towards similar results in the outcomes of single-level versus multi-levels populations.
Davis et al (2013) compared the Mobi-C® cervical artificial disc to ACDF for treatment of cervical DDD at 2 contiguous levels of the cervical spine.11 The primary clinical outcome was a composite measure of study success at 24 months. The comparative control treatment was ACDF using allograft bone and an anterior plate. A total of 330 patients were enrolled, randomized, and received study surgery. All patients were diagnosed with intractable symptomatic cervical DDD at 2 contiguous levels of the cervical spine between C3 and C7. Patients were randomized in a 2:1 ratio (TDR patients to ACDF patients). A total of 225 patients received the investigational CDR device and 105 patients received ACDF. At 24 months only 3.0 % of patients were lost to FU.11 On average, patients in both groups showed significant improvements in NDI score, VAS neck pain score, and VAS arm pain score from pre-operative baseline to each time-point. However, the CDR patients experienced significantly greater improvement than ACDF patients in NDI score at all time-points and significantly greater improvement in VAS neck pain score at 6 weeks, and at 3, 6, and 12 months post-operatively. On average, patients in the CDR group also maintained pre-operative segmental ROM at both treated segments immediately postoperatively and throughout the study period of 24 months. The re-operation rate was significantly higher in the ACDF group at 11.4 % compared with 3.1 % for the CDR group.11 Furthermore, at 24 months CDR demonstrated statistical superiority over ACDF based on overall study success rates.11 The authors concluded that the results of this study represented the first available Level I clinical evidence in support of cervical arthroplasty at 2 contiguous levels of the cervical spine using the Mobi-C® cervical artificial disc. Moreover, they stated that additional rigorous research will further the understanding of the safety and effectiveness of multi-level cervical arthroplasty and arthrodesis procedures.11
Alvin and Mroz (2014) evaluated the available literature on CDR with the Mobi-C® prosthesis, with a focus on 2-level CDR.12 All clinical articles involving the investigational disc prosthesis for CDR through September 1, 2014 were identified on Medline. Any paper that presented Mobi-C® CDR clinical results was included. Study design, sample size, length of follow-up, use of statistical analysis, quality of life outcome scores, conflict of interest, and complications were recorded. A total of 15 studies were included but only 1 of which was a level Ib RCT. All studies included showed non-inferiority of 1-level CDR to 1-level ACDF. Only 1 study analyzed outcomes of 1-level versus 2-level CDR, and only 1study analyzed 2-level CDR versus 2-level ACDF. In comparison with other cervical disc prostheses, the Mobi-C® prosthesis is associated with higher rates of heterotopic ossification (HO). Studies with conflicts of interest reported lower rates of HO. Adjacent segment disease or degeneration along with other complications was not assessed in most studies. The authors concluded that 1-level Mobi-C® CDR is non-inferior, but not superior, to 1-level ACDF for patients with cervical degenerative disc disease.12 They stated that Mobi-C® CDR procedure is associated with high rates of HO. However, they noted that insufficient evidence exists, thereby mandating a need for unbiased, well-designed prospective studies with well-defined outcomes in the future.12
In a meta-analysis, Zhao et al (2015) estimated the effectiveness of multi-level cervical disc replacement over single-level CDR for the treatment of cervical spondylosis and disc diseases.13 To compare the studies of multi-level CDR versus single-level CDR in patients with cervical spondylosis that reported at least one of the following outcomes: functionality, neck pain, arm pain, quality of life, re-operation and incidence of heterotopic ossification, electronic databases (Medline, Embase, PubMed, Cochrane library, and Cochrane Central Register of Controlled Trials) were searched. No language restrictions were used; 2 authors independently assessed the methodological quality of included studies and extracted the relevant data. Out of 8 cohorts that were included in the study, 4 were prospective cohorts and the other 4 were retrospective. The results of the meta-analysis indicated that there was no significant difference in neck disability index scores, neck VAS, arm VAS, morbidity of re-operation, heterotopic ossification, and parameters of living quality when comparing multi-level CDR with single-level CDR at 1 and 2 years follow-up post-operatively (p > 0.05).13 The authors concluded that the findings of this meta-analysis revealed that the outcomes and functional recovery of patients performed with multi-level CDR were equivalent to those with single-level CDA, which suggested the multi-level CDR was as safe and effective as single-level invention for the treatment of cervical spondylosis.13
A prospective randomized, US FDA investigational device exemption pivotal trial of the Mobi-C® cervical artificial disc was conducted at 24 centers in the U.S.14 A total of 330 patients with degenerative disc disease were randomized and treated with cervical total disc replacement (225 patients) or the control treatment, anterior cervical discectomy and fusion (ACDF) (105 patients). Patients were followed-up at regular intervals for 4 years after surgery. At 48 months, both groups demonstrated improvement in clinical outcome measures and a comparable safety profile. Data were available for 202 CDR patients and 89 ACDF patients in calculation of the primary end-point. CDR patients had statistically significantly greater improvement than ACDF patients for the following outcome measures compared with baseline: Neck Disability Index scores, 12-Item Short Form Health Survey Physical Component Summary scores, patient satisfaction, and overall success. ACDF patients experienced higher subsequent surgery rates and displayed a higher rate of ALD as seen on radiographs. Overall, CDR patients maintained segmental range of motion through 48 months with no device failure. The authors concluded that 4-year results from this study continue to support CDR as a safe, effective, and statistically superior alternative to ACDF for the treatment of degenerative disc disease at 2 contiguous cervical levels.14
In a prospective, randomized, multi-center FDA-Investigation Device Exemption (IDE) study using CDR as surgical treatment of DDD at 1 or 2 contiguous levels of the cervical spine, Bae et al (2015) evaluated the safety and effectiveness of CDR at single or 2 contiguous levels through 48 months of follow-up.15 Patients were randomized in a 2:1 ratio (CDR: ACDF) at 24 sites. Ultimately, 164 patients received TDR at 1 level and 225 patients received CDR at 2 contiguous levels. An additional 24 patients (15 1-level, 9 2-level) were treated with CDR as training cases. Outcome measures included neck disability index, VAS neck and arm pain, Short Form 12-item Health Survey (SF-12) Mental Composite Score (MCS) and Physical Composite Score (PCS), ROM, major complication rates, and secondary surgery rates. Patients received follow-up examinations at regular intervals through 4 years after surgery. Pre-operative characteristics were statistically similar for the 1- and 2-level patient groups. Four-year follow-up rates were 83.1 % (1-level) and 89.0 % (2-level). There was no statistically significant difference between 1- and 2-level CDR groups for all clinical outcome measures. Both CDR groups experienced significant improvement at each follow-up when compared with pre-operative scores. One case of migration was reported in the 2-level CDR group. The authors concluded that a 4-year post hoc comparison of 1- and 2-level CDR patients concurrently enrolled in a 24-center, FDA-IDE clinical trial indicated no statistical differences between groups in clinical outcomes, overall complication rates, and subsequent surgery rates. 15
In a prospective, multi-center, randomized, un-blinded clinical trial, Jackson et al (2016) evaluated subsequent surgery rates up to 5 years in patients treated with CDR or ACDF at 1 or 2 contiguous levels between C3 and C7.16 Patients with symptomatic DDD were enrolled to receive 1- or 2-level treatment with either CDR as the investigational device or ACDF as the control treatment. There were 260 patients in the 1-level study (179 CDR and 81 ACDF patients) and 339 patients in the 2-level study (234 CDR and 105 ACDF patients). At 5 years, the occurrence of subsequent surgical intervention was significantly higher among ACDF patients for 1-level (CDR, 4.5 % [8/179]; ACDF, 17.3 % [14/81]; p = 0.0012) and 2-level (CDR, 7.3 % [17/234]; ACDF, 21.0 % [22/105], p = 0.0007) treatment. The CDR group demonstrated significantly fewer index- and adjacent-level subsequent surgeries in both the 1- and 2-level cohorts. The authors concluded that 5-year results showed treatment with CDR results in a significantly lower rate of subsequent surgical intervention than treatment with ACDF for both 1 and 2 levels of treatment. The main drawbacks of this study included: (i) the inability to blind surgeons and patients to treatment, which opened the results to the potential of confirmation bias. Although the control group in this study was limited to anterior plating with allograft, other fusion procedures and devices (e.g., standalone devices and the use of autograft) were viable treatment options, (ii) the comparative results between the control and investigational groups were limited to anterior plate and allograft and may not be consistent with those of other surgical alternatives for cervical fusion, and (iii) the control group consisted of patients receiving 3 different cervical plate systems, based on surgeon preference. This heterogeneity represented a study limitation because ACDF failures may not have been equally distributed across the 3 fusion systems implanted.16
Long-term safety and efficacy outcomes of CDR
Quan et al (2011) evaluated the long-term outcome of CDR.17 A total of 21 patients underwent 27 total disc arthroplasties using the Bryan® cervical disc after anterior cervical discectomy. Clinical and radiological data were obtained from the 8-year post-operative review. Nineteen of 21 patients were able to perform daily activities without limitation; 20 of 21 patients reported fair to excellent outcome according to Odom criteria and 21 of 27 (78 %) operated segments were mobile. Functional prostheses moved an average of 10.6°, which was similar to the range of movement of the adjacent non-operated segments of the cervical spine. Heterotopic ossification was evident in 13 of the 27 (48 %) operated segments and restricted movement of the prosthesis in 9 cases. Five of the 6 patients who received bi-level disc replacements developed heterotopic ossification. There was 1 case of posterior migration of the prosthesis, which did not have any clinical repercussion. No other case showed evidence of migration, subsidence, loosening, or wear. Radiological evidence of ALD was observed in 4 patients (19 %); however, each of these patients had pre-existing degenerative disc disease at these levels on pre-operative imaging. The authors concluded that at 8-year follow-up, the Bryan cervical disc arthroplasty maintains favorable clinical and radiological results, with preservation of movement and satisfactory clinical outcome in the majority of cases.17 However, the incidence of heterotopic ossification causing restricted range of movement of the prosthesis appears to increase with time, especially in bi-level procedures.17
Coric et al (2013) evaluated the long-term results of CDR and ACDF in the treatment of single-level cervical radiculopathy.18 The results of two separate prospective, randomized, FDA Investigational Device Exemption pivotal trials (Bryan® Disc and Kineflex™|C) from a single investigational site were combined to evaluate outcomes at long-term FU. The primary clinical outcome measures included the NDI, VAS, and neurological examination. Patients were randomized to receive CDR in 2 separate prospective, randomized studies using the Bryan® Disc or Kineflex™|C cervical artificial disc compared with ACDF using structural allograft and an anterior plate. Patients were evaluated pre-operatively; at 6 weeks; at 3, 6, and 12 months; and then yearly for a minimum of 48 months. Plain radiographs were obtained at each study visit. A total of 74 patients were enrolled and randomly assigned to either the CDR (n = 41) or ACDF (n = 33) group. A total of 63 patients (86 %) completed a minimum of 4 years FU. Average follow-up was 6 years (72 months) with a range from 48 to 108 months. In both the CDR and ACDF groups, mean NDI scores improved significantly by 6 weeks after surgery and remained significantly improved throughout the minimum 48-month follow-up (p< 0.001).18 Similarly, the median VAS pain scores improved significantly by 6 weeks and remained significantly improved throughout the minimum 48-month follow-up (p < 0.001).18 There were no significant differences between groups in mean NDI or median VAS scores. The ROM in the CDR group remained significantly greater than the pre-operative mean, whereas the ROM in the ACDF group was significantly reduced from the pre-operative mean. There was significantly greater ROM in the CDR group compared with the ACDF group. There were 3 reoperations (7.3 %) at index or adjacent levels in the CDR group; all were cervical lamino-foraminotomies. There were 2 adjacent-level re-operations in the CDR group (4.9 %). There was 1 re-operation (3.0 %) in the ACDF group at an index or adjacent level (a second ACDF at the adjacent level). There was no statistically significant difference in overall re-operation rate or adjacent-level re-operation rate between groups. The authors concluded that both CDR and ACDF groups showed excellent clinical outcomes that were maintained over long-term follow-up. Both groups showed low index-level and adjacent-level re-operation rates. Both CDR and ACDF appeared to be viable options for the treatment of single-level cervical radiculopathy.18
Ren et al (2014) evaluated the mid- to long-term clinical outcomes after CDR as compared with ACDF for the treatment of symptomatic cervical disc disease.19 A systematic review and a meta-analysis were performed for articles published up to March 2013. Randomized controlled trials (RCTs) that reported mid- to long-term outcomes (greater than or equal to 48 months) after CDR as compared with ACDF were included. Two authors independently extracted the articles and the predefined data. A total of 5 RCTs that reported 4 to 6 years of follow-up data were retrieved. Patients who underwent CDR had a lower mid- to long-term rate of re-operation and had greater mid- to long-term improvements in the Neck Disability Index, neck and arm pain scores, and Short Form 36 Health Survey physical component score than did those who underwent ACDF. Segmental motion was maintained in patients who underwent CDR. The mid- to long-term rates of adjacent segment disease and neurological success were not significantly different between the 2 groups. The authors concluded that CDR may result in better mid- to long-term functional recovery and a lower rate of subsequent surgical procedures than ACDF would. Moreover, they stated that a review of the literature showed that only an insufficient number of studies had investigated adjacent segment disease; therefore, it is mandatory that adequate future research should focus in this direction.19
In a 10 year follow-up prospective, randomized-controlled clinical trial published in 2018 by Lavelle et al, 128 (CDR) and 104 (ACDF) patients were available for evaluation. Overall success rate was significantly higher for CDR group (81.3% vs. 66.3%; p = 0.005). Mean angular motions at index level for BRYAN® disc and ACDF were 8.69° and 0.60° respectively. These results confirm long-term preservation of motion in CDR compared to ACDF.20
Moreover, artificial disc replacement was assessed by the Washington State Health Technology Clinical Committee March 17, 2017 who concluded that cervical disc replacements were at least equivalent for safety and effectiveness compared to alternatives for some conditions.