Cervical disc arthroplasty (CDA) has the potential to reduce the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion.1–3 The BRYAN Cervical Disc (Medtronic, Minneapolis, MN) is one of several CDA devices that have undergone safety and effectiveness evaluation in the United States. It currently has one of the longest follow-up periods available for review. After in vitro and in vivo testing4–6 demonstrated feasibility and adequate durability, a European prospective clinical trial, which began in 2000, demonstrated acceptable results at 2- and 4-year follow-ups.7–9 In a subsequent prospective, randomized, controlled clinical trial in the United States, Heller et al1 reported that the investigational group patients receiving the artificial disc showed improvement in all clinical outcome measures at the 2-year follow-up. They had a statistically greater improvement in the primary outcome variables of neck disability index (NDI) score (≥ 15-point improvement), maintenance or improvement in their neurologic status, no serious adverse events related to the implant or implant/surgical procedure, and no subsequent surgery or intervention that was classified as “failure.” More recent and longer term, randomized, control trials of 1-level treatment of the Prestige Cervical Disc (Medtronic, Minneapolis, MN),10–12 ProDisc-C (Depuy-Synthes Spine, Raynham, MA),13,14 and Mobi-C Cervical Disc (Zimmer Biomet, Warsaw, IN),15,16 have all reported similar or better clinical outcomes in the disc arthroplasty group and have found significantly less revision surgeries in the arthroplasty group after 4 to 7 years of follow-up.
Our study has assessed the long-term effectiveness and safety of the BRYAN cervical disc with up to 10 years follow-up of the original United States multicenter IDE trial.
MATERIALS AND METHODS
Patients and Study Design
Eligible patients who were enrolled in the initial study were at least 21 years old with radiculopathy or myelopathy from single-level cervical disc disease that had failed at least 6 weeks of nonoperative management, with the exception of myelopathy that required urgent treatment. Exclusion criteria included marked spondylosis; marked reduction or absence of motion or collapse of the intervertebral disc space of greater than 50% of its normal height; facet joint arthrosis; segmental instability or cervical kyphosis; active infection; metabolic bone disease, such as osteoporosis; known allergy to titanium, polyurethane, or ethylene oxide residuals; concomitant conditions requiring steroid treatment; diabetes mellitus; extreme obesity; pregnancy; inflammatory spondyloarthropathies, such as ankylosing spondylitis or rheumatoid arthritis, and previous cervical spine surgery.
All investigational sites had Institutional Review Board approval and all patients provided informed consent to participate in the study. Patients were randomly assigned in a 1:1 ratio to receive either an artificial disc (BRYAN) or fusion with anterior cervical plating and a bone allograft (ACDF). The randomization schedule was centrally generated by the sponsor, stratified by site by using a fixed block size of 4. Blinding for investigators and patients was maintained through confirmation of eligibility and informed consent. The surgeries were performed at 30 investigational sites by 65 investigators and coinvestigator surgeons. The control group's fusion procedure was standardized by using a commercially available allograft and a single anterior cervical plating system (Medtronic, Minneapolis, MN). The treatments were similar with neither group requiring cointerventions. Patients in both treatment groups followed a routine postoperative course and the investigational group was allowed to resume nonstrenuous activities as they pleased. Investigational group patients were treated with a 2-week postoperative course of a nonsteroidal anti-inflammatory drug of their surgeon's choice. Because of this difference between treatment groups and issues related to patient care, further blinding was not practical or ethical. Any decision to provide either soft or hard cervical collars was left to the discretion of the surgeon for both patient cohorts. As previously reported in the study by Heller et al,1, 463 enrolled patients were randomly assigned to the study groups: 242 patients received the investigational device and 221 patients underwent ACDF. This original set of patients was evaluated preoperatively, surgery/discharge, 1.5, 3, 6, 12, 24, 48, 60, 84, and 120-months after surgery.
The number of expected patients returning for follow-up has decreased over time for various reasons, including cumulative deaths; lost to follow-up; cumulative withdrawals of subjects who either terminated participation in the study or did not consent to a longer-term follow-up. At 120 months, of the original patients enrolled in the study, 54% (130/242) arthroplasty patients and 48% (105/221) fusion subjects were evaluated. On the basis of the number of subjects that were expected for each follow-up interval, the follow-up rates for the investigational and control groups at 12, 24, 48, 60, 84, and 120 months were 98.7%, 98.3%, 86.7%, 98.0%, 79.0%, 100%, and 95.7%, 96%, 79%, 97.6%, 79.5%, 100%, respectively.
Pain and function were assessed using the NDI,17,18 the Short Form-36 (SF-36),19 and Visual Analog Scales (VAS) for neck and arm pain. In addition, standardized neurologic examinations, including motor, sensory, and reflexes were recorded. Neurologic success required maintenance or improvement of all three neurologic parameters (motor, sensory, and reflexes). Radiographs were obtained before surgery, before hospital discharge, and at 3, 6, 12, 24, 48, 60, 84, and 120 months after surgery. All images were stored centrally and read by independent radiologists. All adverse occurrences were recorded prospectively, categorized, evaluated for causality, and graded for severity using World Health Organization criteria.12 These adverse effects were further reviewed for accuracy of categorization, causality, and severity by an independent physician.
The primary endpoint for the study was a composite measure termed “overall success,” which comprised the primary effectiveness and safety measures. To be considered an overall success, patients had to achieve all of the following: a ≥ 15-point improvement in their NDI scores, maintenance or improvement in their neurologic status, no serious adverse events related to the implant or implant/surgical procedure, and no subsequent surgery or intervention that could be classified as “failure.”
Overall success was predefined in the protocol, based on the US Food and Drug Administration's (FDA) recommendation and guidance for Investigational Device Exemption clinical trials for spinal devices. Investigational patients were evaluated for angular range of motion using the Cobb technique on dynamic radiographs. For each measurement, the means from two reviewers were calculated and used for analysis.
For control patients, successful fusion was defined as less than or equal to 4° of angular motion on lateral flexion and extension radiographs, the presence of bridging trabecular bone between the vertebrae being fused, and the absence of any radiolucent zones spanning more than 50% of the allograft surface. Two independent radiologists assessed the radiographs. In the event of disagreement about fusion healing, a third independent reading was obtained.
This clinical trial was based on a noninferiority hypothesis meaning that the overall success rate of the investigational group was statistically noninferior to that of the control group. The sample size of 225 patients per treatment arm was calculated for the original IDE study. For the post-market study, a sample size of a minimum of 100 patients each for control and investigational groups was planned. If noninferiority was established, then superiority would also be examined. For adverse events, additional surgical procedures or interventions, and surgery and hospital information, the null hypothesis was that the event rates or the means of a continuous variable between two groups were the same.
The primary analysis consisted of all patients who received one of the study treatments. Statistical comparisons were based on the observed and recorded follow-up data. A small number of patients required an additional surgical procedure (removal, revision, or supplemental fixation), and their outcomes were recorded as a treatment failure for overall success, which was the primary study endpoint. For other outcome variables, the observation before the second surgery was used for all future evaluation periods.
To compare patients’ demographic and preoperative measures, an analysis of variance was used for continuous variables and Fisher exact test was used for categorical variables. For comparing postoperative mean scores or mean score improvements measured in continuous scales, such as NDI scores, an analysis of covariance was utilized with the preoperative score as the covariate. For assessing statistical significance of improvement in outcome measures within each treatment group, a paired t test was used. For comparing days to return to work and event rates in the two treatment groups, the log-rank test was utilized. For comparing success rates, z-test of the normal approximation to the binomial distributions was used with the standard error derived from the Farrington and Manning method.
As defined in the protocol, one-sided P values were reported for most clinical outcomes except for surgery and return to work data, adverse events, and additional surgical procedures, which were two-sided. A P value of 0.05 was customarily considered as significant.
At the 10-year follow-up, 130 patients in the CDA group and 105 patients in the ACDF group were expected with an actual number of 128 and 104, respectively, evaluated for overall success.
Baseline characteristics of the patients and preoperative clinical measures were similar in the two groups except for the mean SF-36 mental component summary scores (MCS), body mass index (BMI), and range of motion (ROM) (Table 1).
Rates of neurologic success were similar for both treatment groups at all follow-up intervals. At 120 months, neurologic success occurred in 116 of 126 (92.1%) investigational and 98 of 103 (95.1%) control patients (P = 0.826). Motor success occurred in 123 of 126 (97.6%) investigational and 103 of 103 (100.0%) control patients (P = 0.943). Sensory success occurred in 120 of 126 (95.2%) investigational and 99 of 103 (96.1%) control patients (P = 0.627). Reflex success occurred in 125 of 126 (99.2%) investigational and 102 of 103 (99.0%) control patients (P = 0.443).
Before surgery, approximately 65% of patients in both study arms were employed. There were no differences between the groups at 24 months with 76.8% of investigational patients and 73.6% of control patients working. At 120 months, 96 of 126 (76.2%) investigational subjects and 66 of 103 (64.1%) control subjects were working.
At 120 months, the overall success rate (Figure 1) for the investigational group (81.3%) was significantly higher than the control group (66.3%) (P = 0.005). Survival analysis demonstrates that the BRYAN disc group had numerically lower rates of second surgeries at adjacent levels (9.7% vs. 15.8%), although the difference was not statistically significant (P = 0.146).
Neck Disability Index (NDI) Scores
At 120 months, mean NDI scores (Figure 2) improved significantly in the CDA group versus ACDF group (Δ38.3 vs. Δ31.1; P = 0.010). NDI success rate was significantly higher in the investigational patients (in 114/126, 90.5%) than that of control patients (78/103, 75.7%) (P = 0.001).
Visual Analog Scale Scores
Mean VAS neck improved by 54.3 for CDA patients and 49.2 for ACDF patients (Figure 3) (P = 0.119). Mean VAS Arm improved by 58.1 and 51.6, respectively (P = 0.060) (Figure 4) at 120 months.
SF-36 Summary Scores
Short Form-36 Physical Component Summary scores were significantly higher for the investigational patients with a mean score of 48.2 and 45.1 for control patients (P = 0.018). This corresponds to a mean change from the preoperative values of 14.9 for investigational and 12.6 for control patients (P = 0.018) at 120 months.
No new device-related serious adverse events were reported after 4 years for ACDF. The cumulative rate of serious adverse events related to the study device was 4.1% for CDA patients and 4.9% for ACDF patients. In the ACDF group, there was one excessive neck/arm pain, six nonunions (all of which required surgical intervention), and three spinal events (two at cervical adjacent level, one at cervical target level). In the CDA group, there was one reported implant loosening, one malpositioned implant, one excessive neck/arm pain, and five spinal events (all at cervical target level with three of these ultimately involving device removal).
Radiological Outcomes Measures
The mean preoperative ROM was 6.5° for the investigational group and 8.3° for the control group. Mean angular motions at index level for BRYAN disc and ACDF at 120 months were 8.7° and 0.6°, respectively (Figure 5).
Over the past decade, the BRYAN disc has been compared with ACDF for single-level cervical disc disease as the subject of a multicenter, prospective, randomized investigational device exemption trial. Early postoperative outcomes demonstrated statistically significant better improvement in NDI, VAS arm pain, and neck pain at 12, 24, and 48 months in the CDA group compared with ACDF.20,21 In addition, the SF-36 physical component improvement and the overall success rate were statistically better in the CDA group at 48 months. At 120 months, statistically significant improvements continued in NDI (Figure 2) and overall success. While still favoring CDA at 120 months, the VAS neck and arm pain scores were not statistically different (Figures 3 and 4). This course suggests that the BRYAN disc provides a clinically sound alternative to ACDF with some modest convergence of outcome over a decade. Similar support for clinical superiority of cervical arthroplasty over fusion pervades the literature, although there remains some debate.22–26
Motion preservation is a primary intent of CDA and the BRYAN disc demonstrated consistent significant maintenance of ROM at 3, 6, 12, 24, 48, and 120-month time points (Figure 5).20,21 In addition, mean angular motion actually improved slightly from 8.1° at 12 months to 8.5° at 24 months to 8.7° at the 120-month follow-up. While autofusion has been reported and the ROM may vary by device, other large trials of CDA have also suggested that CDA provides biomechanical stability and durability.11 It is also possible the patients with decreased ROM were among those lost to ultimate follow-up.
However, the number of expected subjects to follow-up dropped over time. The study had this limitation, as only about 54% (130/242) of enrolled CDA patients and 48% (105/221) of enrolled ACDF patients were evaluated for arthroplasty and fusion groups, respectively. This noted dropout rate could have substantially affected the overall results of the study, as the outcomes of the patients lost to follow-up cannot be obtained. In part, this was contributed to by the FDA's request for longer follow-up in conflict with the initial plan for 2-year follow-up in the initial study design. The barriers to patient and site participation and effect on follow-up have been well-described in the 48-month follow-up study.21 The study also does not comprehensively explore factors that have been shown to affect clinical outcomes following spine surgery such as other medical comorbidities and social factors. In addition, although this report describes range-of-motion as an indicator of implant performance, the long-term study of new implant technologies would ideally include a more comprehensive study of the prosthesis.27 More specifically, no effort was made to study osteolysis,28 metal hypersensitivity,29 or wear debris30 following CDA.
Challenges generalizing current data to a broad population also persist. The highly selected nature of those eligible for large prospective CDA trials raises concern about the efficacy in other populations such as those with more spondylosis at the symptomatic and at adjacent levels. In this study population, patients specifically had no substantial pathology or degeneration at the adjacent levels to the treated levels. In addition, by study design, this is a noninferiority study. Interpretation of these results should be based on these factors. Elements such as interpretation of required safety data such as neurological status not worsening likely has a substantial ceiling phenomenon. In other words, these are patients with single-level pathology without much in terms of substantial neurological deficits. Further, although the first decade of experience with the BRYAN disc serves a solid contribution to the data on safety and efficacy, many more decades of follow-up will be necessary to validate the longer-term results of CDA.31
The current study suggests that CDA can preserve motion and sustain clinical benefits over a decade. Readers should temper these potentially positive findings by viewing the data in light of the noninferiority design of the study itself and the dropout rate in the follow-up at the 120-month follow-up time point. While there may be some convergence of clinical benefit over time, there is maintenance of advantage in preserved motion and rates of reoperation for CDA.27 Future studies will be valuable to differentiate advantages of different implants, as CDA continues to be more widely adopted. While the experience with the BRYAN disc likely serves as a positive bellwether, study of pooled data and registries will be necessary to expose the truly long-term reality of CDA. It must be remembered that the available data are limited in predicting the natural history of CDA over the many decades of anticipated life expectancy of our patients.Key PointsCervical disc arthroplasty has the potential to reduce the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion.The BRYAN cervical disc has been studied with over 10 years of data currently being reported.Angular motion was preserved and improved with BRYAN cervical disc arthroplasty over the 10 years.There was a trend toward fewer adjacent segment surgeries with the BRYAN disc.
1. Heller JG, Sasso RC, Papadopoulos SM, et al. Comparison of BRYAN cervical disc
arthroplasty with anterior cervical
decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine (Phila Pa 1976)
2. Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical
arthrodesis. J Bone Joint Surg Am
3. Matsunaga S, Kabayama S, Yamamoto T, et al. Strain on intervertebral discs after anterior cervical
decompression and fusion. Spine (Phila Pa 1976)
4. Anderson PA, Rouleau JP, Bryan VE, et al. Wear analysis of the Bryan Cervical Disc
prosthesis. Spine (Phila Pa 1976)
5. Anderson PA, Sasso RC, Rouleau JP, et al. The Bryan Cervical Disc
: wear properties and early clinical results. Spine J
2004; 4 (6 suppl):303S–309S.
6. Jensen Wk, Anderson PA, Nel L, et al. Bone ingrowth in retrieved Bryan Cervical Disc
prostheses. Spine (Phila Pa 1976)
7. Goffin J, VanLoon J, VanCalenbergh F. Cervical
arthroplasty with the Bryan disc: 4-year results. Spine J
2006; 6 (5 suppl):62S–63S.
8. Goffin J, Casey A, Kehr P, et al. Preliminary clinical experience with the Bryan Cervical Disc
2002; 51:840–845. discussion 845–847.
9. Goffin J, Van Calenbergh F, VanLoon J, et al. Intermediate follow-up after treatment of degenerative disc disease with the Bryan Cervical Disc
Prosthesis: single-level and bi-level. Spine (Phila Pa 1976)
10. Burkus JK, Haid RW, Traynelis VC, et al. Long-term clinical and radiographic outcomes of cervical
disc replacement with the Prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg Spine
11. Burkus JK, Traynelis VC, Haid RW Jr, et al. Clinical and radiographic analysis of an artificial cervical
disc: 7-year follow-up from the Prestige prospective randomized controlled clinical trial: clinical article. J Neurosurg Spine
12. Mummaneni PV, Burkus JK, Haid RW, et al. Clinical and radiographic analysis of cervical
disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine
13. Murrey D, Janssen M, Delamarter R, et al. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease
. Spine J
14. Zigler JE, Delamarter R, Merrey D, et al. ProDisc-C and anterior cervical
discectomy and fusion as surgical treatment for single-level cervical
symptomatic degenerative disc disease: five-year results of a Food and Drug Administration study. Spine (Phila Pa 1976)
15. Hisey MS, Bae HW, Davis R, et al. Multi-center, prospective, randomized, controlled investigational device exemption clinical trial comparing Mobi-C Cervical
Artificial Disc to anterior discectomy and fusion in the treatment of symptomatic degenerative disc disease in the cervical
spine. Int J Spine Surg
16. Palmer MK. WHO handbook for reporting results of cancer treatment. Br J Cancer
17. Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther
18. Westaway MD, Stratford PW, Binkley JM. The patient-specific functional scale: validation of its use in persons with neck dysfunction. J Orthop Sports Phys Ther
19. McHorney CA, Ware JE Jr, Lu JF, et al. The MOS 36-item Short-Form Health Survey (SF-36): III. Tests of data quality, scaling assumptions, and reliability across diverse patient groups. Med Care
20. Sasso RC, Smucker JD, Hacker RJ, et al. Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients. Spine (Phila Pa 1976)
2007; 32:2933–2940. discussion 2941–2942.
21. Sasso RC, Anderson PA, Riew KD, et al. Results of cervical
arthroplasty compared with anterior discectomy and fusion: four-year clinical outcomes in a prospective, randomized controlled trial. J Bone Joint Surg Am
22. Hu Y, Lv G, Ren S, et al. Mid- to long-term outcomes of cervical
disc arthroplasty versus anterior cervical
discectomy and fusion for treatment of symptomatic cervical disc disease
: a systematic review and meta-analysis of eight prospective randomized controlled trials. PLoS One
23. Ma Z, Ma X, Yang H, et al. Anterior cervical
discectomy and fusion versus cervical
arthroplasty for the management of cervical
spondylosis: a meta-analysis. Eur Spine J
24. Wu AM, Xu H, Mullinix KP, et al. Minimum 4-year outcomes of cervical
total disc arthroplasty versus fusion: a meta-analysis based on prospective randomized controlled trials. Medicine (Baltimore)
25. Xie L, Liu M, Ding F, et al. Cervical
disc arthroplasty (CDA) versus anterior cervical
discectomy and fusion (ACDF) in symptomatic cervical
degenerative disc diseases (CDDDs): an updated meta-analysis of prospective randomized controlled trials (RCTs). Springerplus
26. Zhao H, Cheng L, Hou Y, et al. Multi-level cervical
disc arthroplasty (CDA) versus single-level CDA for the treatment of cervical
disc diseases: a meta-analysis. Eur Spine J
27. Makanji HS, Nwosu K, Bono CM. Editorial on “Long-term clinical outcomes of cervical
disc arthroplasty: a prospective, randomized, controlled trial” by Sasso et al. J Spine Surg
28. Kim SH, Chung YS, Ropper AE, et al. Bone loss of the superior adjacent vertebral body immediately posterior to the anterior flange of Bryan cervical disc
. Eur Spine J
29. Cavanaugh DA, Nunley PD, Kerr EJ 3rd, et al. Delayed hyper-reactivity to metal ions after cervical
disc arthroplasty: a case report and literature review. Spine (Phila Pa 1976)
30. Gornet MF, Singh V, Schranck RW, et al. Serum metal concentrations in patients with titanium ceramic composite cervical
disc replacements. Spine (Phila Pa 1976)
31. Boselie TF, vanSantbrink H. Arthroplasty in cervical
degenerative disc disease: fulfilling its long-term promise? J Spine Surg
Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
adjacent level disc degeneration; anterior cervical decompression and fusion (ACDF); BRYAN cervical disc; cervical angular motion; cervical disc arthroplasty (CDA); cervical disc disease; cervical