Long-term Evaluation of Cervical Disc Arthroplasty with the Mobi-C© Cervical Disc: A Randomized, Prospective, Multicenter Clinical Trial with Seven-Year Follow-up

Abstract

Background: Cervical total disc replacement (TDR) is an increasingly accepted procedure for the treatment of symptomatic cervical degenerative disc disease. Multiple Level I evidence clinical trials have established cervical TDR to be a safe and effective procedure in the short-term. The objective of this study is to provide a long-term assessment of TDR versus anterior discectomy and fusion for the treatment of one- and two-level disc disease.

Methods: This study was a continuation of a prospective, multicenter, randomized, US FDA IDE clinical trial comparing cervical TDR with the Mobi-C© Cervical Disc versus ACDF through 7 years follow-up. Inclusion criteria included a diagnosis of symptomatic cervical degenerative disc disease at one or two cervical levels. TDR patients were treated using a Mobi-C© artificial disc (Zimmer Biomet, Austin TX, USA). ACDF with allograft and anterior plate was used as a control treatment. Outcome measures were collected preoperatively and postoperatively at 6 weeks, at 3, 6, 12, 18 months, annually through 60 months, and at 84 months. Measured outcomes included Overall success, Neck Disability Index (NDI), VAS neck and arm pain, segmental range of motion (ROM), patient satisfaction, SF-12 MCS/PCS, major complications, and subsequent surgery rate. The primary endpoint was an FDA composite definition of success comprising clinical improvement and an absence of major complications and secondary surgery events.

Results: A total of 599 patients were enrolled and treated, with 164 treated with one-level TDR, 225 treated with two-level TDR, 81 treated with one-level ACDF, and 105 treated with two-level ACDF. At seven years, follow-up rates ranged from 73.5% to 84.4% (overall 80.2%).The overall success rates of two level TDR and ACDF patients were 60.8% and 34.2%, respectively (p<0.0001). The overall success rates of one level TDR and ACDF patients were 55.2% and 50%, respectively (p>0.05). Both the single and two level TDR and ACDF groups showed significant improvement from baseline NDI scores, VAS neck and arm pain scores, and SF-12 MCS/PCS scores (p<0.0001). In the single level cohort, there was an increased percentage of TDR patients who reported themselves as "very satisfied" (TDR 90.9% vs ACDF 77.8%; p= 0.028). There was a lower rate of adjacent level secondary surgery in the single level TDR patients (3.7%) versus the ACDF patients (13.6%; p = 0.007).In the two level TDR group, the NDI success rate was significantly greater in the TDR group (TDR: 79.0% vs. ACDF: 58.0%; p=0.001). There was significantly more improvement in NDI change score at 7 years in the TDR patients versus ACDF. The TDR group had a significantly higher rate of patients who were "very satisfied" with their treatment compared to the ACDF group (TDR: 85.9% vs. ACDF: 73.9%). The rate of subsequent surgery at the index level was significantly lower in the TDR group compared to the ACDF group (TDR: 4.4% vs. ACDF: 16.2%; p=0.001). The rate of adjacent level secondary surgery was significantly lower in the two level TDR (4.4%) patients compared to the ACDF (11.3%; p=0.03) patients. In both single and two level cohorts, the percentage of patients with worse NDI (2.5%-3.8% of two level surgeries and 1.2%-2.5% of single level surgeries) or worse neck pain (5%-6.8% of the two level surgeries and 1.3% - 3.8% of the single level surgeries) was strikingly low in both groups but trended lower in the TDR patients.

Conclusions: At seven years, the composite success analysis demonstrated clinical superiority of two level TDR over ACDF and non-inferiority of single level TDR versus ACDF. There were lower rates of secondary surgery and higher adjacent level disc survivorship in both groups. Both surgeries were remarkably effective in alleviating pain relative to baseline and the rate of patients with worse disability or neck pain was surprisingly low. Overall, greater than 95% of patients (from both groups) who underwent TDR and 88% of patients who underwent ACDF were "very satisfied" at seven years. The differences in clinical effectiveness of TDR versus ACDF becomes more apparent as treatment increases from one to two levels, indicating a significant benefit for TDR over ACDF for two-level procedures.

Ethical standards: The Mobi-C Clinical Trial (ClinicalTrials.gov registration number: NCT00389597) was conducted at 24 sites in the US and was approved by the Institutional Review Board, Research Ethics Committee, or local equivalent of each participating site.

Level of evidence: 1.

Keywords: acdf; cervical total disc replacement; degenerative disc disease; mobi-c.

Conflict of interest statement

The device manufacturer, Zimmer Biomet (formerly LDR Spine), sponsored the Mobi-C© Cervical Disc FDA IDE clinical trial. Zimmer Biomet contributed to the design and conduct of the study and provided assistance with analysis of data and manuscript review. The authors also report receiving writing or editorial assistance for this paper from Zimmer Biomet. Dr. Radcliff: unpaid consultant for 4 Web Medical; board or committee member for ACSR; paid consultant for Altus Spine; paid consultant, research support, and unpaid consultant for DePuy, a Johnson & Johnson Company; intellectual property (IP) royalties, paid consultant, and research support from Globus Medical; unpaid consultant for Zimmer Biomet; paid consultant and research support from Medtronic; other financial or material support from NEXXT Spine; other financial or material support from NuVasive; paid consultant for Orthofix, Inc.; IP royalties and paid consultant for Orthopedic Sciences, Inc.; research support from Pacira pharmaceuticals; research support from Paradigm Spine; and other financial or material support from Stryker. Dr. Davis: consultant for Zimmer Biomet and Titan Spine. Dr. Bae: patent holder for Zimmer Biomet; research support from Zimmer Biomet; paid consultant for Zimmer Biomet; receives royalties for products from NuVasive, Stryker, and Zimmer Biomet. Dr. Hisey: consultant for Zimmer Biomet, DePuy/ Synthes Spine, and SAB Innovasis; patent holder for Zimmer Biomet. Dr. Nunley: direct stock ownership in Amedica, Paradigm Spine, and Spineology; has received support of non–study-related clinical or research effort from the Cervical Spine Research Society, K2M, Axiomed, Medtronic, Nutech, NuVasive, Spinal Motion, and Vertiflex; is a patent holder for K2M and Zimmer Biomet (specifically for the ROI-A anterior lumbar interbody fusion cage); is a consultant for Nutech, Amedica, K2M, and Zimmer Biomet; and has received royalties, performed speaking and teaching arrangements, and served on the scientific advisory board of Osprey Biomedical and K2M. Dr. Hoffman: direct stock ownership in Zimmer Biomet and Nanovis. Dr. Jackson: consultant for Zimmer Biomet; has received clinical or research support for this study from Zimmer Biomet; receives royalties from Globus Medical; stock ownership in Medtronic and Johnson and Johnson. Dr. Albert: board or committee member for Scoliosis Reseach Society; stock or stock options from ASIP; IP royalties from Biomet; stock or stock options from Biometrix; stock or stock options from Breakaway Imaging; stock or stock options from Crosstree; IP royalties and paid consultant for DePuy, a Johnson & Johnson Company; stock or stock options from Gentis; stock or stock options from InViVo Therapeutics; stock or stock options from Invuity; publishing royalties, financial or material support from Jay Pee; editorial or governing board Journal of Bone and Joint Surgery(American); stock or stock options in Paradigm Spine; publishing royalties, financial or material support from Saunders/Mosby-Elsevier; editorial or governing board for Spine; editorial or governing board for Spine Deformity Journal; stock or stock options in Spinicity; publishing royalties, financial or material support from Thieme; other financial or material support from United Healthcare; and stock or stock options in Vertech. Dr. Coric: royalties, stock ownership, and consultant for Spine Wave; stock ownership in DiscGenics and Spinal Kinetics; and consultant for Medtronic, Globus Medical, Stryker, and United Healthcare; and speaking and/or teaching arrangements for Globus.

Figures

Fig. 1

The Mobi-C© Cervical Disc.

Fig. 2

Overall treatment success of two-level TDR and ACDF.

Fig. 3

Patient-reported outcomes for two-level TDR and ACDF Patients from preoperative to 7 years follow-up. P-values are from global test of the difference between TDR and ACDF patient scores, generalized across all time points. Top Left: Mean NDI scores. Top Right: Mean VAS Neck Pain scores. Middle Left: Mean VAS arm pain scores. Middle Right: Mean SF-12 MCS. Bottom Left: Mean SF-12 PCS.

Fig. 4

Range of motion in flexion/extension (F/E) and lateral bending (LB) for two level patients. Top: Range of motion at the superior level. Bottom: Range of motion at the inferior level.

Fig. 5

Kaplan-Meier survival function estimates for subsequent surgery in two-level patients. P-value based on log-rank test. Left: Subsequent surgery for index level indications. Right: Subsequent surgery at the adjacent level.

Fig. 6

Overall treatment success of one-level TDR and ACDF.

Fig. 7

Patient reported outcomes for one-level TDR and ACDF Patients from preoperative to 7 years follow-up. P-values are from a global test of the difference between TDR and ACDF patient scores, generalized across all time points. Top Left: Mean NDI scores. Top Right: Mean VAS Neck Pain Scores. Middle Left: Mean VAS Arm Pain Scores. Middle Right: Mean SF-12 PCS. Bottom Left: Mean SF-12 MCS.

Fig. 8

Range of motion in flexion/extension (F/E) and lateral bending (LB) for one level patients.

Fig. 9

Kaplan-Meier survival function estimates for subsequent surgery in one-level patients. P-value based on log-rank test. Left: Subsequent surgery for index level indications. Right: Subsequent surgery at the adjacent level.