7-year Outcomes for Single-Level Total Disc Replacement with a Novel Viscoelastic Artificial Cervical Disc

Introduction: The M6-C Artificial Cervical Disc, with a compressible viscoelastic nuclear core and an annular structure, is substantially different from first-generation articulating surface designs.

Methods: A prospective, multicenter, controlled IDE clinical trial is currently in long-term follow-up. 12 M6-C sites are participating in the study, with pre-operative assessments followed by 6 weeks, 3 months, 6 months, 1 year, and annually out to 10 years post-implantation. 160 M6-C subjects were enrolled. Study subjects presented with one-level symptomatic degenerative cervical radiculopathy.

Results: NDI and Pain Scores are available for 93 M6-C subjects at 7 years post-op. M6-C subjects had a mean Neck Disability Index (NDI) score of 9.3 on a 100-point scale, indicating mild disability. M6-C subjects experienced a mean NDI improvement from baseline of 46.5 points at 7 years. Similarly, M6-C subjects had a mean Neck Pain VAS Score of 0.8 (out of 10) and a mean Shoulder/Arm Pain VAS Score (worst side) of 0.5.

Through 7 years post-op, 11 of the 160 enrolled M6-C subjects (6.9%) experienced Subsequent Surgical Interventions (SSI) at the index level. These included 9 removals, 1 reoperation, and 1 supplementary fixation. 5 of the removals were associated with osteolysis, with confirmed or suspected infection reported for all 5 subjects. The mean timeframe for removal for osteolysis was 73 months post-op (range 54–86 months). The mean timeframe for SSI for other causes was 35 months (range 1-77 months).

Conclusion : The reduction in disability and pain associated with M6-C in earlier follow-up periods are maintained at 7 years post-op. 7-year SSI rates are comparable to other commercially available artificial discs. The safety and performance of M6-C in this cohort will continue to be monitored out to 10 years post-op.