41 - 6-year Outcomes for Single-Level Total Disc Replacement with a Novel Viscoelastic Artificial Cervical Disc

Background Context:
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.

Purpose:
To evaluate 6-year safety and effectiveness of the M6-C artificial cervical disc.

Study Design/Setting:
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.

Patient Sample:
Study subjects presented with one-level symptomatic degenerative cervical radiculopathy, and received either M6-C or ACDF at a single level.

Methods:
A prospective study of M6-C subjects. Follow-up is planned out to 10-years post-op.

Results:
At 6 years post-op, M6-C subjects had a mean Neck Disability Index Scores (NDI) score of 9.2. M6-C subjects experienced a mean NDI improvement from baseline of 46.6 points at 6-years. At 6 years post-op, 95.1% of M6-C subjects experienced a 15-point improvement in NDA score compared to the pre-operative assessment.

At 6 years post-op, M6-C subjects had a mean Neck Pain VAS Score of 1.0 (out of 10). M6-C subjects experienced a mean improvement from baseline of 6.2 points at 6-years post-op. Similar results were observed in Shoulder/Arm Pain VAS Scores (worst side) at 6-years, with a mean of 0.4 for M6-C, and a mean improvement from baseline of 6.8 for M6-C. 91.2% of M6-C subjects experienced a mean improvement of 2.0 or greater in Neck Pain VAS, compared to baseline, and 96.1% of M6-C subjects experienced a mean improvement of 2.0 or greater in Arm Pain VAS (worse side,) compared to baseline

Through 6 years post-op, 7 of the 160 M6-C subjects experienced Supplemental Surgical Interventions (SSI) at the index level. These included 5 Removals, 1 Reoperation, and 1 Supplemental Fixation. Of the removals, 2 were performed due to persistent neck and arm pain (with 1 being replaced by a new M6-C,) and 2 were performed due to osteolysis associated with a confirmed infection. One removal was performed due to increasing posterior translation.

Conclusions:
The benefits in NDI and Neck Pain and Shoulder/Arm Pain VAS Scores associated with M6-C in earlier follow-up periods are to be maintained at 6-years post-op. When the M6-C was used at a single level, revisions for sterile osteolysis were not observed at 5-years post-op. The safety and performance of M6-C in this cohort will continue to be monitored out to 10-years post-op.