159. Midterm 4-year outcomes for single-level total disc replacement with a novel viscoelastic artificial cervical disc compared to ACDF

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 and has previously demonstrated favorable clinical outcomes out to 2-years post-implantation. PURPOSE To evaluate the safety and effectiveness of the M6-C artificial cervical disc compared with ACDF. STUDY DESIGN/SETTING A prospective, multicenter, controlled, IDE clinical trial is ongoing. Twelve M6-C sites and 11 ACDF sites are participating in the study, with preoperative assessments followed by assessments at 6 weeks, 3 months, 6 months, 1 year and annually out to 10 years postimplantation. PATIENT SAMPLE Study subjects presented with one-level symptomatic degenerative cervical radiculopathy, and received either M6-C or ACDF at a single level. OUTCOME MEASURES Neck Disability Index (NDI), neck pain and shoulder/arm pain visual analog scale (VAS) scores. Methods The M6-C and ACDF cohorts were propensity matched. Follow-up assessments are ongoing and planned out to 10-years postop. Results A total of 160 M6-C and 189 ACDF subjects were enrolled. NDI scores are available for 124 M6-C and 148 ACDF subjects at 3 years, and 116 M6-C and 133 ACDF subjects at 4 years postop. At 3 years postop, M6-C subjects had a mean NDI score of 10.9 - significantly better than the mean of 17.2 observed in the ACDF group. A significant difference was observed at 4 years postop (M6-C mean of 10.3 compared to 19.2 for ACDF.) M6-C subjects experienced a mean improvement from baseline of 43.9 points at 3-years and 45.2 points at 4-years postop, compared to 36.0 and 36.0, respectively, for the ACDF cohort, with the 4-year results being significantly better for the M6-C group. More M6-C subjects experienced a 15-point improvement from baseline (93.6% at 3 years and 95.7% at 4 years,) compared to the ACDF cohort (86.6% and 82.7%, respectively,) with the 4-year results being significantly better for the M6-C group. Neck pain and shoulder/arm pain VAS scores are available for analysis for 124 M6-C and 148 ACDF subjects at 3 years, and 116 M6-C and 134 ACDF subjects at 4 years postop. At 3 years postop, M6-C subjects had a mean neck pain VAS score of 1.1, which was significantly better than the mean of 2.0 observed in the ACDF control group. Similarly, a significant difference was observed at 4 years postop (M6-C mean of 1.0 compared to 2.3 for ACDF.) M6-C subjects experienced a mean improvement from baseline of 6.1 points at 3-years and 6.2 points at 4-years postop, compared to 5.2 and 4.8, respectively, for the ACDF cohort, both significantly better for the M6-C group. Similarly significant results were observed in shoulder/arm pain VAS scores (worst side) at 3-years (0.9 for M6-C and 2.2 for ACDF) and 4-years postop (0.6 for M6-C and 2.7 for ACDF.) One M6-C subject (0.6%) had the device removed in the first 4 postop years (chronic neck pain.) Conclusions The significant benefits in NDI and neck pain and shoulder/arm pain VAS scores associated with M6-C in earlier follow-up periods, compared to ACDF controls, appear to be maintained at 3- and 4-years postop, with no concerns for durability of the surgical outcome or the prosthesis at 4 years. Both NDI and neck pain and shoulder/arm pain will continue to be monitored in this cohort via annual assessments out to 10-years postop. FDA DEVICE/DRUG STATUS M6 TDR (Approved for this indication)