Prospective, multicenter clinical trial comparing the M6-C compressible cervical disc with anterior cervical discectomy and fusion for the treatment of single-level degenerative cervical radiculopathy: 5-year results of an FDA investigational device exemption study

BACKGROUND CONTEXT: Various total disc replacement (TDR) designs have been compared to anterior cervical discectomy and fusion (ACDF) with favorable short and long-term outcomes in FDA -approved investigational device exemption (IDE) trials. The unique design of M6 -C, with a compressible viscoelastic nuclear core and an annular structure, has previously demonstrated favorable clinical outcomes through 24 months. PURPOSE: To evaluate the long-term safety and effectiveness of the M6 -C compressible artificial cervical disc and compare to ACDF at 5 years. STUDY DESIGN: Prospective, multicenter, concurrently and historically controlled, FDAapproved IDE clinical trial. PATIENT SAMPLE: Subjects with one -level symptomatic degenerative cervical radiculopathy were enrolled and received M6 -C (n=160) or ACDF (n=189) treatment as part of the IDE study. Safety outcomes were evaluated at 5 years for all subjects. The primary effectiveness endpoint was available at 5 years for 113 M6 -C subjects and 106 ACDF controls. OUTCOME MEASURES: The primary endpoint of this analysis was composite clinical success (CCS) at 60 months. Secondary endpoints were function and pain (neck disability index, VAS), physical quality of life (SF -36, SF -12), safety, neurologic, and radiographic assessments. METHODS: Propensity score subclassification was used to control for selection bias and match baseline covariates of the control group to the M6 -C subjects. Sixty -month CCS rates were estimated for each treatment group using a generalized linear model controlling for propensity score. RESULTS: At 5 years postoperatively, the M6 -C treatment resulted in 82.3% CCS while the ACDF group showed 67.0% CCS (superiority p=.013). Secondary endpoints indicated that significantly more M6 -C subjects achieved VAS neck and arm pain improvements and showed maintained or improved physical functioning on quality -of -life measures compared to baseline assessments. The M6 -C group -maintained flexion -extension motion, with significantly greater increases from baseline disc height and disc angle than observed in the control group. The rates of M6 -C subsequent surgical interventions (SSI; 3.1%) and definitely device- or procedure -related serious adverse events (SAE failure; 3.1%) were similar to ACDF rates (SSI=5.3%, SAE failure=4.8%; p>.05 for both). CONCLUSIONS: Subjects treated with the M6 -C artificial disc demonstrated superior 5 -year achievement of clinical success when compared to ACDF controls. In addition, significantly more subjects in the M6 -C group showed improved pain and physical functioning scores than observed in ACDF subjects, with no difference in reoperation rates or safety outcomes. (c) 2023 The Authors. Published by Elsevier Inc.