Zeitschrift für Wirbelsäulen- und Neurochirurgie

One-Year NDI and VAS Outcomes from the Single-Level PEEK-on-Ceramic SimplifyTM Disc FDA IDE Trial

Fred H Geisler, David G Maislin, Brendan T Keenan and Greg Maislin

This study was performed to evaluate the early clinical results at one year for the Simplify™ Cervical Artificial Disc. We compared outcomes for 150 Simplify Disc subjects at one-year followup in a prospective, multicenter, FDA IDE clinical trial with 119 propensity score matched historical control subjects who received conventional anterior cervical discectomy and fusion (ACDF) for single-level cervical degenerative disc disease. The outcome measures included the change from preoperative baseline to one-year in Neck Disability Index (NDI) and visual analog scales (VAS) for neck and arm pain, with scores for the few missing oneyear follow-up implicitly imputed using mixed models for repeated measures (MMRM). The MMRM was used to estimate within group and between group differences controlling for propensity score subclass and the relevant baseline value. The adjusted mean changes (and standard errors) in NDI from baseline to one year were -46.7 (SE=1.7, p<0.001) and -38.1 (SE=1.9, p<0.001) for Simplify Disc subjects and ACDF control subjects, respectively. The adjusted Simplify Disc vs. control difference in mean NDI change at one year was -8.7 (SE=2.7) with p=0.002; the 95% confidence interval for the mean difference was -14.0 to -3.3. The adjusted mean changes in VAS neck and arm pain from baseline to one year were -62.4 (SE=2.0, p<0.001) and -55.2 (SE=2.3, p<0.001) for Simplify Disc and ACDF controls, respectively. The adjusted Simplify Disc vs. control difference in mean VAS neck and arm pain change at one year was -7.3 (SE=3.3) with p=0.029 (95% CI -13.8 to 0.8). Therefore, it can be concluded that the one-year clinical results of the Simplify Disc are superior to ACDF for both 1) improvement of NDI and 2) improvement in VAS neck and arm pain. Inspection of all eight prior FDA cervical total disc replacement studies indicates that these good results for the Simplify Disc can be expected to continue for five years and beyond, but longer term follow-up is necessary for verification.