Abstract
Introduction
ProDisc-C (Synthes Spine USA Products; LLC, West Chester, PA) began its FDA Investigational Device Exemption multicenter randomized study in 2003 and has received marketing approval by the FDA in 2007. This study reports final results of the 7-year follow-up.
The aim of this study is to compare long-term efficacy and safety of single-level cervical arthroplasty using ProDisc-C (DePuy-Synthes, Inc) to anterior cervical discectomy and fusion (ACDF) in patients with symptomatic cervical disk disease.
Materials and Methods
Between August 2003 and January 2005, 209 patients with symptomatic single-level cervical degenerative disk disease refractory to conservative management were enrolled in a prospective, randomized, controlled trial. Of these, 103 received ProDisc-C and 106 ACDF. Patients were followed up for 7 years. The outcomes included Visual Analog Scale for Arm and Neck Pain, Neck Disability Index (NDI), MOS-Short Form 36 (MOS-SF36), neurologic success, adverse events related to the surgery, and secondary surgeries. At the final follow-up at 7 years, the overall follow-up rate was 79.0%.
Statistical Analysis
Discrepancies between the groups in preoperative demographics and postoperative outcome valuations were analyzed using the Fisher exact test for the categorical variables, and the t-test for the continuous variables. The changes in outcome scores at 2 and 7 years were analyzed using two-way repeated measurements analysis of covariance (ANCOVA) with one fixed factor (“GROUP”) (ACDF and ProDisc-C), one repeated factor (“TIME”) with two levels corresponding to two follow-up times (2 and 7 years), as well as the interaction effect between the GROUP and the TIME factors. Differences in proportions of secondary operations on the index surgical levels were analyzed by Fisher exact test. In the case of multiple secondary surgeries, each subject was counted only once. The time until the secondary surgery was analyzed by Kaplan-Meyer survival estimates, and the differences in survival tested by log-rank test.
Results
Table 1 shows adjusted means and their confidence intervals by treatment group. All outcomes improved compared with preoperative status in both study arms at 2 years (p < 0.05), except for the SF36 General Health (p > 0.05). At 7 years postoperative, the improvements were maintained for the same variables as at 2 years postoperative (p < 0.05). There were no significant differences between the ACDF and ProDisc-C patients in the extent of the improvement (GROUP effect p > 0.05 for all variables) for any outcome variable. Further, there were no differences in the extent of improvement between 2 and 7 years postoperative (TIME effect p > 0.05) for all outcome variables. Finally, there were no differences in the time course changes by the group at 2 and 7 years (GROUP*TIME interaction p > 0.05) for any outcome variable. Neurological success rate at 2 years was 88.0 and 90.9% in the ACDF and ProDisc-C groups, respectively (p > 0.05). At 7 years, the success rate was 88.9 and 87.7%, in the ACDF and ProDisc-C groups, respectively (p > 0.05). At 7 years postoperatively, 11.3% subjects in ProDisc-C group had evidence of bone bridging at index level.
Of the 106 subjects in the ACDF group, 16 (15.1%) subjects required a secondary operation at the same level compared with 6 out of 103 (5.8%) in the ProDisk-C group (p = 0.0410). Of six secondary surgeries in the ProDisc-C group, three were for device removal, one for reoperation, and two for revision. In the ACDF group, there were six removals, one reoperation, nine revisions, and three supplemental fixations. The reoperation-free survival time was better in the Pro-Disc-C compared with ACDF patients (log-rank p = 0.0221). The conditional incidence rate ratio for the secondary surgery was 3.09 (95% CI, 1.27-8.45, p = 0.0112).
There were 6 surgeries in 6 subjects that involved adjacent levels in the ProDisc-C group, compared with 22 surgeries in 13 subjects in the ACDF group. The p-value for the subjects with any surgery at the adjacent level was 0.1134 and the p-value for surgery events was 0.0029
Conclusion
Both ACDF and cervical arthroplasty with ProDisc-Care associated with significant long-term improvement in relevant symptoms, functional and health-related quality of life outcomes. There is no evidence of differential efficacy between the two treatments. Disc arthroplasty with ProDisc-C is associated with a significantly lower risk of secondary operation at both the index and adjacent surgical levels.
M. Janssen: Conflict with Depuy Synthes
B. Kopjar: Conflict with Smith & Nephew, Cerapedics, AO Foundation
J. Zigler: Conflict with Depuy Synthes
J. Spivak: Conflict with Depuy Synthes—Prodisc Teaching, Depuy Synthes—Prodisc Publications Committee Member
D. Murrey: Conflict with Amedica, OrthoMedFlex, Stryker