Question: In patients with symptomatic cervical disc disease, what is the safety and efficacy of the ProDisc-C total disc replacement system (Synthes, West Chester, PA) compared with anterior cervical discectomy and fusion?
Design: Randomized (allocation concealed), blinded (patients), controlled, noninferiority trial with 24-month follow-up (U.S. Food and Drug Administration [FDA] investigational device exemption study).
Setting: 13 investigational sites in the United States.
Patients: 209 patients between 18 and 60 years of age (mean age, 43 y; 55% women) with symptomatic cervical disc disease causing intractable, debilitating radiculopathy from 1 vertebral segment between C3 and C7. Patients were also unresponsive to nonoperative treatment for =6 weeks and had a neck disability index (NDI) score of =30%. Exclusion criteria included =1 vertebral level requiring treatment, marked cervical instability on resting lateral or flexion-extension radiographs, allergies to materials used in the procedures, previous surgery at the level to be treated, infection, spondylosis, Paget disease, severe diabetes mellitus, rheumatoid arthritis, osteoporosis, systemic disease, active malignancy, and pregnancy. Follow-up was 96.5%.
Intervention: Patients were allocated to receive ProDisc-C implantation (n = 103) or standard anterior cervical discectomy and fusion (n = 106). The ProDisc-C procedure involved inserting the implant into the prepared channels after discectomy. The correct size and placement were determined by placing trial implants into the disc space until the appropriate implant footprint, disc height, and position were achieved. For standard anterior cervical discectomy and fusion, allograft bone spacers were used and an anterior cervical fixed-angle plate was placed over the graft and secured.
Main outcome measures: Overall success rate was determined by 4 component end points: NDI success (>15-point improvement from baseline), neurological success (maintenance or improvement in each sensory, motor, and reflex function evaluation), device success (no revision, removal, or reoperation of the implant or supplemental fixation), and adverse event success (absence of adverse events related to the procedure). A difference of 10% between groups in overall success rate was used to establish noninferiority as defined by the U.S. Food and Drug Administration. An additional ad hoc analysis with use of 6 health-related quality of life (HRQOL) end points was done to establish superiority of ProDisc-C by evaluating the minimum clinically important difference (MCID) in HRQOL measures: NDI success, willingness to have the same surgery again, absence of device failure, absence of fusion (ProDisc-C group) or absence of pseudarthrosis (discectomy and fusion group), improvement in neck or arm pain score on visual analogue scale, and absence of strong narcotic or muscle relaxant use.
Main results: A significant difference favoring ProDisc-C was observed with regard to device success at 24 months (Table). No significant difference was observed between the ProDisc-C group and the discectomy and fusion group in NDI success, neurological success, or adverse event success (Table). For overall success, the criteria for noninferiority were met (Table). For the ad hoc analysis of HRQOL end points, overall success was found to be greater for the ProDisc-C group than for the discectomy and fusion group (Table), showing superiority of ProDisc-C (Table).
Conclusion: In patients with symptomatic cervical disc disease, the ProDisc-C total disc replacement system was not inferior to anterior cervical discectomy and fusion and was superior with regard to certain health-related quality of life outcomes.
Murrey and colleagues report on the treatment of 209 patients with cervical radiculopathy, comparing patients who had anterior cervical discectomy and fusion with allograft and plate fixation with those who had ProDisc-C insertion. Neurological success was 90.9% in the ProDisc-C group and 88% in the discectomy and fusion group.
One argument for the use of cervical discectomy relates to concerns about adjacent disc degeneration. The authors cite Hilibrand and colleagues1, who reported that 25.6% of patients would have development of new disease requiring surgical intervention at an adjacent level within 10 years after anterior cervical discectomy and fusion; however, the prevalence of adjacent level disease was 19.2% at 10 years. Of those patients, only 27 required a second operation, giving an overall reoperation rate of 13.8%. This study did not follow patients long enough to determine the risk for adjacent disc degeneration, but it must be noted that progression of degenerative disc disease can occur in up to 50% of the population by the fifth decade.
Overall, repeat surgery was required by 9 patients in the discectomy and fusion group and by 2 patients in the ProDisc-C group. However, in the discectomy and fusion group, only 1 patient required repeat surgery for adjacent level degenerative disease, whereas the remaining 8 patients required repeat surgery because of plate complications and pseudarthrosis. Therefore, I believe we should continue to question the technique of using allograft and plating because autograft with or without plating has historically had a much higher fusion rate.
At present, there seems to be no advantage of the ProDisc-C system over traditional anterior cervical discectomy and fusion.
Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am.1999;81:519-28.81519
1999
[PubMed]
Author's Response:
The conclusion in the commentary states "At present, there seems to be no advantage of the ProDisc-C system over traditional anterior cervical discectomy and fusion." It should be noted that the study was specifically designed as a noninferiority study, not a superiority study. As such, the study could not prospectively prove an advantage. The study did show safety and efficacy at least equivalent to that of anterior cervical discectomy and fusion.