Cervical disc arthroplasty (CDA) has been available in the United States for over a decade. However, it has not been widely adopted despite multiple IDE RCTs that have reported better results than ACDF. Dr. Lavelle and colleagues published the 10 year follow-up data on the RCT comparing the BRYAN cervical disc to ACDF for single level pathology in the May 1 issue. Over 450 patients were originally randomized to either CDA or ACDF using an anterior plate and allograft, and approximately 50% were available for 10 year follow-up. At enrollment, the average age was 45, all patients had radiculopathy or myelopathy, and patients with significant spondylosis, collapsed disk space, kyphosis, or facet arthropathy were excluded. The primary endpoint was "overall success", which required a greater than 15 point improvement on the Neck Disability Index (NDI), no decline in neurological function, no serious adverse events related to the implant, and no subsequent surgery at the index or adjacent levels. At 10 years, 81% of CDA patients and 66% of ACDF patients achieved "overall success" (p=0.005). The CDA group also improved about 7 points more on the NDI (38 points vs. 31 points, p=0.01). Neck and arm pain VAS scores also favored CDA, though the differences were not significant. The authors did not report the overall reoperation rates for the two groups, though they noted there was a trend towards a lower reoperation rate for adjacent segment disease in the CDA group (10% vs. 16%, p=0.15). They reported 6 reoperations for pseudarthrosis in the ACDF group and 3 device removals in the CDA group related to implant complications. The serious device-related adverse event rate was 4% for the CDA group and 5% for the ACDF group.
This study represents some of the best long-term data available on CDA. The results were similar to the short and medium term studies that showed modest benefits for CDA compared to ACDF. Like most long-term studies, this one is limited by loss to follow-up, which puts the study at risk for attrition bias. However, loss to follow-up was similar for the two groups, and it seems unlikely that those lost to follow-up were markedly different for the two treatment groups. The authors could have supported this hypothesis by analyzing the characteristics of the patients lost to follow-up in each group. They could have more clearly reported the reoperations in each group, as it is somewhat hard to determine the overall reoperation rates from the data provided. A major question about CDA is why it has failed to gain popularity despite promising trial results. The inclusion and exclusion criteria used in this study may explain the low rates of adoption. The enrolled patients were young, had single level disease, and no significant spondylosis. The vast majority likely had acute, soft disk herniations. This type of patient is relatively rare in most spine practices, with the majority of radiculopathy and myelopathy patients presenting with multilevel spondylosis with central and foraminal stenosis due to disk osteophyte and uncovertebral hypertrophy. These patients would not have been included in this study, and most surgeons consider that type of pathology a contra-indication to CDA. It may be that most spine surgeons do not see enough patients who are appropriate candidates for CDA to dedicate the time and energy to learning the technique and progressing along the learning curve required for its use. There is also concern about the very long-term outcomes for these devices, given that they tend to be indicated in relatively young patients. In this study, the average patient will likely live an additional 35 years or more, and it is unclear what will happen to these devices over decades. Most total joint replacements have a substantially shorter lifespan than the patients in this study. Finally, the advantages of CDA are relatively modest compared to ACDF, even in the highly selected populations enrolled in the industry-sponsored IDE trials. The patient reported outcomes are similar for CDA and ACDF, and the decrease in adjacent segment disease is relatively minor. While CDA does seem safe and effective, it is unclear if it will ever be widely adopted.
Please read Dr. Lavelle's article on this topic in the May 1 issue. Does this change your views about cervical disc replacement? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor