Lumbar total disk replacement (TDR) was developed with the goal of treating chronic low back pain due to disk degeneration while decreasing the rate of adjacent segment degeneration (ASD) associated with fusion. While this technology was introduced many years ago, we still do not know if TDR has lived up to its promise. Multiple industry sponsored trials have compared TDR to various fusion technologies (i.e. anterior lumbar interbody fusion with threaded cages and circumferential fusion), usually with a noninferiority design. In an attempt to synthesize the results of these heterogeneous studies into clinically meaningful data, Wilco Jacobs and his colleagues from the Netherlands performed a formal meta-analysis for the Cochrane Review. They included six industry sponsored trials comparing TDR to various types of fusion as well as an independent trial comparing TDR to a structured rehab program. They concluded that TDR was associated with a statistically significant benefit for low back pain, the Oswestry Disability Index (ODI), and patient satisfaction. However, the differences for low back pain and ODI were smaller than the predefined thresholds for clinical significance, suggesting that TDR and fusion had similar clinical outcomes out to two years. Somewhat surprisingly, most of these studies did not evaluate ASD, the main problem that TDR was supposed to alleviate.
These results led to the authors concluding that lumbar TDR did not result in a clinically significant benefit compared to fusion out to two years following implantation. Given the hypothetical potential for increased long-term complications associated with TDR compared to fusion (i.e. mechanical failure, osteolysis, etc.), the authors suggested cautious adoption of the technology until long-term results are in. The real question is not whether or not TDR leads to better results than fusion but if chronic low back pain associated with disk degeneration is a surgical problem. While some chronic low back pain patients clearly improve with fusion or TDR, many of these patients also improve with structured rehab, making it difficult to select patients who will do better with surgery compared to nonoperative treatment. Given the current state of the literature on the topic of surgery for chronic low back pain, future studies should probably focus on defining the optimal surgical patient rather than on the optimal surgery. This meta-analysis also nicely demonstrated that the industry sponsored studies generally failed to study ASD, a serious methodological shortcoming given that was the complication TDR was designed to reduce. One of the studies did evaluate ASD at five years and concluded that the TDR significantly reduced the rate of radiographic ASD, though it did not detect any clinically significant differences in clinical outcomes at five years.1 Like many attempts at meta-analysis in the spine world, this one likely identifies more questions than it answers. Hopefully future studies will help determine the appropriate chronic low back pain surgical candidates for either TDR or fusion. Once we can do this successfully, we will have to determine if TDR or fusion is the better operation and identify the long-term issues associated with TDR.
Please read this article in the January 1 issue as well as the accompanying commentary. Does this Cochrane Review change how you view lumbar TDR? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor
1. Zigler JE, Glenn J, Delamarter RB. Five-year adjacent-level degenerative changes in patients with single-level disease treated using lumbar total disc replacement with ProDisc-L versus circumferential fusion. J Neurosurg Spine 2012;17:504-11.