Disc Replacement for Low Back Pain, what's the evidence?

Disc Replacement for Low Back Pain, what's the evidence?

In a prior article, we discussed the use of intervertebral disc replacements for the treatment of neck pain. Please take a look at that article for more details. In short, it is a surgical alternative to discectomy (removal of disc) and fusion in treatment degenerative disease (osteoarthritis) of the neck that has failed conservative treatment. Early studies showed comparable results between the two procedures but further studies are needed to see whether there is any benefit to disc replacement.

The concept of disc replacement actually got its start in the lumbar spine (low back).

The initial proposed indication for lumbar disc replacement was degenerative disc disease of the lumbar spine, a medical term for osteoarthritis of the lower back. The proposed upside is that unlike a lumbar fusion, the disc replacement preserves motion in the operated on segment. One of the issues with lumbar fusions is that once a single lumbar level is fused the mechanical stress is displaced to adjacent segments, and these segments begin to degenerate as well. This happens at a rate of approximately 2.5% per year. However, the issue is slightly more complicated and is not fully explained by increased mechanical stress on the adjacent segments.

A certain proportion of people will develop degenerative disease at multiple levels, regardless of whether anyone of them was operated on. This suggests that not all adjacent segment disease is the result of a fusion.

The second confounding factor is that the additional mechanical stress on adjacent levels is only present if the total motion of the spine remains the same if the spine moves proportionally less after a single level has been fused then the mechanical stress on adjacent levels is not necessarily increased.

This is a complicated topic, and the take-home point is that a lot of further research is needed to understand adjacent segment disease better.

Disc Replacement Research

Disc replacement aims at improving the rates of adjacent segment disease, in hopes that preserving motion leads to less stress on adjacent levels. A randomized controlled study in 2012 looked at 5-year results of 161 total disc replacements and 75 fusions performed in patients with degenerative disc disease of the lumbar spine. This study showed that both groups showed significant improvement in terms of pain and function from baseline at 5 years. The study reported results at 2 years and at 5 years. There was no statistically significant difference between the two groups. Unfortunately, the study does not report on the rates of adjacent segment degeneration, which would arguably be the most informative outcome.

This study suggests that lumbar disc replacement is “non-inferior,” meaning at least as good, as a lumbar fusion in providing pain relief and improving function.

It did not address the key question of whether there is less adjacent segment disease when a disc replacement is used. There have been no studies to date that suggest that disc replacements lead to less adjacent level disease, which was a key motivator for their invention. The other limiting factor of this study is that it looks specifically at patients with single level disease. Most commonly patients present with disease at more then 1 level, and it is difficult to predict how a disc replacement would perform in that scenario.

Another study looked at the use of a lumbar disc replacement for two-level degenerative disease of the lumbar spine. The study randomized 256 people to fusion versus disc replacement and followed these patients for 2 years. The total disc replacement group seemed to perform the same or better in terms of pain relief and function improvement throughout the 2 year time period. It is important to remember that these studies aren’t perfect and are performed by the individuals who designed the prosthesis and have a vested interest in seeing this technique succeed. However, we should also not discount the quality of the studies while taking into account potential bias.

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