There remains considerable controversy on the nature of Adjacent Segment Degeneration after lumbar fusion. To the non-spine surgeons, the issue is the theory that a fusion operation places more stress on the levels above or below the fusion, and will lead to accelerated degeneration and subsequent surgery. In fact, most surgeons will tell patients about the risk for potential future surgery after lumbar fusion.
The skeptic will say the surgeon is just setting up a biase towards future surgery. Some will say lumbar fusions are not great surgery, and the rate of future surgery is so great that the primary lumbar spine fusion surgery should be avoided. Several studies have showed a rate of additional future lumbar spine surgery after fusion at 10-15% over 10 years in the US population. Spine surgeons like me, need some guidance, so we can appropriately discuss the effects of lumbar spinal fusion, and the potential for increasing back pain, and subsequent surgery after the fusion.
Recently, there has been much interest in the so called Minimally Invasive Spine Surgery (MIS), and potential benefits of this approach in lumbar fusions. The major advantage, according to the researchers on MIS is the sparing of the lumbar multifidus muscle. It turns out the multifidus is probably the main stabilizing muscle of the spine, and preservation may indeed also prevent the development of the Adjacent Segment Degeneration associated with lumbar fusion.
The most relevant study regarding was recently published in the August 1, 2014 Spine, was the ISSLS Prize Winner and is titled “Long Term Follow-up Suggests Spinal Fusion is Associated With Increased Adjacent Segment Disc Degeneration But without Influence on Clinical Outcome: Results of a Combined Follow-up from 4 Randomized Control Trials” and authored by Anne F. Mannion, PhD, et al. To summarize, four sites, representing locations in the United Kingdom, Norway and Sweden followed patients for an average of 13 years randomized to surgery or non-surgery for painful lumbar disk degeneration. Pre-operative x-rays were obtained. The patients themselves had chronic LBP for more than a year, with the suspected cause of the pain secondary to degenerative disk disease. Inclusion criteria for the randomization included the use of several disability scales including the Oswestry Disability Index. Long term followup was obtained in 272 fusion patients, and 92 non-surgical patients. The results of the comparison of fusion vs non-fusion is another topic. This paper looked a the effects of fusions on development of Adjacent Segment Degeneration.
X-rays were compared between the groups. In both groups, there was development of disk space narrowing. In other words, with or without surgery, both groups had degeneration of the disks that were compared. The study also showed the disk narrowing of the surgical patients were of a great magnitude. But after statistical analysis, there were no evidence that the increased degeneration associated with the fusion patients led to any difference in clinical outcomes. In otherwords, the difference in the amount of degeneration between the fusion, and non surgery group did not cause any more disability or back pain. Based on the prospective nature of this study, I can conclude that adjacent Segment degeneration after spine surgery does not lead to more surgery secondary to the fusion. This may or may not be what Surgeons want to counsel, but it looks like it is the truth. Based on latest research, Surgeons can say Spine Surgery is always a possibility for any spine patient, but the need for additional surgery most likely is not related to a prior Lumbar Fusion.