I still laugh (internally) when a new patient comes to my office and right off the bat tells me, their neurosurgeon, that they need spinal surgery. That is a huge red flag for me and typically these are the patients that absolutely do NOT need surgery. To be fair, most patients are relieved when I explain that they aren’t going to need an operation on their spine. There are some patients, however, who are legitimately upset with me when I don’t offer surgery! I get it, they have likely been dealing with severe back pain for quite some time and they’re desperate. They want a fix. Ultimately, though, my job is to prevent patients from having a surgery that isn’t going to help them.
Why does surgery on a bulging disc not fix back pain? Before we answer this let’s discuss what it means when a disc is bulging. We’ve talked extensively here at Spinal(con)Fusion about degenerative disc disease. For quick review, as an intervertebral disc (IVD) ages, a cascade of inflammatory mediators is released that causes degeneration of the disc. In early phases of disc degeneration the IVD loses water content and becomes dehydrated (this give is a characteristic black appearance on MRI, see figure 1.) Further inflammatory changes cause a loss of structural integrity of the disc and it starts to collapse resulting in circumferential bulging of the annulus fibrosus-the dreaded bulging disc. So a bulging disc is a disc that is degenerating. Here’s what’s interesting: this process shouldn’t be painful because the IVD doesn’t have any inherent nerves that carry pain sensation. It becomes painful because as the disc degenerates the same inflammatory mediators that cause degeneration also recruit new pain fibers to carry pain sensation to the dorsal root ganglion of the nearby nerve. The degenerating IVD is rewired to perceive pain that it couldn’t perceive before. After this rewiring process, any movement of the degenerated disc then causes severe pain.
Figure 1: T2 MRI shows so-called “black disc” at L5/S1; note the bulging annulus (pink arrow.) A normal disc is seen at L4/5 with normal water content (as indicated by its brightness) and normal annulus (blue arrow.)
So why not just clean out the degenerated disc and surgically fuse the two vertebral bodies together? If you eliminate the motion at the degenerated disc then the pain should be relieved right? I wish it were that simple. Often when lumbar fusions are done for back pain caused by DDD alone the patient is no better. We don’t exactly know why immobilizing the diseased motion segment doesn’t relieve the pain but it probably has to do with the way the disc has been rewired to perceive pain. Once that rewiring occurs the nervous system may learn the pain so that no surgery will ever be able to relieve it. Unfortunately I think that there are surgeons out there who don’t understand this process and continue to perform lumbar fusions on patients with so-called “black discs.” I am not one of those surgeons. In my opinion lumbar fusion surgery should NOT be performed for degenerative disc disease (DDD) alone as often the patient is no better after the procedure.
One caveat: in cases of severe DDD the patient can also develop complete collapse of the disc space, severe arthritis in the corresponding facet joints and Modic changes in the adjacent vertebral bodies (see figure 2.) These multiple degenerative changes (i.e. not JUST DDD) collectively indicate to me that the entire motion segment has become structurally incompetent. This structural instability can lead to so-called mechanical back pain. If a patient has exhausted all conservative measures and is still having severe pain I may offer surgery in these rare cases.
Figure 2: T1 MRI shows severe DDD at L4/5 with severe disc space collapse (pink arrow) and Modic changes in adjacent vertebral bodies (blue arrows.) Such severe DDD would also be expected to cause severe arthropathy in the corresponding facet joints. Source: Rahme et al, 2008.
Remember: leg pain is different than back pain. In our next post we’ll discuss how surgery can be helpful for patients with LEG pain caused by a bulging or herniated disc.
Thanks for reading and Happy Holidays!
J. Alex Thomas, M.D.
1. Rahme R, Moussa R: The modic vertebral endplate and marrow changes: pathologic significance and relation to low back pain and segmental instability of the lumbar spine. AJNR Am J Neuroradiol 29:838–42, 2008.