Hi, I am Dr. Tony Mork, author, speaker, inventor and endoscopic spine specialist.
Today I would like to talk about the problem of lumbar foraminal stenosis. I am going to divide this topic into two videos. So in the first video, I am going to talk about the problem of lumbar foraminal stenosis, what it is, where it is, and why it can cause pain. In the second video, I am going to talk about treatment; and you will understand the treatment options a lot better if you understand what the problem really turns out to be.
Why lumbar foraminal stenosis can hurt you?
OK, let’s get started: Let’s talk about lumbar foraminal stenosis and why it can hurt you. Well, what is the problem, and why does it hurt you? The problem is narrowing of the foraminal canal, which is sometimes referred to as stenosis. This narrowing causes pinching of the exiting nerve root as it passes from the spinal canal out to your buttock, thigh, legs, or feet. Talking about the foraminal canal, where is it anyway? What does it look like?
Here we can see the lumbar spine from the side; and what I want to point out is that the foraminal canal really is shaped like a keyhole. In a moment I am going to show you what the bordering structures are of the keyhole, but the idea is that it is a keyhole type of structure. In this particular picture, I have removed the nerve root, which you can see above and below this, but the foraminal canal (circled in orange) is shaped like a keyhole.
Next we are going to take a look and see what this looks like on an MRI scan. Here we see the identical pictures noted previously, except this is an MRI scan. Again, it shows a keyhole type of a structure with a darker nerve root or what I call an eyeball in the center. The eyeball is surrounded by a white layer, which is fat, but this is what the foraminal canal looks like in the normal situation in the spine on an MRI.
In this picture, we are going to take a look at the borders of the foraminal canal in the lumbar spine. The first border is the disc. So we can see that if the disc is herniated out here, into the foraminal canal, that this would contribute to a space-occupying issue. Here is the vertebral body below, and we can see that off of it comes the ascending facet. So this structure is the ascending facet. The tip here is the notorious superior articular process or SAP, and this nerve is removed right here, so it is a little bit difficult to interpret; but if we go look at the level above, you can see where this piece of bony edge could dig into this nerve root as it exits the foraminal canal.
OK, we have the disc, we have the ascending facet. Over here we have the descending facet, and between this facet descending and this one ascending is actually the facet joint. If the facet joint was expanded or the soft tissues from this, we could see that a synovial cyst, for example, could come out here and also be a space-occupying lesion in the foraminal canal as well.
OK, here is an MRI scan that we just reviewed on the model. Let me just review the keyhole, foraminal canal, which is right here. Inside it is the eyeball, or what is the nerve. It kind of looks like an eyeball, and it is surrounded by the white, which is the fat. This is the disc; the dark band here is the disc, and we can see that if you had a foraminal disc herniation that could push out into here. This is the ascending facet, the notorious, almost like a guillotine-like superior-articular process; and you can actually see it exerting some pressure in here already. We have the descending facet over here. So this is how it would look like on an MRI scan.
What is the exiting nerve root?
We are going to talk a little bit about the exiting nerve root, which branches off the spinal cord and exits out of the spinal canal via the foraminal canal, which is what we are talking about today. Just remember that after the nerve passes out of the foraminal canal, it then goes unobstructed and free down to the buttock, thigh, leg, or foot; and it can provide sensation and motor function.
Here we are looking at the spinal canal from the back, and we can see that the spinal cord is going down, and at a certain location a nerve root is coming off the spinal cord and exiting via the foraminal canal. Here we can see the spinal cord. We have tilted the spine or rotated it just a small amount, but we can see that the spinal cord is here. The yellow arrow is pointing to the nerve root as it is exiting off the spinal cord, and here we can see the notorious superior-articular process as a place that can actually indent the exiting nerve root. So the superior-articular process of the ascending facet is really a major problem, and I am going to be showing you some videos of the treatment and how we actually get rid of this. But this is one of the major contributing problems here.
This is a quick review of the borders of the foraminal canal, being the disc, the superior-articular process of the ascending facet, the descending facet, and then the actual soft tissue capsular tissues of the facet joint which sit between the ascending and descending facet.
Remember that there is a specific nerve that will be exiting each foraminal canal, and the pain or numbness or weakness will correspond to that nerve that is passing out of the foraminal canal. For example, L4 is usually associated with problems in the front of the thigh; L5, typically with the outside of the buttock and the outside or lateral side of the thigh and calf; S1 to the back of the calf. This is just a reminder that really in many ways, looking at the nerves as they come out of the spinal canal and go down to your legs, is really like an electrical wiring diagram.
Several Causes and Symptoms of Foraminal Stenosis
The feelings and sense of pain and numbness is fairly consistent as the nerves exit the spinal canal through the foraminal canal and then out to your extremities, etc.
- Pressure on the nerve can result in:
- Numbness, which includes needles and pins.
- Or weakness and atrophy.
An example would be a footdrop that occurs when there is too much pressure on the L5 nerve root coming out of the foraminal canal.
There are several things that can cause pinching of the nerves that exit including the bone:
- A bone spur
- A disc herniation
- Soft tissues
- Overgrowth of a synovial cyst
- The actual tissues from the facet joint capsule
- Or a combination of any of the above.
Here is an example of an abnormal foraminal canal. So let me just take a look and show you what things should normally look like. Here we have a keyhole foraminal canal. We can see fat around the nerve root right here, even though we have a narrowed disc space, with a little bit of disc herniation into the foraminal canal. We still enough fat to think that there is probably no particular problem here. Let’s compare this to the abnormal level below. Here we have the disc, which is darker stripe. There is some herniation in the foraminal canal. The nerve is definitely squashed here, and it is being caught between the disc, and this dark is the soft tissues of the facet joint. So here we have the ascending facet, the notorious superior-articular process here, and then we have an expansion of the capsule of the facet joint. But you can see that it is squashing this nerve, causing symptomatic foraminal stenosis.
This is just a reminder that loss of the disc height can aggravate foraminal stenosis, and actually the reverse of this process, where you increase the disc height, is also one of the keys of using a fusion or an implant to open up the disc height in order to relieve foraminal stenosis, whether in the lumbar or the cervical spine.
Here is an unusual example of foraminal stenosis occurring after a fusion. So people oftentimes assume that nothing happens after a fusion, but it is not really the case. Here is a gentleman who came in several years after a fusion with a very symptomatic lower extremity. He did not want a revision of his fusion, and we could see exactly where the problem was. This is a spur coming off and is sticking right into the nerve root. So he was very symptomatic, and once this spur had been removed, he went back to being completely pain free. But you can see that he did not want to go through this, and really there is no need to when you can just open this up and trim this out, the spur alone with an endoscopic type of procedure.
Just remember that anything that changes the dimension of the foraminal canal can cause the symptoms of foraminal stenosis and nerve pain. So whether it is the tip of the facet, the superior-articular process intruding or sticking into the nerve; whether it is the soft tissues from the facet joint taking up space; whether there is a disc herniation or what they call a foraminal disc herniation; a spur like we saw; or loss of disc height of the disc space; anything that contributes to narrowing the canal can give rise to foraminal stenosis and its symptoms.
How to stop the pain or weakness from symptomatic foraminal stenosis?
It seems it should be relatively straightforward – get the pressure off the nerve. But there are some challenges, and the challenges are that it is a fairly small tunnel anyway, and you have a choice. You can kind of go from the outside in, or the inside out. Also, the offending structures that we have seen are relatively small, just maybe a small disc herniation or a small spur, even some overgrowth of the facet capsule, all really relatively small problems. But the nerve is subject to injury as well, so sometimes if you put an instrument in to actually decompress the nerve, it can actually momentarily at least contribute to the problem. So these are some of the challenges when thinking about solving foraminal stenosis.
Stay tuned to find out more about the treatment of lumbar foraminal stenosis in the next video.