Are Cervical Dermatomes Accurate?

The third thing that I was taught is that cervical dermatomes and myotomes are very reliable. So, the reason that we operate for radiculopathy coming down the arm is that we say it's very reliable, and you can, based on what muscles are weak, what fingers are numb, we can diagnose the level of the problem. And so if you can diagnose it, you can operate and you can get excellent results.

But this was a paper that was published by the group at Emory University recently and John Ree, who's the second author, was one of my former fellows. And what they published was that only 54% of their patients with a one-level radiculopathy actually followed the typical patterns of radiculopathy. So the vast majority of patients do not follow the Needder diagram.

Grams or the diagrams that we all learned of what the patterns are. So we all learned that, oh yeah, this, this is, uh, this area is C6, this is C7, this is C8, and if you've got the Pain or numbness in this area, this is what the dermatomes should be. But if you go back

And you actually study to see how did we get that information? We go all the way back to Forster, publishing in Brain in 1933.

And he did rhizotomies for patients who had cerebral palsy with spasticity or intractable Pain, and most of the Netter diagrams are based on Forster's diagram. You can see this is the Forster diagram and it looks a lot like the Netter diagrams.

Now let's see exactly how Forster did it.

Well, what he found was that if you just cut one nerve, let's say you cut the C6 nerve root.

Often he would get absolutely no deficit. The patients would wake up, there would be no weakness and no numbness. He realized that there was so much overlap of the dermatomes and even myotomes that just cutting one nerve would not do any, would not uh cause anything to be changed and the patient would still have symptoms. So he, what he would do is he would cut two nerves.

So if he wanted to find out what the C6 nerve root did, he would cut C5 and he would cut C7.

And then he would see what was left, and that's how he would determine what the C6 nerve root did.

Now, you would think that he did this on a lot of people in order to figure it out. No, it was 2 to 5 patients per level.

So, it's like saying that I'm gonna look at 2 to 5 people on this webinar, and I'm gonna look at, let's say Mark Aurelio, and I'm gonna look at me and I'm gonna say all human beings look like Mark Aurelio and me.

Well, we all know that people don't look like me.

And that every human being is unique. And yet we think that if we look at 2 to 5 cadavers and we just dissect that 2 to 5 cadavers, that that's how every human being is supposed to be. Well, that's ridiculous. Of course, it's gonna be inaccurate if you do it that way. There are a lot of overlap of dermatomes, so even cutting two nerves, sometimes you won't see much of a deficit.

And if you cut a nerve, the interesting thing is the brachial plexus reroutes the dermatomes and myotomes.

The interesting is, why doesn't it do it when you have a herniated disc? So if you herniated disc, the patient will have severe Pain and numbness and weakness. If you cut the nerve, a lot of the times there is no weakness, no numbness, and no Pain. It's because the body reroots around a, uh, a completely severed nerve where it may not be able to do that if the nerve is just impinged or if it is, uh, only, uh, partially damaged.

The Other thing is that you have to take into account how much time it took between cutting the nerve and mapping it, because if you cut the nerve and you map it months later or weeks later, the body will already have started to reroute and you may get a totally different picture.

The next person that we rely on for uh the Neder diagrams is another, you can see the Netter diagrams again in his. This is Keegan. Keegan and Garrett in 1948, they took a lot more patients now. They took 1300 patients. They took patients with a one-level herniated disc based on the myelography.

And what they did was they said, OK.

If you have a single-level herniated disc at C6-7 and you say this is what type of radiculopathy the patient had, they mapped it out. The problem was this myelograms often miss Pathology. So if you have a far lateral disc herniation, you can't see it on a myelogram. You need a CT scan and even a CT will miss the far lateral because the dura adheres.

To the nerve and there is no filling of the dye when you're out way out laterally and so far lateral disc herniation of the cervical Spine, you can't see on a myelogram, you can't see on a CT, you can only see on the parasagittal MRI images.

Now, out of that 1300, he only had 165 that were between C5 and T1.

Only 47 had a one-level problem at Surgery and all the Surgery were done posteriorly from laminectomies. So if you do a laminectomy, you're not gonna explore anteriorly in front of the disc. So if there's a disc in the front, and unless you do a, uh, an intradural uh operation where you cut the dentate ligament and you cut the ventral dura and you explore in the front to see if there's a herniated disc, you're never gonna find it with a laminectomy.

So, if there was a herniated disc at another level, he would have missed it. So obviously, this is not going to be a very accurate way to determine a single level herniated disc problem.

There are a lot of anomalous distributions. This was a patient that I treated years ago.

He had a C6-7 disc herniation. He had deltoid, biceps weakness, and numbness of the thumb and index finger. And I said,

That can't be the C6-7 level because the C6-7 would give you triceps and your fingers, either these two, this one, or these two, or these three fingers would be numb. And I said, I don't think the Surgery is gonna help you, but he was in so much Pain and he had so much uh uh problems with his weakness and uh with his numbness that I sent him for a transaminal nerve block.

And when I did it at C67.

Pain was instantly gone. I tried it at C4-5, nothing. Tried it at 5-6, nothing. 67, Pain was gone immediately. So I said, this isn't gonna help your weakness, it's not gonna help with the numbness because those are coming from different levels. It has nothing to do with your herniated disc at C6-7, but it's obvious that your Pain is coming from the C67 level. We took out the disc, the Pain went away, the numbness went away, and the weakness went away.

All instantly right after the Surgery, and I said,

This is impossible. How, how is this? Because I looked in every textbook and no textbook said that a C67 herniated disc could possibly cause numbness in these fingers or weakness in the deltoid and biceps. I said, that's just not possible. I just said, well, it must be a coincidence and forgot about it.

Years later, we looked at a barren cervical dermatomes and myotomes on patients that I had treated with a one-level disc herniation and patients that got better immediately after the Surgery, and we found that 61% had abnormal myotomes and dermatomes that didn't fit the meter diagrams.

12 had abnormal myotomes, 22 had abnormal dermatomes, and 3 had both abnormal dermatomes and myotomes. And it turns out that this is pretty common. The brachial plexus has tremendous variability. It's bilaterally asymmetric. The brachial plexus on the right looks different from the left in 40% of patients.

And many have a C4 contribution to the deltoid. So they have a prefixed brachial plexus where the C4 contributes to the deltoid. And some have a post-fixed brachial plexus where the T2 nerve root contributes to the brachial plexus. The brachial plexus is supposed to be C5, 678, and T1, but in some people it's 45678.

And in Other people, it's 567678 T1 T2.

And so it is highly, highly variable.

These are just some of the 29 different kinds of uh brachial plexus uh uh anomalies that people have discovered. There are at least 29 that have been described in the literature and this was about 4 or 5 years ago that I looked it up. I'm sure by now there must be 30, 40, 50 different uh types of brachial plexus anatomies that have been found in humans. And then once they have come out, the variations in how the brachial plexus move.

Is, is even greater. So if you look at how they come out and how they vary afterwards, there are thousands of different kinds of brachial plexus anatomies and probably.

No two people have the exact same brachial plexus anatomy that's the same on the left as on the right, which tells you that we were all taught to memorize a brachial plexus, draw it out, and we were all told to memorize it. But that's really a waste of time because if a professor right now would ask me, draw out the brachial plexus, I would tell the professor.

OK, there are about 5000 different variations of the brachial plexus anatomy that have been found. Which one of those 5000 would you like me to draw for you?

And of course, the professor would say, you're a smart alec, draw the one that's in the textbooks. And I say, but the textbook is wrong. The textbook assumes that there's one. It's like saying, draw me the picture of a human being, and I draw me, and I say, all human beings look like this, and we all know all human beings, thank God, don't look like this.

So, then after the brachial plexus comes out, there are all kinds of peripheral anatomical differences. a Martin Gruber anastomosis, where the median nerve goes into the ulnar nerve is there of almost half of the cases. And in these cases, you could cut the ulnar nerve and the patient has no deficits. That's how amazing anatomy is. A Marinacci communication, ulnar nerve to the median nerve. So if you cut the median nerve in these patients,

They have no deficits because the ulnar nerve also does the function of the median nerve, and there are a whole bunch of these things that have been described. So the problem is that there's so many different anatomical variations that you need to have a framework of how many people are, but that doesn't mean that you can say every human being is like that. You have to understand that there are variations, situs and versus.

All the organs that are on the left and the average person are on the right. In 1 in 100,000 people, the heart is on the right.

The liver is on the left, the stomach is on the right. Everything has been inverted with the situs inversus. So if you say the heart is always on the left, you would be wrong. In 1 in 100,000 people, you would be wrong. And if it's 1 in 100,000 people, they're gonna be several dozen people in the United States, several 1000 people in the United States, 100 people in the United States that have anomalous hearts that are on the right and instead of on the left.

So cervical dermatomes and myotomes are not as simple as we've been taught to believe that are in the textbooks. They are highly variable. And so that is yet another lie that they taught us. They weren't meaning to lie, it's just that, just, just didn't know. So the more you know about cervical anatomy, the more confusing it all gets.

Because then when you say you've got numbness here, how do you know it's supposed to be C6 as opposed to C7? Could it be C5 in a prefixed brachial plexus? Could it be both 5 and 6? Could it be 56, and 7? Well, the problem is that you cannot be positive anymore because now you know how anomalous the variations can be and how anatomy can be highly varied.

That's why what you have to do is you have to pay attention. You have to learn from your patients, and they say that I practice Medicine because I'm practicing, I'm learning constantly. So when a patient comes in and I see that they have a one-level disc herniation, I always ask them, where does it hurt?

Where in the neck does it hurt? Where in between the Shoulder blades does it hurt? Where in the arm does it hurt? Which fingers are numb? What part of the arm is numb? And I see the variations. C7, sometimes they say, oh, I'm numb here, sometimes I'm numb here, sometimes I'm numb in these two, in these 3, in these 4. The whole hand is numb in some people. Sometimes it's these two fingers, sometimes it's these 3, sometimes it's these 4 fingers, sometimes it's just one finger or the thumb, and I see the.

Amount of variation there is with just a single nerve root problem. And I learned from that and I understand that when somebody comes in with a single-level Pathology and they say the whole hand is numb, I used to think, oh, they're faking it or they're crazy, or they must have something else going on. Now I know that yes, I still look to make sure they don't have a cubital tunnel syndrome or a Guillan's Canal compression.

I make sure that they don't have something else going on. But now I'm much more comfortable saying, I think it's all coming from the C6-7 herniated disc, and I think that there's a very good chance that all of it will go away when we operate at that one level.

So remember that we do stand on the Shoulder of giants who came before us, who taught us.

But you have to question everything. You can't just accept what they tell you.

If you take a look here, there is a sponge at the bottom of the scrub sink.

And I was one time washing my hands in a scrub sink, and one of the people who cleaned the room came out and said, why do surgeons always throw their sponges in that sink when there's a garbage can right here? You should just throw it in the garbage can and instead of in the sink, but all the surgeons always just throw it in the sink. Are the surgeons that lazy? Because then he has to go in and he has to grab that and he has to throw it in the garbage.

The reason we do that is that 20 years ago, we didn't have disposable sponges. We reuse them. So we would come up to the sink, we would hit it with our elbow, we would take the sponge, we would wash our hands, and we would put it in the sink, and then at the end of the day, they would take all of those sponges, they would take it back, they would wash it, they would sterilize it, and they would put it back in the wall so that the next day you could use the sponge again.

The professors and I including, including me, who were taught to do that way, got used to throwing the sponge in the sink. So we would just throw it in the sink without even thinking about it. The new young surgeons would come along and see us doing that and say, oh, we should throw the sponges in the sink. I don't know why we throw it in the sink, we just throw it in the sink because that's what my professor taught me. And so that has propagated generation after generation, despite the fact that it makes no sense.

So we should all stop this kind of

Doing things reflexively just because our professor taught it to us. We have to think for ourselves. We have to learn for ourselves. Everything that our professors taught us, we have to respect, but we have to question. We have to assume that half of what they taught us is incorrect. Half of what they taught us is a lie.