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Assessing alignment of the lateral cervical spine (neck) X-ray

Video transcript
SAL KHAN: This is Sal here again. And I'm still here with my good friend Dr. Mahadevan from Stanford University. And in the last video, we had looked at adequacy of x-rays, for the neck, which is, is the x-ray good enough. But now let's assume we have good x-rays. Now, what do we look at? DR. MAHADEVAN: The next step is to look at the alignment. So we talk about the ABCs of reading a cervical spine film. And A starts with adequacy, that we went over. And the second part of A is alignment. SAL KHAN: OK. So we're still in A. So now it's alignment. I was expecting something with a B. All right, alignment. All right. So this looks like this is about alignment. DR. MAHADEVAN: This is about alignment. And there's four lines that we look at. The first is the anterior vertebral body line. SAL KHAN: OK, AVBL, right over there. DR. MAHADEVAN: Exactly. And basically, what you're doing is, you're trying to draw a smooth line that connects the anterior aspect, the front of all the vertebral bodies. It should be nice and smooth. It's usually curved. And all the points should sort of fit on that line. Nothing should be off of that line. That would suggest that there was a problem there. SAL KHAN: I see. And anterior, as you just said, means front. DR. MAHADEVAN: Exactly. SAL KHAN: Right, OK. DR. MAHADEVAN: The next line is going to the back of the vertebral body. It's the posterior vertebral body. SAL KHAN: So not the back of the entire vertebrae, the vertebral body, which is this boxy part right in front. DR. MAHADEVAN: Exactly. And so same thing, connecting a line up and down should be nice and smooth, as you've drawn it. And nothing should fall off that line. No piece of that vertebral body should fall off of the line you've draw. SAL KHAN: All right, sounds good. And then? DR. MAHADEVAN: The next is, we connect all the spinolaminar junctions. So this is the spinolaminar line. And it's where the lamina connects to the spinous process. SAL KHAN: Spinous process, it sounds like we could make a whole video about that. DR. MAHADEVAN: Spinous process, if you look at the back of somebody's neck, are those little bumps that you can see. And that's the very back end. SAL KHAN: And that's these triangular things right here. DR. MAHADEVAN: Exactly. SAL KHAN: OK. So you're just connecting that line. Kind of the front of these triangles, the base of these triangles, so to speak. DR. MAHADEVAN: Exactly. SAL KHAN: And then the last one? DR. MAHADEVAN: And the last line is the spinous process tips. And again, we're just connecting the top, the tip of all these spinous processes, the little bony projections you can see if you look at the back of somebody's neck. And these two should generally fall in a nice, smooth curve. SAL KHAN: And so the general rule-- if any of these aren't aligned the way that we've drawn here, it's a problem. DR. MAHADEVAN: Exactly, exactly. We call it subluxation or malalignment or misalignment. And these all suggest that there is a problem there. SAL KHAN: Which is a big deal, because your spinal cord is running through there. DR. MAHADEVAN: Absolutely. If you look between the two, the green and the blue line, that's actually where your actual spinal cord runs. SAL KHAN: Right. Right down there. DR. MAHADEVAN: Exactly. SAL KHAN: I see. So you don't want that to get messed up. All right. So let's look at a few of these x-rays and see if, one, anything's wrong. Or if there's something, if we can spot it. DR. MAHADEVAN: Actually, Sal, now that you know how to read cervical spine x-rays. I'm going to have you look at the first x-ray. SAL KHAN: OK, let's see. I'm going to get sued for malpractice. Let's see. All right. So this one over here. So let me just do the first one. Let me just go with what you told me to do. So I'm going to do the anterior side of this vertebral body. DR. MAHADEVAN: Exactly. SAL KHAN: Look, I'm learning the words too, talking like a doctor. So I'm going to draw a line here. That looks pretty good. That looks decent. What is it? I'm kind of-- let me see. This still looks decent. And that doesn't look great. Would this count? I mean, this looks like it got shifted over a little bit. DR. MAHADEVAN: Absolutely. SAL KHAN: It's not a huge shifting. But it's enough that it's not easy to draw a line. So I was right? DR. MAHADEVAN: You're absolutely right. And in fact, sometimes it's very subtle. And you picked up a very subtle abnormality. But again, even though it's subtle on the x-ray, it could be serious for the patient. So you potentially saved their spinal cord and their lives, by picking up an injury like this. SAL KHAN: OK, good. You're making me feel-- very good. So that's-- it's literally something as subtle as that is what you're looking for. DR. MAHADEVAN: Exactly. Again, it should be a nice, smooth line or a nice, smooth curve. And as you can see, at that junction, it's no longer smooth. SAL KHAN: And you don't even have to look at the other lines. Any one of these that you don't align, that's enough to say, hey, do something else. DR. MAHADEVAN: Exactly. And that's a great, important teaching point, which is, if you see any abnormality on a plane film on an x-ray like this, you stop. And you protect their cervical spine. And then you get a more important study or a better quality study, like a CT scan. SAL KHAN: Fascinating. Although if I do look here, it does look like we could have done the PVBL. And it looks like that also is a little off too. DR. MAHADEVAN: Absolutely. SAL KHAN: That one and-- OK, well, let's get a few more. DR. MAHADEVAN: Great. SAL KHAN: I don't want to focus too much on my first victory. All right. So it's clear this person is facing this way. I can see their teeth. So let's see what we can do here. Can I give it a shot again? DR. MAHADEVAN: Please, please. SAL KHAN: So let's-- the AVBL, it looks pretty good. This is-- well, that looks close. DR. MAHADEVAN: It looks close, I agree. And potentially, again, you've got a very keen eye and might have picked it up. But most people might-- SAL KHAN: A gift, you might say. DR. MAHADEVAN: --might have overlooked that. SAL KHAN: So let's try the other lines here. OK. So this one is more obvious. This one is more obvious that there's kind of that disconnection right over there. DR. MAHADEVAN: Exactly. And this is the PVBL, or the posterior vertebral body line. You can see clearly, that line is not smooth. It doesn't connect, and so there is a problem right there at that junction. SAL KHAN: OK. All right, and so now we have this last one right over here. Let me see what I can do. Let me see, don't want to lose my streak. All right. So interior side-- this actually looks pretty perfect actually. DR. MAHADEVAN: And in fact, it is a perfect. SAL KHAN: OK. Let me try the next lines here. This is the posterior vertebral body. Let me do that in a color that's easier to see. I already used orange. I'll do magenta. All right. So this is looking OK. It looks OK. I mean, nothing obvious on that line. DR. MAHADEVAN: I would say, again, you've got the keen eye. But in this particular case, I'd say, it's fine. It's within the normal range, as we say. SAL KHAN: And so let me do the base of those triangles. Let me do-- so this is a triangle right over here. DR. MAHADEVAN: Again, you want it to be a nice, smooth curve. Everything should fall on that curve. SAL KHAN: So this-- I would have to be a little bit generous with my curve to make it go to these guys down here. DR. MAHADEVAN: Exactly. And this is the spinal laminar line. This is the third line of alignment. As you can see, to try to get those to work, you could. But they're not smooth like the other lines. And this is, again, another subtle finding. But missing this finding because the first two lines are normal could again be devastating for the patient. SAL KHAN: Right. You always want to err on the side of caution. I mean, if anything looks even a little bit suspicious, maybe another x-ray. DR. MAHADEVAN: Yeah, another x-ray, another view, like we talked about before. Or the definitive study is a CT scan, or Computed Tomography. SAL KHAN: I see, very cool. Well, thanks for this. This is useful. DR. MAHADEVAN: My pleasure.