Can you get a false negative if you’re looking for a fracture with an ultrasound unit? Well, that’s a great question and that’s what we’re talking about today on the Doc On The Run Podcast.
Many times, when I go to see a runner who’s had a sprain or a trip or a fall or something, or maybe even they think you have a stress fracture, but in any event, they’re concerned about a fracture. They think there might be a crack in the bone.
When I see them most of the time, what I do is I actually take a portable ultrasound unit with me so that I can actually look at the foot on the spot and try to figure out whether or not there’s definitely a fracture.
Well, there’s two ways to think about this. When you look at ultrasound units and you’re trying to look at the bone, we know that ultrasound isn’t the best way to image bone, but it actually can show you lots of stuff, particularly if you have a definite crack in the bone where it’s gapped because the ultrasound shows up as a sort of a dark line on the bone that’s white on ultrasound because the ultrasound waves don’t penetrate the bone until it opens up as a crack and then it can penetrate.
Ultrasound can be a really useful tool to try to figure this out on the spot really quickly without any radiation at all. And of course, X-rays, CT scans, those kinds of things actually use radiation to image your bones.
I had a question about this as a comment on one of the Doc On The Run YouTube video episodes where I was talking about ultrasound imaging in the foot when you’re a runner. The question was, “Can you get a false negative? Can you get a false positive?”
Well, these are good questions and the short answer is that when the bone is completely intact, and you have a stress fracture, you get a little bit of a sort of hazy elevation of the covering in the bone with fluid in there that we can see on ultrasound. Now can you get that from other things? Maybe. The more important thing is, can you get a false positive, meaning that we look at with ultrasound and go “Oh, no, your foot’s broken. You have a crack in the bone.” And this episode is about that specifically, and yes, you can.
In fact, I just saw someone recently, who is actually a young girl. She runs, she plays soccer and she actually rolled her ankle and she had a lot of pain. Her pain was right on the fibula bone. The fibula bone is one of the things you can break when you roll your ankle. So, I looked at it with an ultrasound unit and she had instead of just a smooth covering the bone, the smooth layer of the bone in several different ways. I was looking at it with the ultrasound unit, I could see what appeared to be a sort of ripple or irregularity that looks just like a non-displaced fracture where the bones cracked but it isn’t moved apart.
The sound waves don’t go way down into the bone because the bones are together and so it looks irregular. So, what did we do? Well, I got an X-ray and when we got the X-ray we were able to confirm that no, the bone was not broken. So, what is that? Why would you see this false positive, this thing that looks like a fracture, but it’s not?
Well, it’s really simple. She’s young. So, if you’re in this range where the growth plate in the bone where the bone is actually growing has started to close, but it’s not completely developed, remodeled in a way that makes the bone totally smooth, you see the surface irregularity in the bone that’s the growth plate, but it’s not broken. It’s just that it looks like a fracture in some kids.
The chances of getting something like a false positive on an ultrasound is way higher in kids than it is in adults because in adults, there’s less of those irregularities that could look kind of like a crack on an X-ray. So again, you got to really think about these things if you’re an athlete, you have to think about what it means because if you’re going to get back to activity as quickly as possible, you have to be treating the right condition and not over diagnosing yourself with something that is actually going to limit you for a much longer period of time.
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