Can an MRI miss a plantar plate strain? Well, that’s a great question and that’s what we’re talking about today on the Doc On The Run Podcast.
Plantar plate injuries are very common and they are extremely annoying. I get lots of questions and comments both from the podcast and from the Doc On The Run YouTube channel and today’s episode actually comes from a question posted by Jason on the Doc On The Run YouTube channel and he said really simply “Can MRI miss a plantar plate strain?” and the short answer is yes. And I’m going to try to explain why.
There are really two reasons that an MRI might miss a plantar plate strain. The first thing is you have to realize the plantar plate ligament, this is your foot, this is your big toe, that’s your second toe, the plantar plate ligament is a little ligament on the bottom of the joint right here. When you get an MRI of your foot, you have over a hundred images taken during the MRI of the inside of your foot. The problem is, is that many times the slices or the distance between those two views of your foot are three and a half or four millimeters.
The plantar plate is tiny. It’s very thin, it’s very small, and many times you only have half a dozen images or less that actually look at the ligament out of over a hundred images. So, most of the MRI is not looking at the plantar plate ligament at all and if you think about it, if let’s say that my hand is the ligament if you do a slice here, you don’t see it. If you do a slice here you only see the middle of it and if you do a slice up here, you don’t see it at all.
In the next view where they do it side to side, you might have a slice here that misses it, a slice here that misses it and a slice there that misses it, you don’t see it at all. So, there’s a way that you can get an MRI and first of all, it’s not even looking at the entire ligament. It’s just seeing near the ligament and so if you have a small tear in the ligament, you might actually miss it. So, that’s reason number one, the size of the injury versus the size of the MRI image slices might be so small that you just miss it because the slices of the MRI imaging are too big.
The second reason is the main reason it gets missed in runners and that’s chronicity of the injury. What do I mean by that, well, a simple way to think about this is that an MRI actually takes images of your foot based on the amount of water content within the tissue. That’s how you get the different gradations of black and gray and dark gray and white that actually show you the picture you see on an MRI. An MRI is not in color, it’s black and white, but it’s based on the amount of water in the tissue.
So, let’s say you tear your Achilles tendon halfway through. Alright, so you rip half of your Achilles tendon and you have this huge collagen bundle but it’s ripped in half on the side. If you get an MRI right after you have the injury, while you look at it and not only can you see a gap, there’s a bright white line where there’s inflammatory fluid sitting in that gap. If you have a partial split up and down in the perineal tendon, well there’s a bright white line right after it happens because there’s an inflammatory fluid sitting in that space.
But what was interesting in 1998, a guy named Matt Rocket who actually was the director of the one of the surgical residency in Foot and Ankle surgical residency in Harris County, Houston, Texas. Well, he did a very interesting study where they took people that they had suspected had ligament tears around the foot and ankle, and so a ligament and tendon tear. So tendons connect muscles to bone. Ligaments connect bone to bone, and they’re very similar in their structure. That just one connects bone to bone, the other muscle to bone.
In this study, what they did was when people had suspected tears, they took them and they did MRIs and then what they did was they did a diagnostic ultrasound with a musculoskeletal radiologist actually looking at them to see if they could see a tear. And then they did surgery to go in and look at it intra operatively and see is it really torn or not and if it is torn, we’ll go ahead and sew it up and fix it or do whatever we need to do to repair it.
Well, what they found was really interesting. The sensitivity meaning how often it actually saw one of these tears and the MRI was only 23.4%. That is not good. What that means is that you missed more than two thirds of them. This is not good, right? So, you have actually missed 76% of them. So, you missed like three quarters of them. That’s not good. And the overall accuracy meaning that not only it missed them, it actually showed you exactly what was going on was about 65% on the MRI.
Now, ultrasound was way better. So, looking at this with an ultrasound where you can actually stretch it. So, if I see what I do is actually put the ultrasound unit on your foot. I’m looking at the plantar plate, and then I moved the toe to actually distract the toe and do this thing where I stress the ligament to see if it opens up. Now that it opens up, you know for sure you got a tear but ultrasound was 100% sensitive.
Ultrasound, didn’t miss any of them. Whereas MRI missed about 75% of them and one of the things Dr. Rocket talked about in that study was that when you have a chronic injury like a plantar plate sprain that’s been bugging you for weeks or months, well, then what happens is the amount of water content in that area where you have the strain actually goes down. If the water content has decreased in the tissue, it doesn’t show up as a bright line and it gets missed on the MRI.
So Jason, I appreciate you posting your question on the Doc On The Run YouTube channel. Hopefully you guys found this interesting. If you haven’t checked it out, you might want to check out the plantar plate masterclass. It’s free, it’s a deep dive into all these kinds of things and you can get it for free at docontherun.com/plantarplatemasterclass.
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