What is metatarsal stress fracture troughing? MRI report explained.
I got a call from a runner who had a stress fracture that was not healing, so he did the right thing, and he sought a second opinion. Well, when we were on the webcam call, one of the things that he did not understand was one of the findings on his MRI report that said that he had troughing of the fractured metatarsal bone. And since he had already had an MRI of his foot, in this episode I just thought that it might be helpful since he did not understand it that I could explain to you what troughing really means and how it shows up on an MRI.
It is really simple. What we are talking about here is we are talking about the metatarsals, right? That’s these little bones. Usually, it’s the second or the fourth metatarsal, but you could get a stress fracture theoretically in any of them. And when you get a crack in the bone, it’s usually, the stress fracture is usually in the cortex. Either the middle of the bone, that would be the central cortex, or the distal diaphysis that’s out here next to the lump of metatarsal bone that we call the head of the metatarsal, or it could be near the base and that would be a proximal diaphysis stress fracture.
What is troughing? Well, troughing is simple. Let me see if I can explain it. What I did was I took a piece of PVC pipe to illustrate. A cortical bone is a tubular bone. It really is tubular like this. It’s not perfectly round like a pipe, but kind of like a pipe in that it is round. The cortex is the outer shell, just like this pipe on the insides of the medullary canal. It has soft stuff in it. That’s the bone marrow. It’s mostly fat. It’s very soft and has all the blood supply. That’s where you start getting the inflammation on the inside of it that sometimes shows up on an MRI. But in his case, the bone had broken.
It wasn’t just that there was inflammation. It was broken and he had this thing called troughing and he wanted to know why it was a problem. Well, the first thing is that if you take the bone, and to make this simple, I took the pipe and I cut it in half. Now, you have two, it looks like two troughs, right? Two little troughs. They are sitting there and when you get troughing, they sit inside each other like that. So, troughing just means that the pieces of bone that look like troughs sit in one another and they drop off.
So, instead of being up here, the bone drops off and it gets thinner in one dimension because it’s now thinner this way, but it’s wider that way. Why is that a problem? Well, you want the bone to heal edge to edge or side to side and when it’s troughing, it can’t. So, when it drops down in there, it may delay your healing. That’s one of the problems. Now, you can still get it to heal potentially, but it’s not in the right position and so troughing, what happens is it just sits there, it cracks, and then it slides down into the inside of the bone.
It’s more likely to start getting fibrous material or a bunch of collagen or scar tissue or whatever between those little surfaces, those undulations where it’s sitting in a trough because it doesn’t usually heal straight together very easily that way. It can sometimes heal, but it can often lead to what we call a non-union. That’s why we worry about it. So, troughing is just mean that it is the two pieces of bone are sitting down in the trough. That’s all it is.
If you want to know more about stress fractures, how they actually become a problem, and more importantly for you, the strategies I use with runners who have a stress fracture and want to continue to run or get back to running faster, the same stuff I teach to doctors at medical conferences, you can get it for free in the Stress Fracture Masterclass. It’s a deep dive into those topics specifically. You can get it for free at www.docontherun.com/stressfracturemasterclass. So, come sign up and I’ll see you in the training.
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