What is plastic deformation of a metatarsal stress fracture in a runner? Well, that is what we’re talking about today on the Doc On The Run Podcast.
Metatarsal stress fractures are something I talk about a lot because they’re extremely common and they are one of the most common reasons a runner has to stop running. One of the reasons you would stop running is that you do not want a thing called plastic deformation of the metatarsal.
So, what is that? Well, deformation means that it changes, it warps, it changes and moves out of position. Plastic means it happens gradually over time. It happens as a consequence of a bone callus stretching. So, let’s talk about how that happens.
When you look at a foot model or you look at your x-ray from the side view that looks like this, so I’m sure if you got a stress fracture you had an x-ray that was called the lateral projection that looks sort of like this view. When you look at it, we can look at the metatarsals on that x-ray and we see like, are they lined up or not? So, if one of them is out of position, that is bad.
They’re supposed to be all lined up because when you stand on your foot, you want the forces distributed evenly across the heads of the metatarsals where they contract the ground so that when you push off, forces are applied evenly through those metatarsals. Roughly speaking, when you run, you have about half of your body weight going through the first metatarsal and as you can see, it’s huge compared to the others and then the other ones divide up the rest.
If this is 50% and these are all 50%, that means these are only about 12.5% each. So, if they’re 12.5% each and one of them moves out of the way and is no longer contacting the ground, that means that each of these then has a significantly higher portion of stress applied to it. So, what happens when you get a stress fracture is, let’s say it’s the second metatarsal, you get a crack down on the bottom down here. If you get a crack and you think, well, it doesn’t hurt that bad. It’s not really that swollen. I can still put my shoe on. It’s a little black and blue, but who cares? I’m going to go for a run today.
It aches a little bit, but it’s not killing you. You kind of forget about it in the evening. It’s not that bad, but again, you’re a runner with a high pain threshold and you figure, I can tolerate this. I got a marathon in a month. I’m just going to keep training. I’m going to do this. I’m going to do my event. I put in all this work. I’m not skipping it and you don’t get it checked out and you don’t really take action to try to remove any stress or strain from that metatarsal. It gets worse.
Then eventually it cracks and then what happens is that if it’s in the right position still, when it cracks, where the crack in the bone is, it gets a blood clot. That blood clot turns into a soft callus that is basically like kind of plasticky and so you have this little clot that forms like glue. It gets some collagen fibers in it. It gets sort of gummy and sticky, and then it starts to turn solid, but it is still soft.
Before it calcifies and turns into solid white bone that you would see on an x-ray, if you’re running on it and you’re stressing it and you’re pushing on it, then it can actually tilt upward. And then if you looked at that side view x-ray, where it looks like this, then one metatarsal may be elevated. That happens gradually as you stretch the bone callus, it pushes it up and changes its position. That is very bad because now you’re at much higher risk for getting stress fractures on the other metatarsals.
Believe it or not, I saw a guy one time that had a third metatarsal stress fracture. He completely ignored it. It completely cracked, moved out of position. Then it healed in that position and then later he got, guess what? All those forces went sideways. So, he had a fourth metatarsal stress fracture. And then after that, not making this up, he had a fifth metatarsal stress fracture because those forces that were no longer being absorbed by the third metatarsal got moved over to the fourth and then to the fifth as a consequence of this plastic deformation.
You do not want to move the bone out of position when you break it. If it’s cracked and it’s just a stress fracture that is non-displaced and it’s in the right place, you want to leave it there. Do not ignore the discomfort you have when you have a stress fracture.
If you want to learn more about stress fractures, you can come check out a presentation I put together. You can get it for free at www.stressfracturesecrets.com. So, come check it out and I’ll see you in the training.
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