#378 What are sesamoid bones in the foot - DOC

#378 What are sesamoid bones in the foot

Today on the Doc On The Run Podcast, we’re talking about we’re talking about the sesamoid bones in your foot.

What are the sesamoid bones in the foot?

This is a great question sent in by a runner who got an injury, and the doctor pointed out these things called the sesamoid bones on the X-ray, but this runner still wasn’t sure what exactly that meant. 

So I thought it was a great thing to talk about because they are very prominent. And interestingly, when I have seen patients, I’ve done X-rays on their foot, whether it’s for addressing a bunion deformity, or they have a metatarsal stress fracture, or some other condition, it is interesting to me that how frequently runners see these two lumps on their X-ray near the big toe joint and they think that it’s a tumor or some kind of problem. But it’s not a problem. They’re just the sesamoid bones. Everyone has them. They are normal.

Sesamoid bones are types of bones that are both in and out of a joint. And what that means is that it’s half of the bone is actually inside the joint, or what we call intra-articular, meaning within the articular or joint surface. And then it’s also partially extra-articular, where part of the bone is actually not in the joint and bathed in the fluid inside the joint at all. And they’re always embedded within a tendon of some type.

The largest sesamoid bone in your body and the one you’re probably most familiar with is the patella, or your kneecap. And so the patellar tendon is the one that actually holds the kneecap in place at the front of your knee. But when doctors talk to you specifically about the sesamoid bones, we are referring specifically to the two sesamoid bones under the big toe joint. Now the sesamoid bones are embedded within this tendon called the flexor hallucis longus tendon. And that is the tendon that actually pulls your big toe down against the ground when you stand or walk or run.

As your heel bone starts to come up off the ground as you run or as you walk, the metatarsal bone actually is on top of the sesamoids and that metatarsal bone starts to rotate over the sesamoid bones, pushing them tighter and tighter between that bone and the ground as that flexor hallucis longus tendon actually starts to tighten up. So when your heel comes up off the ground, when you stand up on your toes, when you’re doing push-ups and bending the toes, you’re actually pressing the sesamoid bone up against the bottom of the first metatarsal bone with a lot of force.

And so that’s what the sesamoid bones are. They’re two little bones. They’re about the size of kidney beans. They sit under your big toe joint, under the first metatarsal bone, specifically the head of the first metatarsal bone, right at the ball of your big toe joint. 

When you have pain under the big toe joint, it can be worrisome if you’re a runner, because it could be something like sesamoiditis or even a sesamoid stress fracture. But you do have two of them, so you have to figure out which one it is and you have to figure out how bad it is. So it could be a stress response. It could be a stress reaction. Could be a stress fracture. Or it could be sesamoiditis, where you have irritation, not really of the bone, but the cartilage on top of the bone where the metatarsal sits. But the sesamoid bones are just two little bones sitting under the big toe joint that you can easily see on an X-ray.

And that is what the sesamoid bones are in your foot.

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