Today on the Doc on the Run podcast, we’re talking about how sinus tarsi syndrome can cause flexor hallucis longus tenosynovitis.
This episode has a whole bunch of terms that you may have never heard before. One of them is sinus tarsi syndrome, and the other one is FHL tenosynovitis, or if you really want the long-term it’s flexor hallucis longus tenosynovitis. We’re going to talk about these things.
The first thing is sinus tarsi syndrome. What is that? Well, this is a thing that can happen if you sprain your ankle, if you roll your ankle, there are a few different reasons you can get it, but that’s really one of the most common ones.
When we talk about the sinus tarsi, it’s a part of your foot, where, if you look at the outside of your foot, where you’ve got the little toes over here, the big toe over here, and this is your fibular ankle bone, you have your heel bone back here, and then your talus is sitting on top of there. Your shin bone is up over that and this little hole in there is actually what we call the sinus tarsi.
If you’re trying to look for this on your own foot, it’s actually really not that hard to find. If you want to look for it, I’ll show you how. This is your foot and if you look at the outside of your foot, where the ankle bone is, and you feel this little soft spot right here, right in front of that lump of bone that we call the fibula.
Well, that’s your sinus tarsi and if you get sinus tarsi syndrome, if it gets pinched and irritated when you move your foot, then it starts to hurt. So, why is that? How does this happen? Well, there’s a couple reasons for that. One of them, in the simplest terms, if you think about this. If you look at your foot, if you think about it. Well, basically, when you pronate, and you squish the tissue in the sinus tarsi over here, it irritates the tissue that lines that joint.
One of the simplest ways to not irritate it is to not pronate, not to squish it like that. So if you tilt your foot outward, then you hold it in that position, it stretches that stuff out, the synovial tissue, the painful tissue on the inside of the joint, and it’s not as irritated and it doesn’t hurt as much. Well, how can you do that? Well, one way you can do that is by pulling the big toe and the first metatarsal down against your ground to supinate your foot. So when you pull this one down, it actually supinates and opens this up over here.
What does that mean in terms of this other thing that we’re talking about, which is the FHL or, again, if you want the long-term flexor hallucis. Hallux flex means to pull down. Hallux is the name for the big toe and there’s a long one in a short one, so we’re talking about the long one that attaches to the end of your toe. Then tenosynovitis is the inflammation of the lining of the tube, or the sheath, that goes around the tendon.
When we look at the inside of your foot, this is the outside of your foot over here. This is what we call the lateral view, or the view from the outside and if we look at the other side, where we have the medial view of your foot. You have the metatarsal going out toward the big toe joint here, and then you have two little bones, the proximal phalanx, and the distal phalanx here.
You have the canoe that forms a whole bunch of other stuff. But the flexor hallucis longus tendon comes down, around your ankle, right up over your arch, underneath there, and then goes down the sesamoid bones that are embedded and attaches out here. So, it goes all the way down here. Your plantar fascia, the thing that gets irritated the most, is way down here, but it’s oftentimes confused with planter fasciitis, because it’s in the same neighborhood. But if you get inflammation of the tube that goes around that tendon, you may have arch pain. You may think you have planter fasciitis, but it’s because the lining of this tube, around the tendon, gets inflamed and irritated.
But again, it gets overused sometime, because you’re pulling your big toe down excessively trying to push your foot into supination and tilt it over to hold it there, to take all of the irritation off of the sinus tarsi on the outside of your foot.
If you’re compensating, meaning that you’re walking, limping, walking funny, in order to decrease the stress and strain on that tissue on the outside of your foot, just by pulling down to supinate your foot, then that actually can cause that problem and actually lead to this arch pain on the inside of the foot, which is completely opposite from the first problem. But that’s how that can actually happen.
So, if you find this useful, if you please like it, please subscribe, please share it with somebody else. If you have any questions about foot and ankle problems related to running, you can send them to me at email@example.com and I’ll see you in the next training.