Due to circumstances beyond my control ( namely a laptop that grew legs and walked away in Atlanta last week) this is going to be a short blog.

I want to talk about the Sinus Tarsi because I think it is one of the more interesting landmarks of the foot and ankle.

Here’s a picture showing you the location of the Sinus Tarsi:

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Reach down and touch the ankle bone (Fibula) that sticks out on the outside (Lateral aspect) of your foot. Now slide your finger about an inch forward and down and you will feel your finger slide into a little depression. Congratulations, you just found your Sinus Tarsi (from now on known as ST – I’m getting tired of typing that….)

Before we go any further, I should explain that your ST isn’t really a thing. in fact, it is more of a lack of things than an actual structure itself. The anatomical term “Sinus” means some kind of hole or cavity in the body. The term “Tarsi” means pertaining to the tarsal bones. So the ST is just a gap between bones. Which doesn’t sound impressive, but it is actually a really important part of your foot and ankle.

I think of the Sinus Tarsi as the “Barometer” of the foot. If there is anything going wrong in a person’s foot, a quick check of the ST gives me some valuable clues.

Here is a more complete picture of what the ST looks like:

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As you can sort of see from my very low tech picture labeling, the ST falls between three very important bones of the foot: the Fibula, the Calcaneus and the Talus. These three bones slide and glide over each other in order to provide the movements of the ankle. If something is going to go wrong in the foot or ankle, this joint is going to be on the front lines of the battle. The ST also contains a couple of key blood vessels and some ligaments (Anterior Talofibular and Calcaneofibular) that provide stability to the ankle.

When I am evaluating a patient’s foot, I always check their ST right away. I put my thumb in there and push a little. What I am looking for is any pain or swelling. The ST is the perfect place for any small amount of swelling to hide. Someone’s ankle might not look swollen, but if their ST is filled with fluid, their ankle mechanics will be changed and they will have a feeling of stiffness or pain in their ankle. Everyone’s feet are a little different, so I check for swelling in the ST by comparing the sore ankle to the other side.

The ST is almost always swollen after an ankle sprain. But it can also collect fluid if the patient has a chronic foot or ankle issue. For instance, someone who pronates or supinates ( steps on the inside or the outside of their foot) often causes a bit of damage to the surface of their joints with every step. This damage adds up over time and causes a little bit of swelling to accumulate.

A swollen ST is a warning sign. It tells me that there is something wrong and I need to do a little detective work to find out what it is. That swelling will not go away until the issue is cleared up and the injury is healed.

Do you have swelling in your Sinus Tarsi? If so, you need to address the underlying problem. Did you sprain your ankle recently or do you think there is a problem with your foot alignment? Listen to your ST and get it checked out.

Walk well.

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