Sinus tarsi

What it means

The sinus tarsi is a small, funnel-shaped space located on the outer side of the foot, just in front of the ankle bone, where the talus (ankle bone) and calcaneus (heel bone) meet. Rather than being empty, it is filled with several small ligaments, fatty tissue, blood vessels, and a rich supply of nerve endings that help the brain sense the position and movement of the foot and ankle, a function called proprioception. This makes the sinus tarsi important not just structurally, connecting the talus and calcaneus, but also for balance and coordinated movement.

Why it appears on a CT or MRI report

Radiologists mention the sinus tarsi when describing this region of the foot, whether it appears normal or shows a change such as fluid, scarring, or loss of the normal fat that fills the space. MRI is particularly useful here because it can show the small ligaments within the sinus tarsi and detect inflammation or fluid replacing the normal fatty tissue, a pattern often linked to injury or chronic irritation. CT and X-ray are more useful for evaluating the bones on either side of the space and any related fracture.

What it usually means

On its own, naming the sinus tarsi simply identifies this small anatomical space and does not indicate a problem. When changes are described, such as fluid or scarring within the sinus tarsi, this is often associated with sinus tarsi syndrome, a condition causing pain on the outer side of the ankle and foot, frequently following an ankle sprain or from repetitive strain. It is thought to relate to inflammation, small ligament injury, or scar tissue within this crowded space, sometimes alongside chronic ankle instability. Most cases improve with conservative measures, including rest, bracing, physical therapy focused on ankle stability, and occasionally a corticosteroid injection into the sinus tarsi itself to settle inflammation. Persistent or severe cases are less common and may prompt a more detailed specialist evaluation.

When to follow up

The term itself does not require action; what matters is how it is described together with your symptoms. See a doctor if you have persistent pain on the outer side of your ankle or foot, particularly after a sprain or with a sense of ankle instability, or if the pain does not settle with rest and simple measures. A clinician can examine the foot, correlate any imaging findings, and guide treatment such as bracing, physical therapy, or an injection if appropriate.

A plain-language way to picture it

Picture a small, cone-shaped pocket tucked between two bones on the outer side of your foot, packed with tiny ligaments and padding, a bit like the stuffing inside a small cushion wedged between two joints. That padding helps cushion and stabilize the area and feed your brain information about where your foot is in space, but if it becomes inflamed or scarred after an injury, that snug little pocket can become a persistent source of ache on the outer foot.