Sinus Tarsi Syndrome: Causes, Symptoms, and Assessment

Pain on the outside of the ankle can be frustrating, especially when it does not feel like a simple ankle sprain. You may notice discomfort when walking on uneven ground, running, hiking, cutting, balancing on one leg, or standing for long periods. In some cases, the ankle may feel unstable, irritated, or difficult to trust.

One possible cause of this type of pain is sinus tarsi syndrome.

Sinus tarsi syndrome is a condition involving irritation of a small space on the outside of the foot and ankle called the sinus tarsi. This area sits between the talus and calcaneus, two important bones that help form the subtalar joint. The subtalar joint plays a major role in how the foot adapts to the ground, especially during walking, running, and uneven-surface activity.

When the tissues inside this space become irritated, overloaded, or sensitive, it can create pain deep in the outside part of the ankle.

What Is the Sinus Tarsi?

The sinus tarsi is a small tunnel-like space located on the outside of the ankle, just in front of the outer ankle bone. It contains ligaments, blood vessels, nerve endings, and connective tissue that help support and sense motion around the subtalar joint.

The subtalar joint allows the foot to move into pronation and supination. These motions help the foot absorb load, adapt to uneven surfaces, and create a stable base for pushing off.

When this area is irritated, normal movement may start to feel painful or threatening. This can lead to tenderness, stiffness, guarding, and a feeling that the ankle is not as stable as it should be.

Common Symptoms of Sinus Tarsi Syndrome

Sinus tarsi syndrome usually causes pain on the outside of the ankle or outer rearfoot. Symptoms may include:

• Pain just in front of the outside ankle bone
• Pain that feels deep in the outer ankle
• Tenderness when pressing into the sinus tarsi area
• Discomfort when walking on uneven ground
• Pain with running, hiking, or lateral movement
• A feeling of instability or “giving way”
• Increased symptoms after an ankle sprain
• Pain with single-leg balance or cutting movements
• Stiffness or sensitivity during foot and ankle motion

Many people describe the pain as hard to pinpoint. It may not feel like the sharp pain of a fresh ankle sprain, but more like a deep ache, pressure, or irritation that shows up with loading.

What Causes Sinus Tarsi Syndrome?

Sinus tarsi syndrome often develops after an ankle sprain, especially an inversion sprain where the foot rolls inward and stresses the outside of the ankle.

Even after the initial sprain improves, the ankle may not be fully restored. Swelling may go down and basic walking may feel better, but balance, strength, coordination, and confidence can remain limited.

Other contributing factors may include:

• Repeated ankle sprains
• Limited foot and ankle strength
• Poor single-leg balance
• Subtalar joint irritation
• Excessive or poorly controlled pronation
• High training loads or rapid increases in activity
• Running or hiking on uneven surfaces
• Hypermobility or instability in the foot and ankle
• Weakness in the calf, peroneal muscles, hip, or foot muscles
• Stiffness in the midfoot, ankle, or big toe

It is important to understand that sinus tarsi syndrome is rarely just a “spot problem.” The painful area matters, but the bigger question is usually: why is this area being overloaded?

That is why a complete evaluation should look beyond the painful spot and assess how the foot, ankle, hip, and whole lower body are managing load.

Sinus Tarsi Syndrome After an Ankle Sprain

One of the most common stories we hear is:

“I sprained my ankle months ago, and it got better, but it never felt completely normal.”

After an ankle sprain, people often regain basic walking before they restore strength, control, and confidence. The ankle may feel mostly healed, but it may still struggle with running, hiking, uneven ground, or lateral movement.

This can leave the outer ankle vulnerable when activity increases. The sinus tarsi may then become irritated because the ankle is being asked to do more than it is prepared for.

How Is Sinus Tarsi Syndrome Assessed?

Assessment usually starts with a detailed history and physical exam. The goal is to understand not only where the pain is, but also what is contributing to it.

A complete evaluation may include:

• Palpation of the sinus tarsi region
• Assessment of ankle and subtalar joint motion
• Single-leg balance testing
• Foot posture and loading assessment
• Calf strength testing
• Peroneal tendon strength testing
• Hip stability testing
• Gait or running mechanics review
• Screening for previous ankle sprain patterns

In some cases, imaging may be helpful, especially when symptoms are persistent, traumatic, or unclear. X-rays, ultrasound, or MRI may be used to rule out other issues such as fracture, tendon injury, ligament damage, arthritis, or other joint pathology.

However, imaging does not always tell the full story. A painful ankle often needs to be understood in the context of movement, strength, balance, load tolerance, and the person’s activity goals.

When to Get Evaluated

You should consider getting evaluated if:

• Pain has lasted more than a few weeks
• You feel unstable or unsure on the ankle
• You have had repeated ankle sprains
• Walking on uneven ground is painful
• Running, hiking, or sport keeps flaring symptoms
• Pain is limiting your ability to train or stay active
• You are unsure whether symptoms are coming from the joint, tendons, ligaments, or another structure

A thorough assessment can help identify whether the sinus tarsi is involved and what factors are contributing to the problem.

The Big Picture

Sinus tarsi syndrome is often a sign that the outside of the ankle and subtalar joint are not tolerating load well.

The painful area matters, but long-term improvement usually requires understanding the whole system: the foot, ankle, calf, hip, balance, previous injury history, and the demands of the activities you want to return to.

Your ankle is not fragile. It may just need a clearer diagnosis, better support, and a plan that helps it adapt.