The sinus tarsi is a small, bony channel located on the outside of the foot between the ankle and heel bone. Sinus tarsi syndrome is when increased pressure in this area, or problems with the ankle joint, results in inflammation, pain, and instability in the foot.

Sinus tarsi syndrome frequently occurs in athletes and people who experience a sprain due to the ankle rolling outward. Symptoms typically include pain and instability in the foot and ankle. Treatment may include nonsurgical and surgical methods to correct the issue. Once treated, a person can typically resume normal activities.

In this article, we will discuss what sinus tarsi syndrome is, as well as its possible causes, symptoms, and more.

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Sinus tarsi syndrome occurs when swelling and pain occur on the outside of the foot, below the ankle joint, in an area known as the eye of the foot. The joint in the area, known as the subtalar joint, is responsible for allowing rotation of the foot. Some healthcare professionals may also refer to the sinus tarsi as the tarsal sinus.

Dr. Dennis O’Connor first described sinus tarsi syndrome in 1957 after noting pain in the hindfoot that worsened after applying pressure to the sinus tarsi. The condition often occurs due to physical trauma or a series of ankle sprains that cause damage to the local ligaments, which may result in pain and instability of the foot.

A person may develop sinus tarsi syndrome due to several potential causes.

Some experts estimate that roughly 70–80% of cases of sinus tarsi syndrome are the result of ankle sprains, or the ankle rolling outward. The remaining 20–30% occur due to excessive foot pronation, or rolling inward, and may occur over time.

Other sources note that sinus tarsi syndrome commonly occurs due to flat feet. This condition causes either no arch in the foot or one that is very low, which puts pressure on the subtalar joint. This can put extra pressure on the soft tissue in the ankle area, which can result in inflammation of the joint lining or the tissue outside the joint.

Other possible causes may include:

Sinus tarsi typically causes symptoms that include:

Pain typically occurs on the outside of the foot in the back below the ankle joint. Weight-bearing activities, including walking on the joint, can cause a worsening of symptoms.

A person may also notice increased pain when turning the foot inward or outward. The pain may occur when sitting, standing, or walking. When sinus tarsi syndrome occurs, a person may have trouble walking on uneven ground, such as grass or gravel. They may feel unstable when walking or as if their foot may give out on them.

A person will need to contact a healthcare professional, such as a doctor specializing in orthopedics, for a diagnosis. This will typically involve a combination of reviewing a person’s symptoms and when they started. A doctor will also examine the person’s foot. They may check:

  • ability to move the foot
  • for tenderness
  • ability to put weight on the foot
  • presence and location of swelling
  • instability when standing or moving

A doctor will also likely order an X-ray, CT scan, or MRI to examine the foot. Imaging tests can help confirm the diagnosis and rule out other possible causes of the pain and swelling.

Treatments may be conservative or more intensive. In most cases, conservative treatments can effectively help relieve symptoms and treat the condition.

Conservative treatments often consist of:

  • an ankle sleeve
  • taking anti-inflammatories such as over-the-counter (OTC) nonsteroidal anti-inflammatory drugs
  • immobilization
  • wearing stabilizing shoes
  • using OTC orthoses (shoe inserts)

Less conservative treatment options may include:

In some cases, a doctor may recommend surgical intervention. Surgical options may include:

Once treated, sinus tarsi syndrome should fully resolve. The intensiveness of the treatment can influence recovery time.

People who undergo surgery will often need several weeks to fully recover. In some cases, it may take up to 3 months to return to sporting activities and between 6–12 months to make a full recovery. During recovery, a person will likely need to immobilize the ankle and use assistive devices for walking and movement.

It is possible for a person to reinjure the joint. A person can reduce their risk of reinjury through:

  • avoiding uneven terrain when walking
  • not participating in sports or activities that require rapid and sudden changes in direction
  • correcting flat feet with orthotics or surgery

A person should discuss their recovery with a doctor or physical therapist. They can provide guidelines that include how long recovery will likely take and when the person can likely resume certain activities.

Sinus tarsi syndrome refers to pain and swelling on the outer side of the foot under the ankle joint. The condition often occurs due to ankle sprains, overuse, or flat feet. A doctor can often diagnose the condition through a physical examination and imaging tests. The tests can help confirm the diagnosis and rule out other causes of the pain and swelling.

Treatment can vary from conservative treatments, such as OTC medications and supports, to more intensive treatment options, such as steroids and surgery. With treatment, the condition should resolve, and a person should be able to return to normal activities. However, they may want to avoid certain sports that require sudden changes in direction.