What Is Sinus Tarsi Syndrome?

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Sinus tarsi syndrome (STS) is a clinical condition characterized by ongoing pain in the anterior (front) lateral (side aspect) of the ankle—between the ankle and the heel—which is usually a result of traumatic injuries. The most common cause of sinus tarsi syndrome is thought to be a result of chronic or long-term ankle sprains.

According to Podiatry Today, “The sinus tarsi is an anatomical depression on the outside aspect of the foot that is filled with soft tissue structures: ligaments, muscle, nerves, blood vessels, and fat.” The pain resulting from sinus tarsi syndrome may be from injury to the ligaments, and instability of the joint, Podiatry Today goes on to explain.

The condition itself is considered a syndrome; a syndrome is defined as a group of symptoms which occur together, or a condition that is characterized by a group of associated symptoms.
History

The condition was first diagnosed in 1957 by Denis O’Connor, who also suggested a surgical procedure called the O’Connor procedure as the primary treatment for STS. The surgical procedure to correct STS involved removal of part or all the contents of the sinus tarsi—including the soft tissue structures.
Symptoms

Symptoms of sinus tarsi syndrome include:

chronic (long-term) pain along the front and side aspect (also called anterolateral) of the ankle
pain when the foot is turned in (inversion) or turned out (eversion)
a feeling of instability of the foot or ankle (when bearing weight)
difficulty walking on uneven surfaces (such as grass or gravel)
swelling
tenderness of the sinus tarsi area of the foot
ecchymosis (bruising)

Possible Causes

Chronic ankle sprains are mostly due to a weak ligament in the ankle, called the talofibular ligament, according to Physiopedia. Other causes of sinus tarsi syndrome (other than chronic ankle sprains) may include:

cysts
degenerative changes (progressive and often irreversible deterioration; loss of function in the tissues)
injury to the extensor digitorum brevis muscle (a muscle located on the top of the foot)
a severely pronated foot

Note that pronation of the foot is a natural movement that occurs when the foot lands during running or walking. However, when a person overpronates the foot, it can cause pressure on the sinus tarsi. This can result in sinus tarsi syndrome. The treatment for overpronation involves orthotics (special shoes) that can help control the motion of the foot.
Diagnosis

Diagnosis of Sinus Tarsi Syndrome may involve:

X-rays
a bone scan
a CT Scan
an MRI (reveals changes in the soft tissue of the sinus tarsi such as scar tissue from previous injuries)
an injection with a local anesthetic (to help the healthcare provider locate the area of the problem)
an ankle arthroscopy (a narrow tube attached to a fiber-optic video camera, inserted through a very small incision [the size of a buttonhole], to view and diagnose joint problems)
ruling out other problems of the foot

According to Podiatry Today, an MRI is the best method of diagnosing sinus tarsi syndrome, because of its ability to effectively exhibit the soft tissue structure.
Treatment

Conservative (non-invasive) treatment of sinus tarsi syndrome is considered “generally very effective,” according to the American Academy of Podiatric Sports Medicine (AAPSM). Conservative treatment modalities may include:

anti-inflammatory medications
steroid injections
physical therapy
orthopedic shoes to stabilize the area
immobilization of the foot
bracing or taping (to stabilize the area)
over the counter or custom orthoses (the correction of disorders of the limbs by the use of braces and other devices to provide support)

Surgical Treatment

On rare occasion, surgery may be required when conservative treatment measures fail. The surgical procedure may involve open surgery (via a surgical incision) or closed surgery (conducted using arthroscopy).

Surgery should generally be chosen only as a last resort when all other non-invasive treatments have failed (such as immobilization, bracing, and more) says AAPSM.
A Word From Verywell

Sinus tarsi syndrome (STS) is a condition that is common in those who have had an ankle sprain. It’s vital that a correct diagnosis is made for STS because the treatment is significantly different than that of other types of foot injuries. Although conservative treatment is often successful, surgical intervention is required in some instances of STS. Surgery should only be considered as the very last resort for treatment of sinus tarsi syndrome after all non-invasive conservative treatment modalities have been adequately pursued.