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What Is Os Trigonum Syndrome?

Os Trigonum

The os trigonum is a bony ossicle, or a small bone, developed at the back of the ankle talus bone. Formed during the ages 7 to 13 years old, this happens when a part of the bone is not fully fused with the talus, causing an extra bone to jut out from behind.

Os Trigonum Syndrome

Patients with os trigonum syndrome may or may not realize the condition. Some people feel pain at the back of the ankle early on while others may only feel the pain when triggered by an injury. This syndrome is commonly experienced by ballet dancers, soccer players and people who are highly active in sports that require frequent downward pointing of the toes. Known as the “nutcracker phenomenon”, the injury occurs when the toes are pointed and the os trigonum is crushed between the talus and heel bones, causing the surrounding tissue to be torn and inflamed.

This condition has many names. It could also be called posterior tibial talar impingement syndrome, symptomatic os trigonum or the talar compression syndrome.


Os trigonum syndrome causes one to experience a deep aching pain at the posterior of the ankle, especially when toes are pointed downward or pushing the foot off the ground. The injured area also feels tender with visible swelling and reduced plantarflexion.


To diagnose the condition, the doctor will ask questions about activities that the patient is involved in and the development of the symptoms. The MRI is the preferred scan as it can show the size of the os trigonum and the extent of the damage. However, an X-ray, MRI or CT scan may also be ordered.


Non-Surgical Treatment:

Conservative treatment is usually recommended as the first approach to treating os trigonum syndrome as it yields a high success recovery rate.

Patient first has to completely stop all activities that can aggravate the injury for about 4 to 6 weeks to allow the inflammation to subside. Icing the area would help reduce the swelling. The foot is then immobilized in a boot or cast to reduce weight bearing. Oral medication and injections may be prescribed to relieve the pain, followed by regular sessions of physical therapy.

Surgical Treatment:

If the condition does not improve with non-surgical treatment, surgery would be considered provided that there is no infection in the skin and soft tissue around the area. Endoscopic os trigonum resection is a commonly used method as it helps the foot regain mobility and relieve other symptoms with less scarring and faster recovery.

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