What Is Os Trigonum Syndrome?

An os trigonum is a small extra bone in the back of the ankle. Up to 15 percent of people have this extra bone. It often is found on both ankles.

Os trigonum syndrome results in pain at the back of the ankle due to pinching of this bone or the surrounding tissue. It can occur from repeated minor injuries involving pointing the toes or jumping, downhill running and kicking. Less commonly, it can occur if you are in kneeling with your toes pointed.


A patient can experience pain and stiffness in the back of the ankle and pain when pointing the toes. It also can be associated with pain when moving the big toe because the big toe tendon runs close to the os trigonum at the ankle. Often symptoms are worse when patients are active and improve with rest. 


Patients usually are treated at first with rest, ice, anti-inflammatory medication, and possibly immobilization. Sometimes an injection of numbing or steroid medications may help to relieve the pain as well as confirm that the pain is coming from this area. If pain persists after non-surgical treatments, surgery often will be considered. Surgery involves removal of the bone. It can be done through an open procedure or less invasively, depending on the anatomy.  


Healing without surgery may take several months, but there should be improvement before this. Patients wear a surgical boot for 2-4 weeks. Activities may be resumed as symptoms allow, although the ability to run and play jumping activities such as basketball comfortably may take 3-5 months. Full healing may take up to a year.

Risks and Complications

All surgeries come with possible complications, including the risks associated with anesthesia, infection, damage to nerves and blood vessels, and bleeding or blood clots. Also, there are two main sensory nerves on either side at the back of the ankle which are at slight risk, but the surgical approach generally avoids them.


Did this occur because I broke a bone in my ankle?
No. The os trigonum is a naturally occurring bone in up to 15 percent of people who are walking around with no symptoms in this area. It is joined to the rest of the ankle bone by a thick but slightly flexible cartilage. Some people can develop pain if they damage this attachment. As noted above, this damage can occur either with repetitive small injuries or by one big injury. There can be a broken bone in this same area, but generally it looks quite different on X-ray. 

Does the removal of this bone affect my athletic ability? 
No studies to date show an impact on athletic ability. Most people improve because they no longer have the pain, and most people get back to full athletic activities. It can take several months to get there to allow for slow healing.

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