What is os trigonum syndrome?
Os trigonum syndrome is a congenital condition that describes pain in the back of your ankle due to an extra bone (os trigonum) behind your ankle bone.
What causes os trigonum syndrome?
Os trigonum syndrome occurs when a person has the extra bone and injures the attachment, such as a sprained ankle. It often results from repetitive stress on your ankle, such as:
- Frequently pointing the toes down, like a dancer
- Kicking a ball repeatedly over time, like a football or soccer player
- Pushing off the back of the ankle, like a runner
What are the symptoms of os trigonum syndrome?
Most people with an os trigonum don't realize they have it until after it's been triggered. If you develop os trigonum syndrome, you'll have symptoms in the back of the ankle, including:
- Pain, especially when pointing your toes down or pushing off the big toe
- Reduced range of motion
- Stiffness
- Swelling
- Tenderness to the touch
How is os trigonum syndrome diagnosed?
If your doctor suspects os trigonum syndrome, they will perform a physical exam and discuss your symptoms and activities. In many cases, an x-ray will be used to provide full visibility of the bones and joints, however, MRI scans are often used to provide additional details on the condition as needed.
What are treatment options for os trigonum syndrome?
Treatment for os trigonum syndrome typically involves resting and refraining from strenuous activity, avoiding or limiting certain movement patterns that may cause pain, immobilization using a boot or orthopaedic device, ice to further reduce swelling, over-the-counter medications like ibuprofen to treat pain, and in some cases, ultrasound-guided injections of corticosteroids (anti-inflammatories) into the back of the ankle to provide pain relief while increasing the patient’s range of motion.
In more severe cases, surgery to remove the os trigonum and surrounding tissue may be recommended. Recovery from this procedure typically takes one or two months, and athletes often return to full activity levels within six months.
Last Medically Reviewed on April 29, 2026.