The Center for Podiatric Care and Sports Medicine

Syndrome of the Day: Os Trigonum Syndrome

Posted by on Friday, July 20th, 2012


The foot has so many bones; in fact, about 25% of the bones in your body are found in your feet. So then why on earth would your foot create extra bones? It is indeed a mystery, but it happens–and it can cause trouble.

Ladies and gentlemen, I give you the os trigonum!

What is the os trigonum? It sounds like the name of a lively Norwegian chef who hosts an adventure-cooking show. Unfortunately, it’s not, though hopefully some network will take that idea and run with it. The os trigonum is a small bone connected to the talus, or ankle bone, by a band of fibrous tissue. It develops when the small bone does not fuse with the rest of the bone in the area during the period when the growth plates are solidifying. In other words, the occurence of an os trigonum is another of the many wonders of adolescence. However, there’s no way to tell if your well-traveled, happy baby will develop it, and probably no need to worry about it; only about 5-15% of the population has an os trigonum.

What does the os trigonum do? Nothing.

What was that? Nothing. It’s just there.

So why should anyone care? In most cases, no one should care. However, sometimes that little useless bone can get itself in trouble.

Should I ask how? Yes, if you don’t mind.

How? Sometimes the bone can get caught between the ankle and heel bones. As the os trigonum is irritated, it becomes inflamed.

I become inflamed when I am irritated. Indeed.

How does the os trigonum get into this kind of trouble? Another injury, such as an ankle sprain, can irritate the os trigonum. It also can be a repetitive use injury for people who repeatedly point their toes down, such as ballet dancers and some athletes. When you repeatedly stand on your toes–picture a ballet dancer doing releves over and over–the os trigonum can get caught between the heel and ankle bones, leading to an impingement there. In fact, the injury is also known as “posterior ankle impingement” (we’ve also covered “anterior ankle impingement”).

What are the odds of that? A person who is one of the only 5-15% of the population who has an os trigonum also gets into a profession that requires the constant irritation of an os trigonum? The odds must be great. Nevertheless, it’s always good to stay on top of these things.

So how would I know if I have it? You would feel intense pain in the back of your ankle when you stand on your toes. There might be swelling there as well, and it will feel sore if you touch it. the best way to find out, though is to see a podiatrist at The Center for Podiatric Care and Sports Medicine (212.996.1900).

Then what would we do about it? In most cases, os trigonum syndrome is treated non-surgically. Start with rest and immobilization, such as keeping the foot in a walking boot. Icing and anti-inflammatories will help bring down the inflammation; sometimes a podiatrist may recommend a cortisone shot to get the pain and inflammation down quickly.

If non-surgical methods don’t help, or if the injury keeps recurring, a podiatrist may suggest surgery to remove the os trigonum. After all, it doesn’t do anything.

Os trigonum syndrome is certainly not a common injury but it can be a huge annoyance if you happen to need to do the things that set it in motion. Watch out, dancers!



If you have any foot problems or pain, contact The Center for Podiatric Care and Sports MedicineDr. Josef J. GeldwertDr. Katherine Lai, Dr. Ryan Minara and Dr. Mariola Rivera have helped thousands of people get back on their feet. Unfortunately, we cannot give diagnoses or treatment advice online. Please make an appointment to see us if you live in the NY metropolitan area or seek out a podiatrist in your area.