OS Trigonum

What is Os trigonum syndrome?

Os trigonum syndrome describes pain that develops in the back of your ankle. This pain is due to an extra bone behind your ankle bone. The extra bone is the os trigonum, so the condition is often called os trigonum syndrome. It’s also called:

• Posterior ankle impingement syndrome.
• Hindfoot impingement syndrome.
• Nutcracker-type impingement (because the os trigonum gets compressed when you point your toes down).
• Posterior tibiotalar impingement syndrome.
• Talar compression syndrome.

Causes

Os trigonum syndrome happens when a person has an extra bone and injures the attachment, such as a sprained ankle. And 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 soccer player.
• Pushing off the back of the ankle, like a runner.

With injury or overuse, the extra bone gets pinched or pulled away from its point of attachment. This can stretch and tear the surrounding tissue, causing irritation, inflammation (swelling), and symptoms.

Symptoms

Most people with an os trigonum don’t know they have it because it doesn’t cause problems.

But if you develop os trigonum syndrome, you’ll have symptoms in the back of the ankle, including:

• Pain, especially when pushing off your big toe or pointing your toes down.
• Reduced range of motion (less ability to fully move your foot).
• Stiffness.
• Swelling.
• Tenderness to the touch.

Some people with this condition adjust how they walk, run, kick or dance to avoid pain. They may do this on purpose or subconsciously.

But changing the foot’s natural position may cause discomfort or pain in other areas of the body. For example, a ballerina with os trigonum syndrome may rotate the foot inward or outward when elevating onto the toes. But over time, this can cause pain in the toes, leg, knee, or hip.

Diagnosis

The os trigonum bone is normally an incidental finding during an evaluation for foot pain or ankle pain. Sometimes, if you have persistent ankle pain, your healthcare provider might order an imaging test to see if you have an os trigonum.

Imaging tests that can identify an os trigonum bone:

• X-ray: An os trigonum may be seen on an X-ray, which is a test that visualizes the structure of the bones. This test cannot tell whether an os trigonum is the cause of your pain, but it can rule out other causes of pain, such as a bone fracture.
• CT Scan: This test can be used to assess bone structure and swelling, and it can identify an os trigonum. It may support a diagnosis of os trigonum syndrome and rule out some other potential causes of pain, such as an abscess.
• MRI Scan: An MRI can be helpful for identifying bone structure, as well as fluid accumulation in and around the abnormal bone. It can be used to diagnose os trigonum, as well as to support a diagnosis of os trigonum syndrome, or other problems, like tendonitis.

Os trigonum syndrome is diagnosed based on symptoms, physical examination, and imaging tests. You might have tenderness above the inflamed bone when your healthcare provider examines you. In some cases, you could have swelling at the back of your foot.

Other possible causes of pain in the back of the ankle include arthritis, Achilles tendon problems, or retrocalcaneal bursitis.

Treatments

Os trigonum syndrome treatment starts with simple, nonsurgical strategies. Treatment may include a combination of:

• A few days of rest from the activity causes pain.
• Home exercises or physical therapy to correct ankle alignment or strengthen muscles in your feet and legs.
• Icing several times a day to decrease swelling.
• Immobilization with a walking boot restricts foot and ankle movement so the injury can heal.
• NSAID’s.
• Steroid Injections.

These strategies are effective for most people with this syndrome. But if you still have symptoms after several months of treatment, surgery may be necessary to continue certain activities.

Surgery to remove (resect) the os trigonum and surrounding tissue can be done arthroscopically or with an open incision. Recovery takes one or two months, and athletes often return to full activity levels within six months.