Os Trigonum Syndrome

Os trigonum syndrome (posterior ankle impingement) can affect people with an extra bone behind the ankle called the os trigonum. Injury or repetitive stress can lead to ankle pain and stiffness. It’s more common in runners, dancers and soccer players. Rest and other strategies often help, but surgical removal of the bone is an option.


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.

An os trigonum is congenital, meaning a person is born with the extra bone. It may happen in one or both feet. The os trigonum attaches to your talus bone (lower part of your ankle joint) by thick tissue called cartilage, so it doesn’t move. Between 15-30% of people have an os trigonum and the vast majority of people who have an os trigonum don’t have any symptoms.

Posterior means behind, and impingement means pressure or pinching.

Who might get os trigonum syndrome?

A painful os trigonum can occur from trauma, such as a fall or other accident, or repetitive stress on the back of your ankle can trigger the syndrome. For example, posterior ankle impingement is more common in ballet dancers and people who play kicking sports like soccer where the foot is regularly forced downwards. It also occurs more frequently in people who walk or run downhill a lot.


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Symptoms and Causes

What causes posterior ankle impingement?

Os trigonum syndrome happens when a person has the 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 pulls away from its point of attachment. This can stretch and tear the surrounding tissue, causing irritation, inflammation (swelling) and symptoms.

What are the symptoms of os trigonum syndrome?

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 and Tests

How is posterior ankle impingement diagnosed?

To assess ankle pain, a healthcare provider will:

  • Ask you about your symptoms and activities.
  • Discuss your medical history, including any injuries.
  • Stretch, rotate, flex and move your foot and ankle to see what hurts and what doesn’t.

Os trigonum syndrome can produce symptoms similar to other conditions, such as an Achilles’ tendon injury or talus fracture. Your healthcare provider will often order imaging tests to confirm the presence of the os trigonum and rule out other causes. These tests may include:

Management and Treatment

How is posterior ankle impingement treated?

Posterior impingement syndrome ankle treatment starts with simple, nonsurgical strategies. Treatment may include a combination of:

  • A few days of rest from the activity causing pain.
  • Home exercises or physical therapy to correct ankle alignment or strengthen muscles in your feet and legs.
  • Ice several times a day to decrease swelling.
  • Immobilization with a walking boot, which restricts foot and ankle movement so the injury can heal.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs).
  • Steroid injections.

These strategies are effective for most people with posterior ankle impingement. 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.



How can I prevent posterior ankle impingement?

There’s no way to prevent the development of an os trigonum bone. But if you have one (or two), you may be able to reduce your risk of developing the syndrome by avoiding ankle injuries and activities that include repetitive pointing of your toes.

Outlook / Prognosis

What can I expect if I have os trigonum syndrome?

Most people with os trigonum syndrome recover well with rest and noninvasive treatments. But the symptoms may return if you start the triggering activity again.

Living With

How do I take care of myself?

To protect your ankles from injury:

  • Always wear proper footwear for the activities you’re doing. Replace footwear that’s damaged or worn out.
  • Avoid uneven surfaces. Examples include hills when running, uneven grass for soccer or a damaged floor in a dance studio.
  • Consider using a brace or tape to stabilize the ankle if you’re prone to ankle injuries.
  • Increase exercise intensity gradually over time. For example, if you’ve never played soccer, don’t suddenly play for three hours every day. Start with brief intervals and increase the time and intensity slowly.
  • Learn and practice proper techniques, especially for running, kicking and dancing.
  • Listen to your body. If something hurts, stop.
  • Warm up before any physical activity and stretch afterward.

Additional Common Questions

What is the difference between anterior and posterior ankle impingement?

Posterior ankle impingement syndrome occurs in the back of your ankle when painful, inflamed tissue in this area gets pinched while your foot is pointing downwards. Having an extra bone (os trigonum) in this area may increase the likelihood of having symptoms. Anterior ankle impingement syndrome occurs over the front of your ankle. It develops because of bone spurs in the front of your ankle joint or toward the bottom of your shin.

A note from Cleveland Clinic

Posterior ankle impingement syndrome causes pain in the back of your ankle. It often occurs when an extra bone in the ankle becomes irritated. This condition is os trigonum syndrome and is common in runners, dancers and people who play kicking sports. If you have ankle pain, talk to your healthcare provider about ways to treat the symptoms and prevent injuries.

Medically Reviewed

Last reviewed on 11/09/2022.

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