Os Trigonum: What You Need to Know

Do you have recurring ankle pain, especially when walking or extending your ankle or heel? You might be among the roughly 10% of people with an extra or “accessory” foot bone called the os trigonum.

What is the os trigonum?

The os trigonum is a tiny bone that forms behind the talus, or ankle bone. Although the os trigonum is present at birth (congenital), it usually doesn’t cause any symptoms until adolescence, when a tiny portion of the talus doesn’t fuse normally with the remainder of the ankle bone, isolating a small portion of bone which forms the separate os trigonum. In a few people, the os trigonum may become partially fused, forming a prominence at the back of the ankle. The bone can range in size and shape, appearing as a small, flat bone or a larger, rounded prominence. Sometimes, the os trigonum causes no symptoms and remains undiagnosed; but in adolescents who are active including student athletes and dancers, the accessory bone can irritate the soft tissues that surround it or cause a painful impingement (pinching) of other tissues. Often, the tiny bone becomes compressed or “crunched” by the ankle and heel bones on either side of the os trigonum, resulting in an “pinching” effect sometimes referred to as a “nutcracker injury.”

What symptoms and issues are associated with the os trigonum?

Os trigonum symptoms are far more common in dancers, swimmers, high jumpers and other athletes who repeatedly point their toes and place repetitive pressure on the toes that transfers force to the ankle area. When symptoms are present, they can include:

  • pain and aching deep in the back portion of the ankle, especially when walking or pointing the toes
  • tenderness in the back of the ankle when the area is pressed or rubbed
  • swelling in the back of the ankle or near the Achilles tendon
  • decreased range of motion and movement when pointing the toes

How is os trigonum treated?

Because the symptoms of os trigonum can mimic other common foot and ankle injuries like Achilles tendon injuries, sprains and even fractures, a careful physical exam followed by x-rays or other imaging tests are commonly used to confirm diagnosis prior to treatment. Once the os trigonum has been identified as the cause of symptoms, treatment can include nonsurgical management with rest and immobilization of the ankle, including the use of a special boot or splint to provide support to the joint while inflammation subsides and the injured soft tissues heal. Using an ice pack may also help decrease inflammation and pain. Oral medications and injections of corticosteroid medications into the affected area can also be very effective in relieving symptoms and helping inflammation subside. When these approaches fail to provide long-term or meaningful relief of symptoms, surgery may be needed to remove the os trigonum so impingement, pressure and painful symptoms do not occur. Following surgery, physical therapy can help restore range of motion and flexibility to the joint.

Will I need surgery?

Traditional surgical intervention involves an open, often extensive approach resulting in more scar formation and longer recovery.  At Nilssen Orthopedics we have developed an arthroscopic approach through two small incisions allowing patients a much quicker return to sport or activities of daily living.

If you’re having ankle pain or if you’ve already been diagnosed with os trigonum, the next step in treatment is to schedule an exam and evaluation with the Nilssen Orthopedic Center. As a top, multidisciplinary medical treatment and research facility in Pensacola, Fl., the Nilssen Orthopedic Center specializes in the diagnosis and treatment of ankle and foot injuries, offering both nonsurgical and surgical approaches as needed based on each patient’s individual symptoms, medical needs, lifestyles and treatment goals. As the first dedicated orthopedic sports medicine-based foot and ankle clinic in the United States, the center offers state-of-the-art care and innovative treatments aimed at providing every patient with individualized care for optimal results. Click below to schedule your evaluation and take the first step toward better foot and ankle health.


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