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Os Trigonum Syndrome: Causes, Symptoms, and Treatment

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Os trigonum syndrome is characterized by inflammation and pain at the region of the os trigonum bone, thus resulting in limitations in routine activities.

Written by

Dr. Varshini

Medically reviewed by

Dr. Rishabh M. Hegde

Published At October 31, 2023
Reviewed AtMay 6, 2024


Os trigonum syndrome, or posterior ankle impingement syndrome, a condition characterized by pain and limited mobility in the ankle joint, stems from an overlooked culprit - the os trigonum. This small, extra bone located at the back of the ankle can become irritated or impinged, leading to discomfort and functional impairment.

What Is Os Trigonum Syndrome?

Os trigonum syndrome occurs when the os trigonum, a tiny bone positioned behind the ankle joint, becomes irritated or impinged. This bone is present in approximately seven to 14 percent of the population and usually develops during adolescence. In most cases, the os trigonum is harmless and causes no issues. However, it can become problematic when it causes pain and functional limitations.

What Are the Causes of Os Trigonum Syndrome?

Certain activities and anatomical factors can contribute to the development of os trigonum syndrome. It includes:

  • Some individuals have a natural anatomical variation where the os trigonum bone fails to fuse with the rest of the talus bone during growth and development. This results in the presence of an extra bone behind the ankle joint, which can lead to impingement.

  • Activities that involve repetitive extreme plantar flexion (pointing the toes downward) can strain the posterior ankle structures and exacerbate os trigonum syndrome. Sports such as ballet, soccer, gymnastics, and activities that require frequent tiptoeing or pointed-toe positions can increase the risk.

  • Ankle injuries, such as ankle sprains or fractures, can cause this syndrome as these injuries can displace or impinge the os trigonum bone.

  • Exercises and routine activities that put excessive stress on the posterior ankle, like repetitive jumping or running, can contribute to the development of os trigonum syndrome.

  • Individuals with chronic ankle instability, either due to previous injuries or inherent laxity of the ligaments, may be more prone to develop os trigonum syndrome. The instability can lead to abnormal movement patterns and increased stress on the posterior ankle structures.

  • Structural misalignments, such as flat feet (pes planus) or high arches (pes cavus), can also cause this syndrome.

What Are the Symptoms of Os Trigonum Syndrome?

  • Pain in the back of the ankle, just behind the joint, is the most prominent symptom of this syndrome. It can be a deep, achy sensation with stabbing and sharp pain.

  • The affected area may be tender to touch. Palpation of the posterior ankle, specifically over the os trigonum bone, may elicit pain or discomfort.

  • Os trigonum syndrome can result in reduced ankle mobility, particularly when the toes point upwards. Individuals may also experience difficulty or feel a sensation of impingement during the movement.

  • Activities that involve extreme plantar flexion of the ankle joint can worsen the symptoms. Actions such as standing on tiptoes, performing in ballet, or pushing off forcefully during sports movements can elicit pain and exacerbate the condition.

  • In some cases, there may be mild swelling around the back of the ankle joint. The swelling is localized and may be accompanied by localized warmth or redness, indicating inflammation of the particular region.

  • The discomfort, paining sensation, and restricted movements associated with os trigonum syndrome can affect daily activities and sports performance. Walking, running, jumping, and other weight-bearing activities may be challenging and painful.

How to Diagnose Os Trigonum Syndrome?

Common investigations done to diagnose the condition include:

  • Physical Examination: A healthcare professional, such as an orthopedic specialist or a sports medicine physician, will begin by conducting a physical examination. They will evaluate the affected ankle, assessing the range of motion, checking for tenderness and swelling, and palpating the posterior ankle area to identify any areas of discomfort.

  • Medical History: History of symptoms, the location, duration, factors that worsen or alleviate the pain, history of any previous ankle injuries, and the frequency and intensity of physical activities engaged can help diagnose the condition.

  • X-Rays: X-rays provide detailed images and can visualize the os trigonum bone, its size, and any associated bony abnormalities or signs of impingement.

  • Magnetic Resonance Imaging (MRI): It helps in imaging the muscles and tendons around the os trigonum bone and helps in identifying any inflammation or deformity surrounding the bone. It also evaluates the extent of impingement.

  • Ultrasound: In some cases, an ultrasound may be used to visualize the os trigonum, assess the surrounding soft tissues, and detect any signs of inflammation or impingement.

How Is Os Trigonum Syndrome Treated?

The treatment of os trigonum syndrome depends on the severity of symptoms and the individual's goals. Non-surgical approaches are usually attempted first and may include:

  • Avoiding activities that aggravate the symptoms and giving the ankle time to heal.

  • Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) are prescribed for managing pain and inflammation. In some cases, a corticosteroid injection may be recommended to reduce inflammation and provide temporary pain relief around the os trigonum bone region.

  • Specific exercises can help improve ankle flexibility, strengthen supporting muscles, and reduce symptoms.

  • In severe cases, immobilization in a cast or walking boot may be necessary to allow the ankle to rest and heal.

If non-invasive measures prove to be ineffective, or in cases of persistent or recurrent symptoms, surgical intervention may be considered. The surgical procedure, known as an os trigonum excision, involves removing the os trigonum through a small incision. After surgery, a period of rest, physical therapy, and a gradual return to activity are typically recommended.

What Is the Rehabilitation Process for Os Trigonum Syndrome?

  • Prevention: Preventing os trigonum syndrome involves taking precautions during activities that involve repetitive extreme plantar flexion. It is essential to maintain flexibility, strength, and proper technique. Adequate warm-up exercises, regular stretching, and strengthening of the calf muscles can help reduce the risk of developing this condition.

  • Rehabilitation: Rehabilitation following treatment, whether conservative or surgical, is crucial for a successful recovery. Physical therapy plays a significant role in restoring ankle strength, flexibility, and function. Rehabilitation programs typically include a combination of stretching, strengthening exercises, balance training, and gradual return to sports or activities.


Os trigonum syndrome can cause significant pain and functional limitations in the ankle joint, impacting daily activities and sports performance. It is better to consult a physician at an early stage to manage the condition. With proper prevention strategies and rehabilitation, individuals can recover from os trigonum syndrome and return to their regular activities with reduced discomfort and improved ankle function.

Dr. Rishabh M. Hegde
Dr. Rishabh M. Hegde

Orthopedician and Traumatology


os trigonum syndrome
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