What is the os trigonum?
The os trigonum is a tiny, additional bone in the foot. It is found on the back of the ankle and is a result of incomplete bone/ankle formation. During childhood, a part of the ankle joint called the talus bone is attached to the os trigonum by fibers. As the child grows and develops, the talus bone normally fuses with the os trigonum to create a small lump. In 3-15% of the population, however, the bones fail to fuse together and the os trigonum remains its own entity.
What is os trigonum syndrome?
Os trigonum syndrome is a disorder that causes pain in the back of the ankle. The os trigonum is usually imperceptible, as it is less than a centimeter in size and lacks any naturally sharp protrusions. Sometimes after trauma to the ankle, though, the bone can start causing pain, irritation, and stiffness. It is most commonly diagnosed in athletes, such as football players and dancers, who frequently point their feet downward.
What are the causes of os trigonum syndrome?
Os trigonum syndrome can occur when an individual with an unfused os trigonum suffers an ankle injury; repetitive or acute forced hyperplantar flexion is the most common cause of this disorder. Hyperplantar flexion means that the individual is pointing their foot downward with the ankle directed upward (think: a ballerina standing on her toes in pointe shoes.) Repeatedly or forcibly engaging the foot in this position can lead to a “nutcracker injury.” The os trigonum gets crushed between the ankle and heel bones, like a nut in the jaws of a nutcracker, and upon release the surrounding tissue is damaged, stiff, painful, and inflamed. This tissue damage can occur because of one extreme instance of hyperplantar flexion, or repeated and minor instances of hyperplantar flexion.
How is os trigonum syndrome diagnosed?
Individuals with os trigonum syndrome will usually present to the physician with pain and swelling in the back of their ankle. Radiography can be used to determine whether or not the person has the extra os trigonum bone. Additionally, anesthetic injections between the os trigonum and the ankle can suggest the presence of os trigonum syndrome if the injection provides significant relief to the patient. Other techniques such as foot manipulation, gait evaluation, functional assessment, etc. may be utilized to rule out additional pathology.
What are the symptoms of os trigonum syndrome?
Os trigonum syndrome primarily presents with pain, tenderness, and inflammation in the back of the ankle. Movement of the ankle may be impaired due to stiffness. Symptoms may worsen when pointing the foot downward in hyperplantar flexion or when pushing off of the toes during normal locomotion. Occasionally the individual may be able to feel the os trigonum as a hard lump in the back of the ankle.
How is os trigonum syndrome treated?
Conservative treatment methods are used to allow the soft tissue to heal. These include…
- Frequent rest and ankle elevation for four to six weeks
- Avoidance of activities that worsen symptoms
- Regularly apply an ice pack to the back of the ankle to reduce inflammation
- Use of NSAIDS as needed for pain and inflammation
- Physical therapy to strengthen the ankle and foot
- Softly stretching out the ankle on a regular basis
- Protective footwear for immobilization, ex. a boot
- Corticosteroid injections to reduce pain and inflammation
In more severe cases, if symptoms continue after conservative treatment, the os trigonum may need to be removed via surgical methods.
Image from Wikipedia