Foot & Ankle Surgery located in Fort Worth and Weatherford, TX

Os Trigonum Syndrome

The os trigonum is an extra (accessory) bone that develops behind the ankle bone (talus). It is connected to the talus (bone under ankle) by a fibrous band. This extra bone is present at birth; however during adolescence it does not fuse with the rest of the talus. A small amount of people have this extra bone.


Patients often do not know they have an os trigonum until an injury occurs. Os trigonum syndrome is triggered by an injury, such as an ankle sprain as well as activities or sports that frequently cause the downward pointing of the toes. The os trigonum can get squeezed between the ankle and heel bone. As the os trigonum gets loose, the tissue connecting it to the talus is stretched or torn and the area becomes inflamed.


  • Deep, pain in the back of the ankle, occurring mostly when pushing off on the big toe or when moving the big toe
  • Pain when when pointing the toes downward or moving the ankle downwards
  • Tenderness in the area when touched
  • Swelling in the back of the ankle


Os trigonum syndrome can mimic other conditions such as an Achilles tendon injury, ankle sprain, or talus fracture. Diagnosis of os trigonum syndrome begins with questions from your surgeon about the development of the symptoms.

X-rays are ordered to evaluate any bony abnormalities. An MRI will likely be ordered to evaluate the soft tissue around the ankle as well as the ankle and subtalar joint. This is to determine the extent of the pathology to the back of the ankle as well as determine surgical planning should surgery be warranted.

Non Surgical Treatments

Relief of the symptoms is often achieved through treatments that can include a combination of the following:

  • Rest. Limit the amount you are on the injured foot/ankle.
  • Immobilization. A walking boot may be used to keep the foot and ankle from moving and allow the injury to heal.
  • Ice. Apply an ice pack to the injured area, placing a thin towel between the ice and the skin. Use ice for 20 minutes and then wait at least 40 minutes before icing again.
  • Compression. An elastic wrap may be recommended by your surgeon to control swelling.
  • Elevation. The ankle should be raised slightly above the level of your heart to reduce swelling.
  • Physical therapy. Your surgeon may start you on a rehabilitation program to help with the pain and to assist in function and strengthening.
  • Medications. Nonsteroidal anti-inflammatory drugs (NSAIDs), may be recommended to reduce pain and inflammation. In some cases, prescription pain medications are needed to provide adequate relief.
  • Injections. Sometimes cortisone and local anesthetic are injected into the area to reduce the inflammation and pain.


Symptoms usually improve with non-surgical treatment. However, in some patients, surgery may be required to relieve the symptoms. Surgery typically involves removal of the os trigonum, as this extra bone is not necessary for normal foot function. Your surgeon will select the surgical procedure best suited for your case based on the type and severity of your condition.

Surgery is typically an outpatient procedure (day surgery) and scheduled at your convenience.

A splint or boot will be placed on your surgical foot/ankle after surgery. No weight to the surgical foot/ankle is advised until your surgeon encourages weight bearing.