The Os Trigonum is an accessory bone located in the posterior(back)and lateral(outside)of the talus (ankle bone). The term Os Trigonum Syndrome is used for patients that have pain and swelling within the area of the Os Trigonum. This portion of bone usually becomes fused to the body of the talus. In some individuals the bone remains a separate portion of bone and never fuses, which can cause no problems.

Symptoms of a os trigonum syndrome usually present following a traumatic event. Trauma from a sprained ankle, or direct hit may cause a fracture or inflammation in the area producing symptoms. Common symptoms are pain with activity, swelling in the area of the back of the ankle. It usually feels better keeping all weight off the foot and the foot placed in equinus (like walking on the tip-toes). Sometimes with os trigonum syndrome, if the big toe is dorsiflexed (raised up) pain is elicited in the back of the ankle. This is due to a tendon that passes by the posterior lateral process of the talus that enters the bottom of the foot and inserts into the big toe to allow its strong pull downward. The stretching of this tendon by raising the toe upward can produce a sharp pain when injured.

Causes of os trigonum is frequently due to an extreme plantarflexion of the foot. With an enlarged portion of bone at the posterior and lateral aspect of the talus the at extreme range of motion this portion can get crushed like a nutcracker effect between the other bones of the ankle.

Podiatric Care may include immobilization using a soft dressing, immobilization boot or cast. Your podiatrist may suggest absolutely no walking on this foot for a period of time. They may use anti-inflammatory oral medications or an injection of medication and local anesthetic to reduce the swelling. When you go to your doctor, x-rays are usually required to evaluate the structure of your foot and determine if a fracture has occurred. If the portion of bone is suspected fractured, it may never heal back to the body of the talus. Your podiatric physician may also recommend a surgical procedure to actually fix the problem of your foot as the os trigonum can be fixated with wires, screws, or pins to the body of the talus, or removed completely from the body.