OS Trigonum Syndrome – Causes, Symptoms & Treatment

OS Trigonum is an extra bone that might be found in some people and it grows behind the ankle bone talus. Almost 5 to 10% of population experience this bone and a painful condition caused by this bone is called as OS Trigonum syndrome. As it grows behind the talus and occupies a small space, it rarely causes any pain or discomfort.

But, repetitive ankle flexion can cause pain & stiffness which is termed as OS Trigonum syndrome. Athletes and ballet dancers who require frequent flexion of the ankle to perform their sports activity are more prone to this syndrome.

Here are the most common causes, symptoms, and treatment of OS Trigonum syndrome –

What is Os Trigonum?

Os Trigonum Bone

The ankle joint is made up of multiple bones and talus is one of the bones that helps to form ankle joint.

During development of talus bone, a small extra bone grows on posterior part of the talus, and it is known as Os Trigonum. It mostly occurs during the bone development and more common in the age group of 7 to 12.

So Os Trigonum is defined as a small piece of bone that grow behind the talus bone of ankle joint and may cause some discomfort in some people.

It is found that during an early stage of development of this bone; it is attached to talus bone with the help of fibrous tissue.

In most of the population, as time passes it get connected with talus bone and form a tiny bump of talus which commonly known as lateral tubercle.

But is some people it does not get attached with talus and remain as a stand-alone bone. It does not have any fixed shape, but in most of the cases it can be either oval, triangular or round and found to be less than one centimetre in length.

This stand alone bone do not create any health problems, but if ankle joint get injured or exposed to repeated stress & trauma then it may develop a set of symptoms which is known as ‘Os Trigonum Syndrome’ Some physicians call it as a posterior talar impingement

Causes of Os Trigonum Syndrome

As discussed earlier, Os Trigonum Syndrome is caused by constant stress and ankle injuries.

Excessive Use –

Excessive use of an ankle joint in some sports activity like running & ballet dancing can trigger the pain in the area of Os Trigonum.

Especially, repetitive plantar flexion of the foot leads to soreness & distress.

Ankle Trauma –

Ankle injuries that caused by excessive plantarflexion may result in this syndrome.

During plantar flexion, soft tissues from the backside of ankle joint get wedged between the talus and other bones of ankle joint and presence of Os Trigonum triggers inflammation of those tissues.

This kind of injuries are known as Nutcracker injuries, and mostly they are connected with the activities of joints.

Common Symptoms

The most common symptoms of this syndrome are as follows:

  1. Tenderness at back of ankle joint.
  2. Pain that becomes worse with movement.
  3. Swelling
  4. Hard Lump 


Usually, sign and symptoms point toward the Os Trigonum.

Often, a doctor will ask you to undergo an x-ray or MRI scan to differentiate this condition from other foot pain problems like Achilles tendonitis, fractures, ankle tendonitis, tarsal tunnel syndrome, etc.


The ultimate goal of treatment is to help the body heal itself by assisting tissues to relieve inflammation and pain. Treatment option can include several points as follows:

1. Enough Rest – Providing enough rest to ankle joint can help foot tissues to combat inflammation and aids the recovery. So your doctor may advise you to take rest for almost 5 to 6 weeks from all those activities that trigger pain like dancing, running etc.

2. Apply Ice – Applying ice for few minutes every day can help to reduce pain as well as inflammation. Never apply ice directly to the affected area, instead, take an ice bag and fill it with ice and apply it to the back of foot area for few minutes at a time and then wait for a couple of hours before you re-apply the ice bag.

3. Medicines – Doctor will prescribe some medication to alleviate pain and inflammation. Usually, he will start by prescribing anti-inflammatory pills like NSAIDs.

4. Steroid Injections – If pain does not subside with NSAID, the doctor will advise you to take steroid injections to relieve pain and inflammation.

Dr. Sachin

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