Os Trigonum Syndrome


An os trigonum is an extra bone at the back of the heel that is present in up to 15% of people. While many people will go throughout their lives not knowing this bone is present, it can occasionally become painful and inflamed.


The os trigonum bone is approximately the size of a pebble and sits right behind your ankle (as pictured). It is connected by thick tissue to a bone called the talus which is one of the large bones forming your ankle joint, and extending back behind the ankle.


Os trigonum syndrome develops when the bone and its surrounding tissues become irritated and inflamed, producing painful symptoms. The reason for the irritation and inflammation is that certain movements of the foot can trap and compress the bone and its surrounding tissues, causing painful damage. This is nicknamed the “nutcracker phenomenon”, wedging the os trigonum between the ankle bones and the back of the tibia (shin bone). This wedging is most often caused by movements where the toes are pointed downwards, lifting the back of the heel (and the accessory bone) upwards, such as:


  • Pointing the toes, which is often seen in sports like ballet, or when frequently kicking soccer balls
  • Downhill running
  • Ankle sprain injuries
  • Trauma that forces the foot downwards
  • Injury to the back of the heel directly to the region of the os trigonum bone can also cause this syndrome.


When assessing os trigonum syndrome, we look for pain and tenderness at the back of the heel that will likely feel worse when the toes are moved downwards and the heel is lifted up. Symptoms tend to worsen with physical activity and improve with rest. Sometimes, simply moving the big toe can produce pain at the back of the heel because one of the tendons that attaches to the big toe runs close to the os trigonum at the back of the ankle.


Can You Fix It?

Yes. The true problem here is not the presence of the accessory bone, but that the bone and surrounding tissues have become damaged and inflamed. Our podiatrists will work to help alleviate your painful symptoms, allow the damaged tissues to heal, and then help you put the right measures in place to reduce the risk of this recurring in the future.


Os Trigonum Syndrome Treatment

The first step in treating os trigonum syndrome is to confirm with medical imaging both the presence of the os trigonum bone and which of the surrounding tissues have been affected. Os trigonum syndrome shares many symptoms with other conditions like bursitis, so it’s important to rule out any other pathologies. 


Once we have a complete picture of the extent of the injury, using ice, rest, keeping the foot elevated and using non-steroidal anti-inflammatory medications (NSAIDs) can help reduce your immediate pain so you can feel more comfortable. The next goal is to allow the tissue damage to heal so the swelling and pain can resolve and you can get back to normal daily function. In order to achieve this we may use:


  • Custom foot orthotics: our podiatrists may prescribe a custom pair of orthotics using a 3D foot scan paired with a comprehensive assessment to best support your foot and ankle.
  • Footwear advice or modifications: wearing the right shoes plays a critical role in your recovery because in any shoes that have a heel, even if it’s a small one, will angle your toes downwards and bring the back of your heel bone up, risking the nutcracker effect and further damage. We’ll advise you on the best shoes to wear throughout your recovery. It is important to avoid all high heels – and remember that even sneakers can be subtly heeled.
  • Immobilisation: in some cases, it may be necessary to immobilise your foot using a boot or brace. In this case, we will discuss your options and help you get the best option for your unique circumstances.
  • Rehab program: as your foot heals and your symptoms settle, we may introduce isometric and eccentric exercises for the lower leg muscles. Stretching exercises may also be prescribed.


We achieve good treatment success following these principles. In very few cases, if the symptoms are not improving how we’d expect, we may refer for steroid injections or surgery.



An x-ray has uncovered an os trigonum, but I am not experiencing any heel pain. Should I be concerned?

If you’re currently asymptomatic, then you should not be concerned, as having an extra bone is not a problem – unless it becomes painful. Having this information may mean that you may approach exercise that involves pointing the toes with more caution, and listen to your body if any pain subsequently develops.


If my os trigonum pain is severe, should I jump straight to surgery?

In most cases, we are able to get good results and relief for our patients without surgery. We always recommend trying non-surgical measures first as surgery places a great demand on your body, and isn’t without its risks, limitations and recovery time.


Can I use ice for os trigonum, given it’s a bone?

As the source of your pain is not your accessory bone but the surrounding tissues which have become damaged and inflamed, yes, you can use ice if you’re experiencing pain and swelling at the back of your heel. Apply ice for no more than 20 minutes, through a towel or other cloth, and repeat 3-4 times per day. 


Does ACC cover treating os trigonum syndrome?

If your injury was sustained as a result of an accident, then you may be eligible for ACC. We will fill your paperwork and submit a claim, it is up to ACC whether or not you are covered.