Pain on the inside of the ankle may be due to tibialis posterior tendonitis, midfoot arthritis, or a navicular stress fracture. A less common cause of inner foot pain is accessory navicular syndrome, also known as os naviculare. So what is accessory navicular syndrome, and how do we manage it?

What is an accessory navicular?

The navicular is a wedge-shaped bone connecting the ankle to the midfoot. During childhood, it has two ossification centres — one in the centre and one on the inside. In most people, these two centres fuse into a single bone. In about 10% of people, they don’t fuse, leaving two bones. The accessory navicular (os naviculare) is an extra bone that sits just inside the main navicular and is joined to it by cartilage.

Most people with an os naviculare never know they have one. Sometimes, though — after an ankle sprain, or from chronic rubbing against a shoe — pain develops on the inside of the ankle. We think the pain comes from the disruption of the cartilage between the two bones.

Accessory navicular syndrome symptoms

The common symptoms of accessory navicular syndrome are:

  • Pain on the inside of the ankle or midfoot
  • Swelling or inflammation next to the accessory bone
  • A visible prominence or lump over the accessory navicular

Diagnosis is based on the history and examination. There is usually tenderness over the accessory navicular bone. Some people with the accessory bone also have flat feet, which pull on the accessory navicular (through the tibialis posterior tendon) and cause more pain.

How is accessory navicular syndrome diagnosed?

Accessory navicular bone on X-ray, a cause of inner foot pain

Confirming the diagnosis with imaging and ruling out other causes is essential:

  • X-ray shows the extra bone on the inside of the navicular.
  • MRI shows swelling around the bones, suggesting disruption of the cartilage between them.
  • Ultrasound shows increased blood flow between the two bones and any involvement of the closely attached tibialis posterior tendon.

Accessory navicular syndrome treatment options

Treatment aims to settle the inflammation. We start with simple measures — regular ice and oral anti-inflammatories such as ibuprofen. Custom-made orthotics support the medial arch and reduce pressure on the navicular. An ultrasound-guided cortisone injection into the cartilage between the two bones can also help.

Best shoes for accessory navicular

We suggest shoes with a wide midsole and a supportive medial arch. New Balance shoes are often well-suited to people with this condition.

A cortisone injection for accessory navicular syndrome

Sometimes we inject to reduce the pain of the os naviculare. We use ultrasound to direct the needle to the exact spot between the two bones. This accuracy improves the injection’s effectiveness and reduces side effects such as skin thinning and tendon rupture.

Os naviculare surgery: pros and cons

If conservative measures fail, surgery can help. If the accessory navicular is small, we remove the bone. If it’s more prominent, removing the bone and reattaching the tibialis posterior tendon may be needed. Occasionally, a screw fixes the accessory bone to the main bone. You usually need to wear a cast and a walking boot after surgery.

Frequently asked questions about accessory navicular syndrome

What causes the pain in accessory navicular syndrome?

The pain usually results from disruption of the cartilage that joins the accessory bone to the main navicular, often triggered by an ankle sprain or repeated rubbing against a shoe. Flat feet make it worse because the tibialis posterior tendon pulls on the accessory bone.

Is accessory navicular syndrome the same as a navicular stress fracture?

No. An accessory navicular is an extra bone present from childhood; a navicular stress fracture is a crack in the main bone caused by overuse. Both cause inner-foot pain, so imaging (X-ray and MRI) is used to distinguish between them.

Do you need surgery for an accessory navicular?

Usually not. Most cases settle with anti-inflammatories, orthotics, and sometimes a guided cortisone injection. Surgery is reserved for pain that doesn’t respond to these measures.

What are the best shoes for accessory navicular syndrome?

Shoes with a wide midsole and good medial-arch support work best, as they reduce pressure on the accessory bone. New Balance is often a good option, ideally combined with a supportive orthotic.

Can you run with accessory navicular syndrome?

Often yes, once a flare has settled — with supportive shoes, orthotics, and sensible load management. Running through an acute flare tends to prolong it, so it’s best to calm the inflammation first.

Is accessory navicular syndrome linked to flat feet?

Yes. Flat feet increase the pull of the tibialis posterior tendon on the accessory navicular, increasing the load on the cartilage between the two bones and potentially triggering symptoms; therefore, arch support is an important part of treatment.

Final word from Sport Doctor London about accessory navicular syndrome

An accessory navicular is present in about 10% of people, but only a small number develop pain. We usually start with simple treatments — anti-inflammatory measures and custom-made orthotics — followed by an injection if needed. Surgery is reserved for cases that don’t settle.

If you have persistent inner-foot pain, Dr Masci can assess you in London, including an ultrasound in the clinic. Contact the team here or call +44 (0) 203 488 0350.

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