Accessory navicular (extra foot bone)

What is an accessory navicular, and how common is it?

An accessory navicular is an extra bone on the inner side of the foot, next to the navicular bone¹. It's one of the most common extra bones in the foot, found in about 4–14% of people¹, with estimates up to 21%². Most people with one have no symptoms, so it's usually found by chance².

Occasionally it becomes painful, which is called accessory navicular syndrome². Then the inner midfoot can be tender, swollen or red², and the pain tends to come and go with activity¹. If it's found by chance and doesn't hurt, it usually needs no treatment.

What causes it, and who gets it?

In children, the bump rubbing on the shoe is the most common cause of pain³. In adults, a twisting injury is more often the trigger³. Pull from the tendon and friction at the join may also play a part⁴.

It often starts in the teenage years and runs in families, and genetics is thought to play a large part¹². It often goes with flat feet, but which causes which isn't clear, so don't assume treating one fixes the other²⁵.

It helps to note which activities, shoes or injuries bring the pain on.

What does it feel like, and how is it diagnosed?

The usual picture is a tender bump on the inner midfoot, which can look red or swollen²⁶. It tends to hurt with walking, sport or shoes that rub on it, and it comes and goes with activity⁶¹. It often starts in the teenage years, especially in teenagers who play sport⁷¹.

A podiatrist or doctor can usually diagnose it from your history and an examination, with an X-ray to confirm⁴¹. The bump is usually easy to feel¹.

A recent injury or bruising can point to a broken bone instead, which can look similar²³. A child's inner foot pain or limp shouldn't be assumed to be this condition⁸.

What helps first?

Once the pain has been checked and is thought to come from the bone, non-surgical care comes first²⁴⁸⁹.

• Ease off what hurts. Cut back on activities that bring the pain on, then build back up gradually¹.
• Wear supportive shoes that fit well and don't press on the bump⁴.
• Ask about arch supports. A podiatrist can advise on arch supports or custom orthotics (shoe inserts)²¹.
• Use ice².
• A boot or cast is sometimes used briefly. Follow your clinician's advice on how long¹.

Anti-inflammatory medicines (NSAIDs) call for particular care in children²⁴.

These steps aren't for a limp or foot pain with warning signs or no clear cause⁸⁹.

What helps if that isn't enough?

If your pain continues despite non-surgical care, surgery to remove the extra bone or the painful part may be the next step⁶⁷. A flat foot needs to be dealt with at the same time¹⁰.

Before any operation, the planned procedure and the reasons for it, the risks, what rehabilitation involves and when you or your child can return to sport are all points that can be explained beforehand.

How long does it take to get better, and can it come back?

In growing children, the type of accessory navicular appears to change as the skeleton matures, and a Type II is likely to develop into a Type III over time⁶. Joining doesn't necessarily mean the pain has gone⁶⁷. How long care takes, and whether anything stops the pain coming back, isn't clear yet, and the findings give no evidence-based answer on how long to keep using orthotics or exercises.

For children with flat feet, choosing suitable, well-fitting shoes and helping them keep to a healthy weight as the arch develops are sensible general steps¹¹. Return to sport gradually if the pain comes back.

What can make it serious?

• Your pain is getting worse, or doesn't settle with rest, less activity or pain relief.
• You have pain at night or at rest that doesn't settle.
• Your child has a limp that hasn't improved after a week, limps without pain, or doesn't want to put weight on their foot.
• Your child has a fever with a limp or a painful, red, hot or swollen joint, or seems very unwell with foot or leg pain.
• Your child suddenly has severe pain in one joint and is limping.
• You can't put weight on your foot or take four steps after an injury.
• You think you may have broken a bone in your foot or ankle in an injury, for example you heard a crack, or it swelled or bruised badly within minutes.
• Your child has hurt their foot or toe and it may be broken (in children a break can look like a sprain).