Sometimes, feet do weird things. For instance, about 10% of the general population’s feet have decided that having an extra bone in the mix is a really great idea. This extra bone (or sometimes a bit of cartilage), is called an accessory navicular. It shows up in a tendon called the posterior tibial tendon (which is a fancy name – but just remember, it helps support the arch of the foot) on the middle of the inside of the foot, just above the arch. This extra little bone is present from birth, so it’s not something that’ll suddenly grow later in life.

Now, accessory navicular syndrome is when that extra bone starts causing issues with your shoe-wearing, or even the shape and function of your foot. It’s the syndrome you want to worry about, not necessarily the extra bone itself.

The majority of people with an accessory navicular experience no symptoms, since, for the most part, the little extra bone simply isn’t large enough to cause problems. Unfortunately, some people lose on ‘accessory navicular roulette,’ and the bone begins to mess things up with the foot. These problems usually show up sometime in adolescence, when bones and cartilage in the body are settling into their final shapes (although occasionally people make it all the way through childhood, only to start experiencing discomfort and pain in adulthood).

The catalyst for symptoms might be some sort of injury (such as a broken or sprained ankle), excessive activity, or irritation from where shoes are rubbing on the bony prominence the accessory navicular makes. These can irritate the bone, or make the tendon it’s embedded in (the posterior tibial tendon, remember?) inflamed and sore. Because the tendon is compromised in its ability to support the arch, accessory navicular syndrome almost always leads to flat feet, which is one very obvious symptom.

If you develop accessory navicular syndrome, you may experience a throbbing sensation or other types of pain in your midfoot or arch (especially while or right after you use the foot heavily, such as during exercise), and you may notice a bony prominence on the interior of your foot above the arch. This prominence may become inflamed, which means it will likely feel warm to the touch, look red and swollen, and will probably hurt.

Your podiatrist will most likely diagnose accessory navicular syndrome by making a visual study of the area, checking whether the shape of your foot and your ability to move it indicate there’s an accessory navicular lurking around. He or she may push on the prominence on your foot to check to see if it hurts, and may ask you to walk around in order to ascertain how your gait is affected.

In order to get a certain diagnosis, your podiatrist will need some way to see the inside of your foot, which will most likely involve getting X-rays, or possibly an MRI or some other scan of your foot’s interior.

Ideally, getting rid of the symptoms of accessory navicular syndrome will involve soothing the inflammation and irritation in your foot. So, for starters, your podiatrist may have you rest the area, allowing the inflamed tendon and bone to heal. This may be accomplished by wearing a cast or boot designed to keep you from moving the problem area. Your podiatrist may also suggest using ice to reduce the swelling and inflammation, and anti- inflammatory medications (like ibuprofen, or sometimes a cortisone shot or other steroid medication).

In order to strengthen your muscles to prevent further injury and to provide support to the foot, your podiatrist may also outline a physical therapy routine and prescribe orthotics. Orthotics will provide support to the arch of your foot, although they must be carefully crafted in order to make room for that pesky extra bone you’ve got poking about.

If your pain and discomfort don’t go away with treatments like these, then it may be time to consider surgery. If you decide to go through with it, your surgeon will probably remove the accessory navicular once and for all, and will tighten up the posterior tibial tendon in order to make it better able to support your arch. You’ll probably have to wear a cast for a several weeks, and a brace for some months after that, but with patience, you may be able to say goodbye to your symptoms.