Accessory Navicular Bone

An accessory navicular is an extra bone that forms in your foot. Healthcare providers sometimes call it by its Latin medical names, os naviculare or os tibiale externum.

Accessory is the medical term for something extra or unnecessary. The navicular bone is a small bone between your ankle and the top of the arch of your foot. So, an accessory navicular bone is an extra bone that grows near your navicular bone.

You might never know you have an accessory navicular. It often doesn’t cause pain or other symptoms. But they sometimes put extra pressure on the tendons or bones around them. This can make your foot hurt and increase your risk of some injuries.

Where is an accessory navicular located?

Accessory navicular bones form when your body mistakenly creates an extra bone near your actual navicular bone in the arch of your foot, near your ankle.

All of your bones start as cartilage when you’re a baby. That cartilage hardens into bone tissue as you grow and develop. If your body makes extra cartilage in your foot when you’re developing, it might harden into an accessory navicular.

Accessory naviculars can be genetic. That means if one of your biological parents has one, there’s a chance you will, too.

Healthcare providers classify them into three types based on their size and where they form:

• Type I: This type is embedded in the tendon that connects one of your calf muscles to the bones on the inner side of your foot and ankle (posterior tibial tendon). They’re small (2-3 millimeters, or less than an inch long) and usually don’t cause symptoms.
• Type II: These are triangle or heart-shaped bones that are around 12 millimeters long (around half an inch). They grow next to your regular navicular bone and connect to it with extra cartilage. They’re the most likely kind to cause symptoms.
• Type III: These are like type IIs that aren’t completely separate from your navicular bone. They’re an extra growth of bone that’s fused to the main navicular.

Accessory navicular syndrome

Having an accessory navicular usually won’t cause issues. But if it’s big enough or forms at the wrong angle, it can damage your posterior tibial tendon. Healthcare providers call this accessory navicular syndrome. If it constantly stretches or forces the tendon to move in an unusual way, the tendon can tear (rupture). But this is very rare.

Accessory navicular syndrome symptoms can include:

• Foot pain, especially near the inside edge of your foot’s arch
• Trouble walking, standing or putting weight on your foot
• Limping or pain that gets worse when wearing shoes
• Swelling
• Skin discoloration
• A bump on your foot you can feel and see

Accessory navicular syndrome can happen on its own, but you may be more likely to develop it after an injury like a foot or ankle sprain. Overusing your feet and ankles for physical work, sports or physically demanding hobbies can also increase your risk. Wearing shoes that are too tight can put extra pressure on an accessory navicular and lead to pain and other symptoms.

You can develop symptoms at any age. But accessory navicular syndrome usually affects teens. Your body changes quickly during adolescence. And that includes your bones. These rapid changes can increase the odds of issues near an accessory navicular bone.

Accessory navicular treatments

If you never experience pain or other symptoms, you’ll never need treatment. If you do, a healthcare provider may suggest:

• The RICE method: Taking a break from physical activities can help prevent extra stress and damage in your foot.
• Changing your shoes or wearing orthotics: You might need to wear different, more supportive shoes throughout your day. Your provider might suggest orthotics, too. These are custom-made or over-the-counter shoe inserts.
• Pain medication: You can probably manage pain and swelling with over-the-counter NSAIDs or acetaminophen. Your provider might give you a cortisone shot if you have more severe symptoms and other treatments don’t work.
• Immobilization: Your provider might suggest that you wear a cast or walking boot for a few weeks. This will support your foot and take pressure off it while it heals.
• Physical therapy: Strengthening the muscles in your legs and feet can help take extra pressure off your bones. A physical therapist will give you customized exercises and stretches based on your unique needs.
• Surgery: Most people don’t need surgery. But your provider may suggest it to remove the accessory navicular if it damages your tendons or other bones. A surgeon will repair the damaged tendons and remove the extra bone.