Up To 21% Of People May Have An Extra Foot Bone. Could You?

Finding accessory bones, otherwise known as ossicles, when looking over our patients’ radiographs is not an uncommon occurrence here at The Podiatrist. Many people will go throughout their lives never knowing that they have an accessory bone or two. After all, if it’s not painful, why would you look?

For others, unfortunately, their extra bone can cause pain, discomfort, and make them more vulnerable to other problems. Today, we’re sitting down to talk about accessory bones in the foot and ankle, what it means if you have one, and what you can do if it’s causing you pain.

Why do accessory bones in the feet develop?

Accessory bones are usually very small but solid bones that often develop when part of a bone separates during growth and development. The literature shows the prevalence of these bones ranging from 2-21% [1].

At birth, bones are largely soft and cartilaginous, forming into solid bone over time. A growing bone has multiple ossification centres, which is the first area of the bone that starts hardening into solid bone. When an ossification centre fails to fuse with the rest of the bone, or is prevented from doing so due to injury, it becomes an accessory bone.

Accessory bones are named after the bone they’re next to and have likely stemmed from. So, while you have a bone called the navicular in your foot, you may also have an accessory navicular.

Does this mean that accessory bones can form from any bone?

In the foot and ankle – yes, you may develop an accessory bone at any one of the 26 bones. With this being said, some accessory bones are significantly more common than others. These are:

The one at the back of your heel (Os Trigonum)

This is the accessory bone to the talus, one of the two bones that comprise your ankle joint alongside your heel bone (calcaneus). As such, it sits right behind the ankle joint, close to the Achilles tendon, with a fibrous band to connect it to the talus bone.

If this accessory bone becomes symptomatic, you may feel an ache at the back of the heel, or a pain when pointing your foot downwards, as this often creates a tighter space for the os trigonum bone to sit in. This makes it more noticeable in those who participate in ballet, gymnastics, basketball and soccer.

The one at your fifth toe (Os Vesalianum)

This is the accessory bone to the fifth metatarsal (the long bone of the foot). It sits at the ball of the foot, at the 5th toe joint. When symptomatic, pain and tenderness are felt in this same region, on the outside of the foot.

This bone typically does not become painful on its own, but in association with an injury to this area. This makes it important to accurately differentiate between a resultant fracture, or the longstanding presence of the accessory bone.

The one on the inside of your foot (Os Tibiale Externum)

This accessory bone is best known as the accessory navicular. Your navicular is located on the inside border of your foot, just after the ankle joint. It is often embedded in the posterior tibial tendon, which plays a major role in walking, turning the foot inwards, and enabling you to stand on your tip-toes.

Studies have shown that accessory naviculars are more common in women, and often develop in both feet. When symptomatic, pain develops in the arch and is exacerbated by weight-bearing activities like walking and running.

The one on the outside of your foot (Os Peroneum)

This accessory bone is located on the outside border of your foot, up from the ankle but before the middle of the foot. This is where the cuboid bone is located. This bone sits within the peroneus longus tendon, and as a side-effect, may weaken the tendon.

When symptomatic, patients experience pain on the outside border of the foot. Sometimes, the pain will have no recognisable cause, while at other times, tight footwear can rub against the outside of the foot and irritate the bone and tendon.

Is an accessory bone always painful?

No. As we mentioned, you may live your whole life without knowing that you have accessory bones, or you may only notice them coincidentally on an x-ray when looking at other problems. When pain does start, it is usually localised to the area of the accessory bone and any tendon in which it is embedded.

How are accessory bones treated?

Treatment starts with ice, rest, careful mobility (walking), anti-inflammatory medications and physical therapy. If the accessory bone has irritated the surrounding tendon, this can help reduce the inflammation and hence symptoms. If the accessory bones need removing, surgery can be performed to remove the bone and repair the tendon.

Accessory bones can be difficult to diagnose, but we can help

Accessory bones may appear like avulsion fractures (fractures where part of the bone breaks off), and may sometimes be difficult to detect on an x-ray. This can make it challenging to diagnose. If you’re reading this and are wondering if the cause of your ongoing pain could be an accessory bone, we can help.

• Our experienced podiatry team performs comprehensive assessments, and can refer you for x-rays to look for accessory bones in the areas you are experiencing pain.