There are normally 28 bones in the foot. Some people have “extra” bones called accessory bones. There are specific accessory bones that are known and named and common. One of these bones is called an Accessory Navicular bone or Os Tibiale Externum. When it is present, it sits just behind the midfoot bone that is on the inside of the arch (navicular bone). The Posterior Tibial tendon surrounds this bone as it comes from the leg and ends in the navicular bone.
Some patients that are born with this bone will develop a flattened foot type over time, as the tendon attached to the bone weakens leading to the arch weakening. The arch can then get fatigued and painful over time. This may lead to Posterior Tibial tendon Dysfunction. Early treatment is needed to strengthen the tendon through physical therapy and rest and custom molded orthotics.
A severe foot sprain can dislodge or fracture the extra bone causing severe pain and difficulty walking. Early treatment with rest in a special walking boot is needed.
In chronic cases of damage to the extra born and the tendon, surgical removal of the accessory bone and repair of the tendon may be needed.