Extra Bone In Foot Accessory Navicular

Overview
The accessory navicular also termed the os navicularum or os tibiale externum - is an extra bone or piece of cartilage on the inner side of the foot above the arch that attaches to the posterior tibial tendon within this area. This extra bone, present at birth, is not part of the normal bone structure and found in approximately 10% of the population. Some people with an accessory navicular may be unaware of the condition if symptoms are never experienced. But accessory navicular syndrome is a painful condition caused by aggravating the bone, the posterior tibial tendon or both.\Accessory navicular syndrome is an irritation of the accessory navicular and/or posterior tibial tendon. This irritation can be caused by shoe rubbing, trauma, excessive activity, or overuse and can cause problems with the shape and function of your foot. Many people with this disorder also have flat feet which puts more strain on the posterior tibial tendon. Some people are born with an accessory Navicular because during development, the bones of the feet sometimes develop abnormally causing the extra bone to form on the inside of the foot.



Causes
Most of the time, this condition is asymptomatic and people may live their whole lives unaware that they even have this extra bone. The main reason the accessory navicular bone becomes problematic is when pain occurs. There is no need for intervention if there is no pain. The accessory navicular bone is easily felt in the medial arch because it forms a bony prominence there. Pain may occur if the accessory bone is overly large causing this bump on the instep to rub against footwear.

Symptoms
This painful condition is called accessory navicular syndrome. Accessory navicular syndrome (ANS) can cause significant pain in the mid-foot and arch, especially with activity. Redness and swelling may develop over this bony prominence, as well as extreme sensitivity to pressure. Sometimes people may be unable to wear shoes because the area is too sensitive.

Diagnosis
To diagnose accessory navicular syndrome, medical staff ask about the patient?s activities and symptoms. They will examine the foot for irritation or swelling. Medical staff evaluate the bone structure, muscle, joint motion, and the patient?s gait. X-rays can usually confirm the diagnosis. MRI or other imaging tests may be used to determine any irritation or damage to soft-tissue structures such as tendons or ligaments. Because navicular accessory bone irritation can lead to bunions, heel spurs and plantar fasciitis, it?s important to seek treatment.

Non Surgical Treatment
Most cases of accessory navicular syndrome may be treated conservatively with some sort of immobilization. This should allow the fibrous tissue between the two bones to heal. If a patient is extremely flat footed (pronated) then I lean more towards an orthotic than a boot as my main goal is to keep the patient's foot from flattening out too much and thus reduce the strain on the two bones. Supplementation with ice, oral anti-inflammatory medication. If the patient is athletic sometimes we can keep them active with an orthotic, but other times they have to give up their sport for a period of time to allow the condition to heal.



Surgical Treatment
Once the navicular inflammation has lessened it is not necessary to perform surgery unless the foot becomes progressively flatter or continues to be painful. For these children, surgery can completely correct the problem by removing the accessory navicular bone and tightening up the posterior tibial tendon that attaches to the navicular bone. The strength of this tendon is integral to the success of this surgery as well as the arch of the foot. Following surgery the child is able to begin walking on the foot (in a cast) at approximately two weeks. The cast is worn for an additional four weeks. A small soft ankle support brace is then put into the shoe and worn with activities and exercise for a further two months.