What Is Accessory Navicular Syndrome?
Accessory navicular syndrome is when an extra bone in the foot causes pain and other symptoms. The accessory navicular—also known as the os naviculare or os tibiale externum—is a small bone that extends from the navicular bone, one of the tarsal bones near the instep. About 14 percent of the population has an accessory navicular, and about half of the people with the extra bone have it in both feet.
Often, an accessory navicular causes no symptoms. When it does, however—the most common symptom being pain—it is known as accessory navicular syndrome. The posterior tibial tendon attaches near the navicular bone and accessory navicular, so tendon irritation is a common source of pain in accessory navicular syndrome.
Accessory Navicular Causes and Risk Factors
Accessory navicular is congenital—it is present at birth. The exact reason why some people have an accessory navicular is unknown. Theories include incomplete joining and abnormal separation of bones and connective tissue. There is likely a genetic component.
Accessory Navicular Syndrome Symptoms
For many people, having an accessory navicular creates no symptoms. When symptoms do occur, they usually appear in adolescence, when cartilage begins to calcify and harden into bone and many young people become more active.
Pain is the main symptom of accessory navicular syndrome. It can occur due to chronic irritation of the posterior tibial tendon (posterior tibial tendinitis, or PTT). Pain can happen from an injury to the area, activity and overuse or chronic irritation from shoes. Sometimes an inflamed red bump develops on the side of the foot.
Accessory navicular syndrome often appears among those who have flat feet.
Diagnosis of Accessory Navicular
Diagnosis starts with a physical exam and medical history. The doctor will ask about any symptoms and when they may have started, and may press on the side of the foot to check if there is any pain. X-rays can be useful in confirming or ruling out accessory navicular.
Accessory Navicular Syndrome Treatment
Accessory navicular(s) that do not cause pain need no treatment. Treatment for accessory navicular syndrome usually starts with conservative care, and the condition often requires nothing more.
Switching to softer shoes is usually the first-line treatment. If that doesn’t work, a custom-made orthotic insert may help. Other conservative measures can include:
- Rest from physical activities that aggravate the area
- Nonsteroidal anti-inflammatory medication to control PTT
- Physical therapy
If surgery is necessary, the Kidner procedure is the most common. This is where a surgeon removes the accessory navicular and reattaches the posterior tibial tendon with a screw. It is a fairly simple surgery—it takes approximately 45 to 60 minutes—that usually produces a good outcome (a relief from pain and no disability).
After the surgery a hard cast will usually be necessary to immobilize and protect the affected foot. For the first two weeks to a month after surgery, the patient will wear the cast and should not bear weight on the affected foot.
After approximately a month, the cast can be removed and replaced by a boot, and the patient will be able to begin to bear weight on the leg. About six weeks after surgery, the patient should be fully able to bear weight on the affected leg and can begin physical therapy. A full recovery may take up to six months, but patients can return to work or school far sooner.