Accessory Navicular Syndrome

Many people learn at some point in their lives that there are 206 bones in the body. This is somewhat true. There can be many small accessory, or extra, bones that are not counted in that number. The number of accessory bones a person has varies from person to person. Some, like the patella or knee cap, are very well known and pretty much everyone has them. Others are much less common.

 

If you include two accessory bones called sesamoids that most people have, there are normally 28 bones in each foot. Over half of the bones in your body are in your hands and feet. The number of joints in your hands and feet allows them to move in complex ways. It also means there are a lot of joints that can become damaged or arthritic.

 

There are ossification centers, or growth plates, in our bones. As kids and adolescents grow, those growth plates close. Many bones have only one ossification center, but some bones have secondary ossification centers as well. Accessory bones form when secondary ossification centers don't close normally. This results in an “extra bone.” Sometimes a soft tissue bridge will form between the accessory bone and the bone from which it was formed. It is important to keep in mind that these are normal anatomic variances and not a deformity. They are sometimes misdiagnosed as fractures on x-ray as well. The same accessory bones are usually found on both sides of the body. If there is a question regarding whether there is a fracture or an accessory bone, taking an x-ray of the other side will often help.

 

Most accessory bones do not cause any pain or other issues. In these cases, they are normally found incidentally when an x-ray is taken for some reason. In the foot, the most commonly painful accessory bone is found on the inside of the foot near the arch. It is called the accessory navicular, os navicularum, or os tibiale externum. An accessory navicular is present in an estimated 5-14% of all feet.

 

There are three types of accessory naviculars. The first type is small, less than 2-3mm in diameter, and is contained within the posterior tibial tendon near its attachment point on the inside of the foot at the navicular bone. This type is rarely painful because they are not attached to the navicular bone at all. The second type are larger and are attached to the main body of the navicular bone via a fibrocartilagenous, a type of soft tissue, bridge. These are the most commonly symptomatic. The third type has a bony fusion to the body of the navicular. This type often appears to be an extremely large navicular bone and is rarely painful but may cause shoe irritation.

 

An injury to this area, shoe irritation, or overuse especially in a person with flat feet can cause the accessory navicular to become painful. This is known as accessory navicular syndrome. When walking, the posterior tibial tendon pulls on the navicular bone. When there is an accessory navicular with a fibrous connection to the navicular, the tendon pulls on that connection and this can cause inflammation and pain. Symptoms normally occur anywhere between adolescence and adulthood and are aggrevated by activity. While the accessory bone can be diagnosed via x-ray, an MRI may be ordered to assess the tendon for tearing.

 

The treatment options for accessory navicular syndrome include shoe modifications, orthotics, physical therapy to reduce inflammation and pain, anti-inflammatory medications, ice, rest and immobilization of the foot. There posterior tibial tendon pulls with every step you take, so immobilizing the foot and ankle in a walking boot reduces the strain of the posterior tibial tendon on the navicular where it inserts in the foot. I personally do not recommend cortisone injections for any issue involving a tendon because there is a risk of the injection causing a tendon rupture, especially if multiple are given. Cortisone injections are a great tool we have to help reduce inflammation but they are not without risk and can also cause soft tissue and cartilage damage if overused.

 

If conservative treatment fails to alleviate the pain from the accessory navicular syndrome, surgery may be necessary. Surgical treatment options include removing the accessory navicular and repairing the posterior tibial tendon. Sometimes, the tendon needs to be repaired or reattached to the navicular bone after the accessory bone is removed. There are a variety of methods used to do this.

Author
Dr Katie Evans Dr Katie Evans writes a monthly column in the Hometown Focus. The articles cover a variety of issues concerning the foot and ankle. If you have any recommendations for future articles, email them to rangefootandankle@gmail.com.

You Might Also Enjoy...

Bunions

Bunions are a common, treatable condition. There are a variety of treatments, both surgical and non-surgical.

Foot Fractures

This article goes over the various types of toe and metatarsal fractures and how they can be treated.

Diabetes Awareness Month

November is Diabetes Awareness Month. Diabetes can affect the feet in many ways, including increasing the risk of developing foot wounds.

Hammertoes

Hammertoes are a very common condition affecting the foot. There are both surgical and non-surgical treatment options.