The os tibiale externum is associated with the navicular bone on the inside aspect of the foot near the arch. The navicular bone can sometimes have an accessory bone with a secondary ossification (growth)center. This accessory bone would can be called many names including accessory navicular, os tibiale externum, navicular secundum, prehallux, bifurcate navicular, accessory tarsal scaphoid, extra scaphoid, and divided navicular. The condition exists from birth and during development. This bone may be fused (connected)to the remaining navicular body, or remain as a seperate or partially attached bone. A “true” os tibiale externum is thought to be an actual sesamoid bone and remains unattached.
Symptoms usually deal with pain and blisters or an ulcer due to shoe irritation on the inside aspect of the foot. Looking at the foot there is usually a bump or prominence associated with the blister or area of friction. The foot can become very flat and this bump may actually touch the ground in some individuals.
Causes are not clearly understood, although like most foot structural problems are strongly associated with heredity.
Prevention is aimed at treating the biomechanical problems associated with having an os tibiale externum. Since there is a strong genetic predisposition for the structure of your foot, there is not a lot we can do to change this factor. Proper shoe wear at all times may be the best prevention. Sometimes extra pressure can be relieved by padding over the bony prominence. If the area is irritated with redness, swelling, and pain some ice and anti-inflammatory medications may be helpful. The best prevention may be to get advice from your podiatrist.
Podiatric Care usually begins with x-rays to evaluate the structure of your foot and to rule out other injuries. Treatment may include using anti-inflammatory oral medications or an injection of medication and local anesthetic to reduce this swelling. The podiatrist may see you to take care of any callouses that develop due to the os tibiale externum. They may advise you on different shoewear or prescribe a custom made orthotic to try and control the foot structure especially if you have excessive pronation. Your podiatric physician may also recommend a surgical procedure to actually fix the structural problem of your foot.
Surgery to correct your foot structure may be the best option for you and can be preventative for ulcers. Surgery can greatly vary depending upon age, bone quality, expectations, activity level, and surgeons preference. Part of the navicular may be simply reshaped or removed to help relive the pain and pressure. Others may have soft tissue tendon transfers to realign the structure of the foot. There are too many surgical possibilities to discuss each in detail in this section. Your podiatrist will discuss the differences, risks and benefits of each. Even with surgical operation you may require an orthotic for long term control of your foot. Your podiatrist will give you advise on this.
Post-operative Care and Risks of surgery depends greatly on the procedure. You may need a cast to protect you for a short time. Sometimes a soft bandage with a post-operative shoe is allowed. You should expect some pain following surgery as well as swelling. Especially for the first 48 hours you should keep your leg elevated and occasional ice placed over the area of surgery (about 20 minutes per hour). Surgical cuts are made through the skin so a scar is expected. If you are a keloid former, let your surgeon know. Surgical cuts are not only made through skin, but through other layers of tissue as well, a scar may form within your foot and lead to adhesions. For many flatfoot type of surgeries you will be required to keep all weight off of your foot for several weeks. You may use crutches, a walker, or wheelchair to help you keep weight off of this foot. Healing time is typically 6-8 weeks or longer for all bone cuts. This is influenced by many factors including your nutrition, circulation, and other medical conditions. If you are a smoker you can expect to take longer to heal. If your bone heals real slow it may be a delayed union, or if not at all a non-union. If you are required to keep pressure off of your foot your leg muscles are not being used as they were before surgery. This allows for slower movement of the blood through the leg vessels. Occasionally this can lead to a blood clot in the leg which can become life threatening. Hip and knee flexion and extension exercises as well as wiggling your toes gently can help prevent this from occurring. If you have a history of blood clots you should let your surgeon know.