This syndrome is also referred to as os tibial naviculare or os tibial externum. As stated above, this condition quite often does not cause any pain. But if the posterior tibial tendon (the extra bone attaches to this tendon in the foot) or the accessory navicular bone itself were to get aggravated, then there would be pain.
Like all painful conditions, ANS has a root cause. The cause could be the accessory navicular bone itself producing irritation from shoes or too much activity. Often, however, it is related to injury of one of the structures that attach to the navicular bone. Structures that attach to the navicular bone include abductor hallucis muscle, plantar calcaneonavicular ligament (spring ligament) parts of the deltoid ligament, posterior tibial tendon.
Possible symptoms of accessory navicular syndrome include redness or swelling in the area of the accessory navicular, and pain that is present around the middle of the foot around the arch. Discomfort is most often present following periods of exercise or prolonged walking or standing. The bone may be somewhat visible on the inside of the foot above the arch. Most symptoms of accessory navicular syndrome first appear in childhood around the time of adolescence as the bones are still growing and developing. For some with an accessory navicular, though, symptoms may not appear until entering adulthood.
Plain x-rays are used to determine the size of the accessory navicular. There are three main types of accessory navicular bones: a small bone embedded within the nearby posterior tibial tendon; a triangular shaped bone connected to the navicular by thick cartilage; and a large prominent navicular tuberosity thought to represent an accessory navicular that has fused to the navicular. If the status of the posterior tibial tendon needs to be assessed or if other problems are suspected, (ex. Navicular stress fracture) it may be necessary to perform an MRI. Although this is not considered routine, an MRI may be helpful in identifying the degree of irritation. An MRI would demonstrate fluid or edema that may accumulate in the bone as a result of the irritation.
Non Surgical Treatment
Many individuals with symptomatic accessory naviculars can be managed successfully without surgery. Standard non-surgical treatment includes shoes that are soft around the inside of the ankle can allow for any excess prominence of bone. Therefore, it is recommended that either shoes with plenty of padding and space in the ankle area are purchased, or pre-owned shoes can be modified by a shoemaker to create extra space in this area. For example, many patients will get their ski boots expanded in the area around the prominence, minimizing irritation. In addition, a shoe with a stiff sole will help disperse force away from the arch of the foot during walking, thereby minimizing the force on the posterior tibial tendon. An off-the-shelf arch support may help decrease the stress applied by the posterior tibial tendon. If necessary, an ankle brace applied to provide more substantial support to the arch may be successful where a simple arch support fails.
If all nonsurgical measures fail and the fragment continues to be painful, surgery may be recommended. The most common procedure used to treat the symptomatic accessory navicular is the Kidner procedure. A small incision is made in the instep of the foot over the accessory navicular. The accessory navicular is then detached from the posterior tibial tendon and removed from the foot. The posterior tibial tendon is reattached to the remaining normal navicular. Following the procedure, the skin incision is closed with stitches, and a bulky bandage and splint are applied to the foot and ankle. You may need to use crutches for several days after surgery. Your stitches will be removed in 10 to 14 days (unless they are the absorbable type, which will not need to be taken out). You should be safe to be released to full activity in about six weeks.