Also called the os tibiale externum or os navicularum, accessory navicular is an ossicle, or extra bone, that develops on the inside of the foot, above the arch. It is connected to the posterior tibial tendon and could be fused with the navicular or just a small distance away. As such, it appears to be an extension or an “accessory” of the navicular.
Accessory Navicular Syndrome
If the accessory navicular does not cause any symptoms, the condition might go unnoticed. However, when there is pain involved, it is called the accessory navicular syndrome. This can be triggered by an injury to the foot, such as an ankle sprain, which affects the bone or the posterior tibial tendon. Also an overuse injury, the syndrome could be due to excessive activity, especially when wearing inappropriate footwear that causes constant rubbing against the jutted bone.
More commonly, the first signs of symptoms appear during adolescence, when cartilage is developing into bone. For some, the symptoms only appear in their adulthood, usually after a foot injury of some kind. When this happens, the person would feel pain, redness and swelling on the inside of the foot, above the arch, especially during and after engaging in activity.
The doctor would first examine the foot for swelling, pressing on the bony prominence to access the pain. The way the patient walks would be observed to evaluate the joint motion and muscle strength. It is important to let the doctor know about any previous foot injuries and when the first signs of symptoms appeared. To confirm the diagnosis, an X-ray or MRI may be ordered.
Usually, the first course of treatment to relieve the symptoms would be non-surgical. Even if surgery is needed, conservative treatment would precede the operation for 4-6 months. These are the methods used:
- RICE (Rest, Ice, Compression, Elevation) – To reduce swelling.
- Immobilization – A cast or boot would prevent weight bearing, allowing the foot to heal.
- Orthotic Devices – Custom orthoses provide support for the foot and prevent aggravation.
- Medication – Oral medications may be prescribed to reduce pain and inflammation.
- Physical Therapy – Exercises and treatments such as Ultrasound and electrical stimulation help to reduce inflammation and strengthen the muscles.
Depending on the symptoms and condition, the surgery opted for may be the simple excision or the Kidner procedure.
- Simple excision – The accessory navicular is removed along with the bone so that there is no more bony prominence and the symptoms can be relieved. The ligament is then reattached to the navicular.
- Kidner procedure – Similar to the simple excision, the bony prominence is removed in the Kidner procedure. Additionally, the posterior tibial tendon is split and relocated to the navicular.