Accessory navicular bone
|Accessory navicular bone|
X-ray of the foot showing an accessory navicular bone
|Latin||Os tibiale, os tibiale externum or naviculare secundarium|
|Anatomical terms of bone|
An accessory navicular bone is an accessory bone of the foot that occasionally develops abnormally in front of the ankle towards the inside of the foot. This bone may be present in approximately 2-21% of the general population and is usually asymptomatic. When it is symptomatic, surgery may be necessary.
Surgery can be performed at any age because it does not alter any other bones.
The Geist classification divides the accessory navicular bones into three types.
- Type 1: An os tibiale externum is a 2–3 mm sesamoid bone in the distal posterior tibialis tendon. Usually asymptomatic.
- Type 2: Triangular or heart-shaped ossicle measuring up to 12 mm, which represents a secondary ossification center connected to the navicular tuberosity by a 1–2 mm layer of fibrocartilage or hyaline cartilage. Portions of the posterior tibialis tendon sometimes insert onto the accessory ossicle, which can cause dysfunction, and therefore, symptoms.
- Type 3: A cornuate navicular bone represents an enlarged navicular tuberosity, which may represent a fused Type 2 accessory bone. Occasionally symptomatic due to bunion formation.
Aside from surgery, there are a few options for handling an accessory navicular bone that has become symptomatic. This includes immobilization, icing, medicating, physical therapy, and orthotic devices. Immobilizing involves placing the foot and ankle in a cast or removable walking boot. This alleviates stressors on the foot and can decrease inflammation. Icing will help reduce swelling and inflammation. Medication involves usage of nonsteroidal anti-inflammatory drugs, or steroids (taken orally or injected) to decrease inflammation. Physical therapy can be prescribed in order to strengthen the muscles and help decrease inflammation. Physical therapy can also help prevent the symptoms from returning. Orthotic devices (arch support devices that fit in a shoe) can help prevent future symptoms. Occasionally, the orthotic device will dig into the edge of the accessory navicular and cause discomfort. For this reason, the orthotic devices made for the patient should be carefully constructed.
- Miller TT, Staron RB, Feldman F, Parisien M, Glucksman WJ, Gandolfo LH (June 1995). "The symptomatic accessory tarsal navicular bone: assessment with MR imaging". Radiology. 195 (3): 849–853. PMID 7754020. doi:10.1148/radiology.195.3.7754020.
- Golano, P; Fariñas, O; Sáenz, I (March 2004). "The anatomy of the navicular and periarticular structures.". Foot and ankle clinics. 9 (1): 1–23. PMID 15062212. doi:10.1016/S1083-7515(03)00155-4.