An accessory navicular bone is an

accessory bone An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography. Wrist and hand ...

of the foot that occasionally develops abnormally in front of the

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular ...

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. Accessory navicular bone may cause a continuous stretch and stress on the tibialis posterior tendon which can progress to chronic disabling pain and may cause tendon rupture or secondary flat foot deformity; when this occurs this condition is commonly known as accessory navicular syndrome. Other conditions which closely mimic the symptoms of an accessory navicular bone include

plantar fasciitis Plantar fasciitis or plantar heel pain (PHP) is a disorder of the plantar fascia, which is the connective tissue which supports the arch of the foot. It results in pain in the heel and bottom of the foot that is usually most severe with the ...

, bunions and

heel spur A calcaneal spur (also known as a heel spur) is a bony outgrowth from the calcaneal tuberosity (heel bone). Calcaneal spurs are typically detected by x-ray examination. It is a form of exostosis. When a foot is exposed to constant stress, calc ...

Classification

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.

Diagnosis

To diagnose accessory navicular syndrome, the foot and ankle surgeon will ask about symptoms and examine the foot, looking for skin irritation or swelling. The doctor may press on the bony prominence to assess the area for discomfort. Foot structure, muscle strength, joint motion and the way the patient walks may also be evaluated. X-rays are usually ordered to confirm the diagnosis. If there is ongoing pain or inflammation, an MRI or other advanced imaging tests may be used to further evaluate the condition.

Treatment

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 A controlled ankle motion walking boot, or CAM boot, also sometimes called a below knee walking boot or moon boot, is an orthopedic device prescribed for the treatment and stabilization of severe sprains, fractures, and tendon or ligament A ...

. 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 Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...

, or

steroids A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and ...

(taken orally or injected) to decrease

inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

Physical therapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patie ...

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.

Radiological images

File:Os tibiale externum Typen 1 - 3 nach Geist - Roe.jpg, From left to right: Type 1, 2 and 3 File:Os-naviculare-accesorium.jpg, Lateral projection of type 2 File: Accessory Navicular 01.jpg, Type 2 File:Os naviculare cornutum - Roe 001.jpg, Cornuate navicular bone File:Os naviculare cornutum - Roe 002.jpg, Cornuate navicular bone File:Os naviculare cornutum - Roe Ausschnitt 001.jpg, Cornuate navicular bone File:Accessory and cornuate navicular bone on dorsoplantar X-ray - annotated.jpg, Type 2 on one foot (dark arrow) and type 3 on the other (white arrow)

References

External links

* {{Commons category-inline
Wheeless' Textbook of Orthopaedics
Skeletal disorders Accessory bone