The Accessory Navicular

The accessory navicular is an extra piece of bone on the inside of the foot just above the mid-foot ( arch ) in close proximity to its top point. The bone is enclosed within the tibialis posterior tendon that inserts to the navicular bone towards the top of the mid-foot. The additional bone is also referred to as os navicularum or os tibiale externum. It is congenital, so is present from birth. There are various types of accessory navicular and the Geist classification is frequently used. This categorization divides the accessory navicular into 3 variations:

Type 1 accessory navicular bone:
This is the typical ‘os tibiale externum’ making up 30% of the occurrences; it’s a 2-3mm sesamoid bone embedded inside the distal portion of the tendon with no connection to the navicular tuberosity and may be divided from the bone by up to 5mm

Type 2 accessory navicular bone:
This type makes up about 55% of the extra navicular bones; it’s triangular or heart-shaped and linked to the navicular bone via cartilage material. It may well eventually merge to the navicular to create one bone.

Type 3 accessory navicular bone:
Pronounced navicular tuberosity. This might have been a Type 2 that’s merged to the navicular

The common symptom associated with an accessory navicular is the enlargement on the inside side of the arch. Because of the extra bone there, this affects how well the mid-foot muscles do the job and can lead to a painful foot. Rigid type shoes, such a ice skates, may also be very uncomfortable to use because of the enlarged pronounced bone.

The treatment is usually geared towards the signs and symptoms. If the flatfoot is a concern, then ice, immobilisation and pain relief medication may be required initially. Following that, physical therapy and foot orthotic inserts to aid the foot are used. If the soreness is due to pressure from the type of footwear that must be worn, then doughnut type padding is used to get load off the sore region or the footwear may need to be modified.

If these non-surgical treatment options fail to minimize the symptoms of the accessory navicular or the issue is a continuing one, then surgical procedures might be an appropriate option. This involves taking out the accessory bone and restoring the insertion of the tibialis posterior tendon so its function is improved upon.