The accessory navicular is a supplementary bit of bone on the inside of the foot just on top of the mid-foot in the vicinity of its highest part. The bone is included within the tibialis posterior tendon that attaches to the navicular bone towards the top of the mid-foot ( arch ). The additional bone can also be known as the os navicularum or os tibiale externum. This is genetic, so is existing since birth. There are a few different kinds of accessory navicular and the Geist classification is most typically used. This classification divides the accessory navicular into 3 varieties:

Type 1 accessory navicular bone:
This is the classical ‘os tibiale externum’ and make up 30% of the occurrences; it is a 2-3mm sesamoid bone embedded inside the distal area of the tendon with no link to the navicular tuberosity and could be separated from it by up to 5mm

Type 2 accessory navicular bone:
This type makes up 55% of the accessory navicular bones; it’s triangular or heart-shaped and connected to the navicular bone through cartilage. It may well eventually join to the navicular to form one bone.

Type 3 accessory navicular bone:
Prominent navicular tuberosity. This could have been a Type 2 that has fused to the navicular

The typical symptom associated with an accessory navicular is the enlargement on the inside side of the mid-foot ( arch ). Because of the additional bone there, this impacts how well the mid-foot muscles do the job and may lead to a painful foot. Inflexible type shoes, like ice skates, may also be very uncomfortable to use because of the enlarged pronounced bone.

The treatment is geared towards the signs and symptoms. When the flatfoot is an issue, then ice, immobilisation and also pain relief medication may be required to start with. Following that, physical therapy and foot orthotic inserts to aid the foot are used. When the soreness is a result of pressure from the type of shoes which needs to be used, then donut type padding is required to get pressure off the painful region or the shoes might need to be modified.

If these non-surgical therapies fail to reduce the symptoms of the accessory navicular or maybe the issue is an ongoing one, then surgery may be a suitable option. This requires removing the accessory bone and restoring the insertion of the posterior tendon so its function is improved.