An Accessory Navicular is an extra bone on the medial side of the navicular that can be symptomatic.
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The accessory navicular is an additional piece of bone on the inside of the foot just on top of the mid-foot close to its top part. The bone is incorporated within the tibialis posterior tendon that attaches into the navicular bone near the top of the mid-foot. The extra bone is also referred to as os navicularum or os tibiale externum. It is hereditary, so is present since birth. There are several different kinds of accessory navicular and the Geist grouping is most often used. This typology separates the accessory navicular into 3 variations:
Type 1 accessory navicular bone:
This is the classical ‘os tibiale externum’ and make up 30% of the cases; it is a 2-3mm sesamoid bone inserted inside the distal portion of the tendon with no connection to the navicular tuberosity and may even be divided from the bone 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 linked to the navicular bone through cartilage material. It could at some point merge to the navicular to create one bone.
Type 3 accessory navicular bone:
Pronounced navicular tuberosity. This might have been a Type 2 that has merged to the navicular
The typical sign associated with an accessory navicular is the prominence on the inside aspect of the mid-foot ( arch ). Due to the additional bone there, this has an effect on how well the mid-foot muscles work and may result in a flat foot. Rigid type footwear, like ski boots, can also be quite painful to use as a result of enlarged prominent bone.
The therapy is directed at the signs and symptoms. If the flatfoot is a concern, then ice, immobilisation and also pain relief drugs may be required at first. Following that, physical rehabilitation and foot orthotic inserts to support the foot are used. When the pain is caused by force from the style of footwear that needs to be worn, then donut type padding is required to get pressure off the uncomfortable region or the shoes might need to be adjusted.
If these non-surgical therapies fail to decrease the symptoms of the accessory navicular or maybe the issue is an ongoing one, then surgery can be a suitable option. This requires removing the accessory bone and fixing the insertion of the posterior tendon so its function is improved.