The Accessory Navicular

The accessory navicular is a supplementary piece of bone on the medial side of the foot just above the mid-foot near its highest point. The bone is integrated within the tibialis posterior tendon which attaches into the navicular bone at the top of the arch. The additional bone can also be referred to as os navicularum or os tibiale externum. This is genetic, so is existing from birth. There are several different types of accessory navicular and the Geist typology is mostly used. This classification divides the accessory navicular into 3 varieties:

Type 1 accessory navicular bone:
This is the classical ‘os tibiale externum’ making up to 30% of the cases; it's a 2-3mm sesamoid bone embedded within the distal portion of the tendon without any link to the navicular tuberosity and may even be separated from it by up to 5mm
Type 2 accessory navicular bone:
This type makes up about 55% of the accessory navicular bones; it is triangular or heart-shaped and attached to the navicular bone via cartilage material. It may well at some point merge to the navicular to form one bone.
Type 3 accessory navicular bone:
Prominent navicular tuberosity. This may have been a Type 2 that's joined to the navicular

The common sign associated with an accessory navicular is the prominence on the medial side of the mid-foot ( arch ). Due to the additional bone there, this impacts how well the mid-foot muscles perform and can lead to a painful foot. Rigid type shoes, such a ski boots, will also be very uncomfortable to wear as a result of enlarged pronounced bone.

The therapy is usually geared towards the symptoms. When the flatfoot is a concern, then ice, immobilisation and also pain relief medicine may be required at first. Following that, physical therapy and foot orthotic devices to aid the feet are used. When the soreness is because of force from the style of footwear that needs to be used, then donut type padding is required to get load off the sore spot or the footwear might need to be adjusted.

If these non-surgical treatment options are not able to reduce the symptoms of the accessory navicular or the problem is an ongoing one, then surgical treatment can be a suitable alternative. This requires removing the accessory bone and restoring the insertion of the posterior tendon so its function is enhanced.