O is for Os tibiale externum

September 7, 2013

Os tibiale externum is another name for an accessory navicular, an extra ossicle of bone attached to the tibia, usually where the poeterior tibial muscle attaches.

Os tibiale externum

“Os tibiale externum” refers to an accessory bone or an additional bone that can sometimes be found in the foot. Specifically, it is an accessory bone located on the lateral (outer) side of the foot near the navicular bone. It is also known as the accessory navicular bone or the os naviculare accessorium.

The tibialis posterior tendon attaches to the navicular bone, and in some individuals, an extra bone develops within this tendon. This accessory bone is the os tibiale externum or accessory navicular bone. It is a congenital anomaly, meaning it is present from birth, although it may not cause any symptoms or be noticed until later in life.

The presence of an os tibiale externum can potentially cause issues if it is large or if the attached tendon becomes inflamed or irritated. It can lead to a condition called accessory navicular syndrome, which is characterized by pain, tenderness, swelling, and sometimes a visible prominence on the inner side of the foot. The symptoms may worsen with activity or prolonged standing.

Treatment for accessory navicular syndrome usually involves conservative measures such as rest, immobilization, orthotic devices, and anti-inflammatory medications to reduce pain and inflammation. In cases where conservative treatment does not provide relief, surgical removal of the accessory bone or correction of the associated tendon may be considered.


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