What is it: The os tibiale externum is an accessory ossicle located on the medial side of foot, proximal to the navicular, within the posterior tibial tendon.
How does it present: Two to twelve percent of the population have this accessory ossicle and many times it does not cause any pain. When it does cause pain, it presents with pain over the medial foot.
Common exam findings: On exam, tenderness over the bony prominence may be appreciated.
Tests and treatment: Foot x-rays may show this ossicle. If there is clinical question as to whether this ossicle is causing the discomfort a bone scan may help with diagnosis. Treatment is usually conservative with padding of the area. Surgical resection may be necessary in recalcitrant cases.