Presentation
Right foot pain - distal to medial malleolus. No history of trauma or sprain. Query tendinitis.
Patient Data
There is an os tibiale externum on the right, also known as accessory navicular or os naviculare accessorium; an accessory ossicle adjacent to the medial side of the navicular bone.
The patient was significantly tender over the accessory navicular bone.
Case Discussion
There are appearances in keeping with tibialis posterior insertional tendinopathy, with marked associated bony irregularity and calcification of the accessory navicular bone or tibialis enthesopathy.
The tibialis posterior tendon often inserts with a broad attachment into the ossicle.
Most cases of os tibiale externum are asymptomatic but in a small proportion it may cause painful tendinopathy due to traction between the ossicle and the navicular bone.
Ultrasound-guided steroid injection could be considered if more conservative treatment is not successful.
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