Introduction: Accessory ossicles are well-corticated bony structures found close to bones or a joint. They may be unilateral or bilateral. The os tibiale externum is also known as accessory navicular bone, os naviculare secundarium, accessory (tarsal) scaphoid, or prehallux. It is found within the tibialis posterior tendon near its insertion on the navicular bone. The os peroneum is a small sesamoid bone located within the peroneus longus tendon, adjacent to the cuboid. We present a case series of five patients with accessory ossicles of the foot to demonstrate pitfalls in the diagnosis of foot and ankle pain.
Case report: The case series includes four patients with os tibiale externum and one patient with os peroneum. Only one patient had symptoms related to os tibiale externum. The accessory ossicle in the rest of the cases was discovered incidentally after trauma to the ankle or foot. The symptomatic os tibiale externum was managed conservatively with analgesics and shoe inserts for medial arch support.
Conclusion: Accessory ossicles are considered developmental anomalies and they originate from ossification centers that have failed to fuse with the main bone. Clinical suspicion and awareness about the existence of the commonly occurring accessory ossicles of the foot and ankle are necessary. They can be a confounding factor in the diagnosis of foot and ankle pain. Failure to notice their presence might result in a misdiagnosis and unnecessary immobilization or surgery for the patients.
Keywords: Accessory ossicles; os peroneum; os tibiale externum.
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