Accessory ossicles are bony structures (normal congenital variant) that separate from adjacent bone and are usually embedded within tendons. More than 40 different types of accessory ossicles have been known to occur in the foot. The most common types of ossicles in the foot include an os trigonum, os peroneum, and accessory navicular. It is important to have a general knowledge of the common accessory ossicles of the foot as they are often found incidentally on X-ray and can be confused with avulsion fractures. Accessory ossicles can also cause painful syndromes that are usually associated with tendinitis of the surrounding tendon.1

Os peroneum is an ossicle located just lateral to the cuboid and is embedded within the peroneus brevis tendon. Several sources of os peroneum pathology can cause pain in the peroneus brevis tendon, including fracture of the ossicle, rupture or tearing of the tendon around the ossicle, and stenosing tenosynovitis. Os peroneum syndrome generally causes symptoms of pain over the lateral cuboid and pain during palpation of the ossicle. Treatment of os peroneum syndrome is the same as for peroneal tendinitis, which includes a period of NSAIDS and immobilization.1,2

Os trigonum is located posterior to the talus and may be a source of pain due to posterior ankle impingement.  Os vesalianum is located proximal to the base of the 5th metatarsal and is often confused with an avulsion fracture of the tuberosity. Os naviculare, or accessory navicular, is a large accessory ossicle adjacent to the medial side of the navicular.1

Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).


  1. Nwawka OK, Hayashi D, Diaz LE, et al. Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology. Insights Imaging. 2013;4:581-593.
  2. Heckman DS, Reddy S, Pedowitz D, Wapner KL, Parekh SG. Operative treatment for peroneal tendon disorders.  J Bone Joint Surg Am. 2008;90:404-418.
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