Os Peroneum

The os peroneum is an accessory ossicle found within the peroneus longus tendon near the calcaneocuboid joint. The ossicle may be single-part or multipartite (bipartite shown here). It is found in about 10% of radiographs, but is thought to be always present in a cartilaginous or fibrocartilaginous stage.

While most often an incidental finding, the os peroneum can be associated with pain. The os peroneum syndrome presents with lateral pain, tenderness and swelling along the course of the peroneus longus tendon. There is also lateral pain with plantar flexion of the foot against resistance.

Os peroneum syndrome can be initiated by:

• Os peroneum fracture
• Hypertrophic healing of an os peroneum fracture
• Diastasis of a multipartite os peroneum
• Attrition or tear of the peroneus longus tendon
• Enlarged peroneal tubercle of the calcaneus

References

• Mellado JM, Ramos A, Salvadó E, Camins A, Danús M, Saurí A. Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. Eur Radiol. 2003 Dec;13 Suppl 6:L164-77.
• Pierson JL, Inglis AE. Stenosing tenosynovitis of the peroneus longus tendon associated with hypertrophy of the peroneal tubercle and an os peroneum. A case report. J Bone Joint Surg Am. 1992 Mar;74(3):440-2.