Cyamella

Lateral conventional radiograph of the knee and sagittal, coronal, and axial T1-WI of the knee show an ossicle within the popliteus muscle. Case Courtesy of Thomas Martin, MD.

The cyamella, also known as the popliteal fabella or the fabella distalis, is an uncommon sesamoid bone of the knee that is typically found in the popliteus tendon, but can also be seen at the myotendinous junction and even in the muscle. On radiographs, it is seen as a small, ossified structure, that is typically seen in the popliteal groove, but can be seen anywhere along the course of the popliteus tendon.

The cyamella is rarely seen, and even more rarely associated with pathology. A case of painful dislocation has been reported.

It is more common in some nonhuman primates, as well as in dogs and kangaroos.

References

• Le Minor JM. Brief communication: the popliteal sesamoid bone (cyamella) in primates. Am J Phys Anthropol. 1992 Jan;87(1):107-10.
• Mishra AK, Jurist KA. Symptomatic cyamella. Arthroscopy. 1996 Jun;12(3):327-9.
• Munk PL, Althathlol A, Rashid F, Malfair D. MR features of a giant cyamella in a patient with osteoarthritis: presentation, diagnosis and discussion. Skeletal Radiol. 2009 Jan;38(1):69, 91-2.