A symptomatic sesamoid bone in the popliteus muscle (cyamella).

Sesamoid bones of the popliteus muscle, also called cyamellae, are common in primates but rare in humans. They reside as accessory bones in the tendon itself or in the intersection between tendon and bone. They should be clearly distinguished from osteochondral flakes, periosseuos calcifications, osteophytes and the fabella, a common sesamoid bone of the knee. In this case, we report a 25-year-old male with posterior lateral knee pain related to the popliteus tendon where a corresponding cyamella could be demonstrated on X-rays and MRI scans. The clinical findings may be related to the cyamella. Diagnosis and treatment of this rare pathology are discussed.