Presented at the 2012 AAPM Annual Meeting « Back

Painless Knee Clicking Due to a Cyamella (Popliteus Muscle Sesamoid Bone): A Case Report

Jason Siefferman, MD, jsiefferman@gmail.com¹, Parag Sheth, MD¹, (1) Mount Sinai School of Medicine, New York, New York

Case: We report the case of a 44-year-old female dancer who presented with five weeks of painless knee clicking. At the time, she had been training for a routine with repetitive jumping, pivoting and twisting. Initial swelling and pain resolved, however, clicking persisted. Physical exam revealed no effusion, tenderness, instability, or other finding suggestive of degeneration, meniscal or ligamentous injury. Clicking localized to the posterior lateral knee and only occurred at the end range of active extension. Ultrasound examination revealed popliteus tendon edema and radiographs of the knee revealed a cyamella, a rare sesamoid bone within the popliteus muscle. Assessment: Knee clicking due to popliteus tendon laxity and cyamella hypermobility. Discussion: Sesamoid bones facilitate the physiological motion of tendons by diminishing friction, modifying pressure, and altering the direction of pull. Cyamellas are usually found near the musculotendinous junction of the popliteus muscle, and only four cases have been reported in humans. Of these, all were men, and only two were pathologic. Both cases, like ours, presented with lateral knee pain and swelling which resolved with conservative management. Based on the location and inciting activity of clicking in our patient, it was most likely attributable to popliteus tendon laxity. Laxity would allow the cyamella to sublux and reduce around a nearby structure causing clicking with extension. As there was no pain or instability, no treatment was indicated. Conclusion: Cyamellas are very rare in humans and may be a source of lateral knee pain, swelling or clicking.

Funding: None