The fabella (Latin for little bean) (or flabella) is a small sesamoid bone found in some mammals embedded in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur. It is named after Vicente Fetalveró y Fabellá. It is an accessory bone, an anatomical variation present in 10% to 30% of humans. Rarely, there are 2 or 3 of these bones (fabella bi- or tripartita). It can be mistaken for a loose body or osteophyte.