The fabella (Latin for little bean) 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 a variant of normal anatomy and present in humans in 10% to 30% of individuals. Rarely, there are 2 or 3 of these bones (fabella bi- or tripartita). It is often mistaken for a loose body or osteophyte.

References

• Duncan W, Dahm D (2003). "Clinical anatomy of the fabella". Clin Anat 16 (5): 448–9.