Sesamoid is the medical term that describes this condition
Sesamoid is a small nodular bone that is firmly fixed in a tendon or muscle. Sesamoid forms as a result of pressure, or it can form normally on its own. Sesamoids are present in many joints in the body such as in the foot and knee. Sesamoids functions like pulleys for tendons. They enhance the ability of the tendons to transmit muscle forces by creating a smooth surface for the tendons to slide over.