Os sesamoideum, also known as the sesamoid bones, are small bones that are located near the joints. These bones are found throughout the body, especially in the hands, feet, and knees. The term sesamoid bone is derived from the word "sesame seed," as these bones are roughly the same size and shape as these seeds. Other synonyms for os sesamoideum include accessory bones, fabella, and patellar accessory bones. These alternate names are often used in medical terminology to describe the small, round bones that are present within tendons or ligaments, protecting them from wear and tear. Regardless of the name used, these bones play an important role in facilitating joint movement and reducing friction within the body.