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An example of a Type B sesamoid bone is the sesamoid of the peroneus (fibularis) longus tendon. Type B sesamoid bones overlie a bony prominence and are separated by an underlying bursa. Common examples of this type include the hallucis and pollicis sesamoids along with the patella, allowing for increased leverage. Type A sesamoid bones are adjacent to a joint, becoming a part of the joint capsule. Together a sesamoid bone and its relation to other tendons form a joint. Bony surfaces are surrounded by cartilage and incorporated within the cavity, forming the synovium. īased on their positioning and attachment, sesamoid bones can be divided into two broad categories, type A and B. Injuries to the patella greatly reduce its leverage and extensor capabilities these injuries commonly result from trauma and increased tension. This unique mechanism allows for the knee's range of motion and increased weight-bearing activities. For example, the patella increases joint leverage and contributes to our knee's extensor properties. The body contains many sesamoid bones, often offering an added strength advantage to t­­he muscles and supporting tendon stability. While most sesamoid bones are small, these bones play a critical role in our body in leverage, decreasing overall friction and allowing for our body's unique biomechanics and distinct range of motion. Sesamoid bones relieve tension within muscles and tendons, allowing for increased weight-bearing and tolerance by redistributing forces throughout a muscle or tendon, thereby protecting them from significant strain and injury. These bones are often formed in response to added strain to muscles and tendons but can also be normal variants, most commonly present in the hand. There are many sesamoid bones in a person, with up to 42 reportedly found in an individual.

Sesamoid bones are most commonly located in the foot, hand, and wrist the largest and most well-known is the patella.

The word "sesamoid" derives from the Arabic word 'sesamum' translating to sesame, given that many sesamoid bones are small. Unlike standard bones, which connect via joints, sesamoid bones connect to muscles via tendons. A sesamoid bone is a small bone commonly found embedded within a muscle or tendon near joint surfaces, existing as focal areas of ossification and functioning as a pulley to alleviate stress on that particular muscle or tendon.