Sesamoid bone

Sesamoid bones can be found on joints throughout the human body, including: • In the knee—the patella (within the quadriceps tendon). This is the largest sesamoid bone. • In the wrist—The pisiform of the wrist is a sesamoid bone (within the tendon of flexor carpi ulnaris). It begins to ossify in children ages 9–12. • In the foot—the first metatarsal bone usually has two sesamoid bones at its connection to the big toe (both within the tendon of flexor hallucis brevis). One is found on the lateral side of the first metatarsal while the other is found on the medial side. In some people, only a single sesamoid is found on the first metatarsal bone. ==Common variants==

of the foot by dorsoplantar view, with most common accessory and sesamoid bones. • One or both of the sesamoid bones under the first metatarsophalangeal joint (of the great toe) can be multipartite – in two or three parts (mostly bipartite – in two parts). • The fabella 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. The fabella can also be mutipartite or bipartite. • The cyamella is a small sesamoid bone embedded in the tendon of the popliteus muscle. It is a variant of normal anatomy. It is rarely seen in humans, but has been described more often in other primates and certain other animals. File:Accessory and sesamoid bones of the foot - lateral projection.jpg|Lateral view. File:Pie metatarso-falanges.JPG|Bipartite medial sesamoid bone under the first metatarsophalangeal joint of the great toe of the left foot of an adult woman. ==Clinical significance==

• A common foot ailment in dancers is sesamoiditis (an inflammation of the sesamoid bones under the first metatarsophalangeal joint of the big toe). This is a form of tendinitis which results from the tendons surrounding the sesamoid becoming inflamed or irritated. ==Other animals==

In equine anatomy, the term sesamoid bone usually refers to the two sesamoid bones found at the back of the fetlock or metacarpophalangeal and metatarsophalangeal joints in both hindlimbs and forelimbs. Strictly these should be termed the proximal sesamoid bones whereas the navicular bone should be referred to as the distal sesamoid bone. The patella is also a form of sesamoid bone in the horse. Although many carnivores have radial sesamoid bones, the giant panda and red panda independently evolved to have an enlarged radial sesamoid bone. This evolution has caused the two species to diverge from other carnivores. In these two panda species, DYNC2H1 gene and PCNT gene have been identified as possible causes for the pseudo-thumb development. Recently, the enlarged radial sesamoid bone of cotton rats has been studied. Their enlarged radial sesamoid bone and that of the giant panda have a similar morphology and size relative to the rest of the hand. The forepaws of moles also possess a prepollex consisting of an enlarged, sickle-shaped sesamoid. ==See also==