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Other Terms: Pisiform bone, Os pisiforme
This is the smallest of the carpal bones. Unlike all the other carpal bones that have multiple articular surfaces, this bone forms a single articulation. It is spheroidal, although it can be quite variable in shape. It sits on a plane palmar to all the other carpal bones. Its dorsal surface forms a flat facet. All the other surfaces are rough with the palmar surface providing attachment for the flexor retinaculum, flexor carpi ulnaris, and abductor digiti minimi. The lateral surface is usually marked by a shallow groove for the ulnar artery. The pisiform bone is palpable on the palmar surface about three centimeters distal to the head of the ulna.
Pisiform is derived from the Latin pisum meaning pea and forma meaning shape. This small round bone resembles a pea in size and shape. Historically the bone has had many synonyms, they are the subrotundum, obiculare, and lentiforme.
The pisiform articulates with one bone: the triquetral. The dorsal surface of the bone forms a smooth oval facet for articulation with the ventral surface of the triquetral bone.
The pisiform bone ossifies from a single center. It is the last carpal bone to ossify arising in the ninth to tenth year in females and during the twelfth year in males.