pisiform

The pisiform is a small, pea-shaped bone in the proximal row of the carpus (wrist). It is a sesamoid bone embedded within the tendon of the flexor carpi ulnaris and lies on the palmar surface of the wrist, near the little finger. The pisiform articulates with the triquetrum through a small facet, forming a limited joint, but it has no direct articulation with other carpal bones. It is connected and stabilized by ligaments and the FCU tendon.

Developmentally, the pisiform ossifies from a single center during childhood. It remains a distinct bone within the wrist and is held in place largely by the surrounding tendon and ligamentous attachments. Its surface features include a small articular facet for the triquetrum; the majority of its surface provides attachments for soft tissues and serves as the pulley for the FCU tendon.

Functionally, the pisiform serves as a sesamoid within the flexor carpi ulnaris tendon, increasing the tendon’s mechanical advantage and acting as a pulley. This arrangement redirects tendinous force during wrist flexion and ulnar deviation, enhancing flexor efficiency and reducing wear on the tendon.

Clinical significance, variants, and injuries: Fractures of the pisiform are uncommon but can occur after direct trauma or forced wrist hyperflexion. Diagnosis is typically via radiographs; a bipartite pisiform—a normal anatomical variant with two ossification centers—can mimic fracture. Treatment ranges from immobilization for simple fractures to surgical excision in persistent pain or nonunion, with generally preserved wrist function after removal.

Anatomic variation: The bipartite pisiform occurs in a minority of individuals and may be mistaken for a displaced fracture on imaging.