Last revised by Henry Knipe on 24 Sep 2021

The pisiform (os pisiforme) is a small carpal bone on the medial side of the proximal carpal bones row. It is considered a sesamoid bone within the tendon flexor carpi ulnaris

The pisiform sits in an anterior plane to the rest of the carpal bones and articulates with the triquetrum. It has a spherical shape with a slight distolateral long axis. The articular dorsal surface is flat, forming the pisotriquetral joint, whilst the palmar surface is rough and round and provides for muscular attachment. It is the only moving structure of the carpal canal 5.

The ulnar artery sits adjacent to a lateral surface groove of the pisiform. 

The ulnar artery provides vascularity with branches entering both proximal and distal surfaces. Proximal vessels enter inferior to the triquetral facet near the tendon of the flexor carpi ulnaris. Superior and inferior branches run beneath the articular surface and along the palmar cortex respectively. Distal entering vessels run parallel to the palmar cortex and anastomose with the proximal vessels. Superior proximal and distal vessels form an arterial ring deep to the facet. 

See accessory ossicles of the wrist.

Distal avulsion and vertical fracture may occur from a direct blow, especially when the pisiform is tensed from the flexor carpi ulnaris. Mechanism often includes a fall onto an outstretched hand. 

The pisotriquetral joint is a common site of wrist osteoarthritis. 

Often the last carpal bone to ossify, the pisiform has one ossification center that ossifies in the ninth to twelfth year, later in males. 

Derived from the Latin word pisum, pisiform means ‘pea-shaped’. 

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