The pisiform bone is a small sesamoid bone found in the proximal row of the wrist (carpus). It situated where the ulna joins the wrist, within the tendon of the flexor carpi ulnaris muscle.[1]:199,205

It only has one side that acts as a joint, articulating with the triquetral bone. It is on a plane anterior to the other carpal bones and is spheroidal in form.

The pisiform bone has four surfaces:

  The dorsal surface is smooth and oval, and articulates with the triquetral: this facet approaches the superior, but not the inferior border of the bone.
  The palmar surface is rounded and rough, and gives attachment to the transverse carpal ligament, the flexor carpi ulnaris and the abductor digiti quinti.
  The lateral and medial surfaces are also rough, the former being concave, the latter usually convex.

Function

Unlike the other carpal bones, the pisiform is not involved in movement of the wrist.[2] :5