Pisiform Bone

The pisiform bone is a sesamoid bone spherical shape, pea-shaped bone in the proximal carpal row, located on the anterior plane of the volar and ulnar aspect with a slight distolateral long axis, or anteromedial side of the wrist joint in the proximal row of carpal bones by articulating with the triquetrum where the ulna joins the wrist. The pisiform bone also spelled pisiform (from the Latin piriformis, pea-shaped it develops in a tendon), is a small knobbly, one of eight, and smallest sesamoid bones that are found in the wrist. It forms the ulnar border of the carpal tunnel, one side that acts as a joint for articulating with the triquetral bone, and is enveloped in the flexor carpi ulnaris tendon, and can be easily palpated from the exterior.

It is the only moving structure of the carpal canal. The pisiform bone has four surfaces:

1. The dorsal surface is smooth, oval, flat, forming the pisotriquetral joint and articulates with the triquetral with this facet approaches the superior, but not the inferior border of the bone.
2. The palmar surface is rounded, rough, and provides for muscular attachment to the transverse carpal ligament, the flexor carpi ulnaris, and the abductor digiti quinti.
3. The lateral surface is rough and concave in shape.
4. The medial surface‘ is rough and usually convex in shape.

The pisiform bone, along with the hamulus of the hamate, forms the medial boundary of the carpal tunnel because the pisiform body acts as one of the four attachments places of the flexor retinaculum. It also works as an attachment site for tendons of the abductor digit minimi and for the flexor carpi ulnaris tendon from where form bone. The pisiform is the only carpal bone in which insertions and attachments for the abductor digiti minimi and the flexor carpi ulnaris muscle. It is universally known that due to the pisiform’s large range of movement along its articulation surface with the triquetral bone (about 1 cm of movement is allowed), contraction of the flexor carpi ulnaris is urgent for the pisiform to remain stable for the abductor digiti minimi to function strongly.

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