The pisiform is a sesamoid bone in the flexor carpi ulnaris tendon. Meaning "pea-shaped," this carpal bone is rare to fracture. Often pisiform fractures are with associated injuries - distal radius, hamate, or triquetrum. The mechanism of injury is usually by a direct blow to the palm when the wrist is dorsiflexed pulling the pisiform against the triquetrum.
With the exception of the pisotriquetral ligament and the articular surface with the triquetrum, the pisiform is entirely embedded in the tendon of the flexor carpi ulnaris. It also serves as the proximal origin of the flexor digiti minimi. The vascular supply to the pisiform is via the ulnar artery with its circumferential foramina on the nonarticular surface.
The pisiform can be approached via the palmar approach to Guyon's canal.
Presentation is often delayed when in isolation and it can be overlooked when the pisiform fractures in association with other injuries. Point tenderness can be found on physical examination.
Fractures may be missed on AP and lateral wrist films requiring a external rotation view or carpal tunnel view. When in question, a CT may be required to make the diagnosis.
Generally, cast immobilization is warranted as a first line treatment. The cast should be in ulnar deviation with 30 degrees of flexion. Should the fracture progress to a symptomatic non-union, the pisiform can be excised.
Non-unions are excised.
Loss of grip strength occurs after excision, but the difference between hands is not significant.
Pisotriquetral joint degeneration can also be treated with pisiform excision.