The pisiform is a sesamoid bone within the flexor carpi ulnaris tendon. It is positioned immediately volar to the triquetrum and is the palpable bony prominence at the base of the hypothenar eminence. Injuries usually result from a fall directed on the hypothenar eminence. There will be localized tenderness on the pisiform itself. If the wrist is flexed, the pisiform can be grasped and ballotted between the examiner's fingers. This should elicit pain. Because the pisiform and hook of the hamate form the bony walls of Guyon's canal that contains the ulnar nerve and artery, it is important to exclude injury to them. Radiographs in partial supination or the carpal tunnel view are the optimal views because they remove the overlap with the triquetrum present on standard views (see Fig 262-11). Multiple ossification centers in the pisiform may be confused with a fracture; however, these will have smoother margins and lack the perfect jigsaw puzzle fit seen with fracture fragments. Pisiform fractures are treated either in a compression dressing or a splint in 30 degrees of flexion and ulnar deviation that relaxes the tension from the flexor carpi ulnaris. These fractures have an excellent prognosis.
FIG. 262-11. Pisiform fracture PA view with a thin lucency in the center of the bone (arrow). (With permission from Chin HW, Visotsky J: Wrist fractures. Em Med Clin North Am 11:3, 1993.)
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