AP, lateral, and oblique views of the wrist
Click an image for a more detailed view.
AP, lateral, and oblique views of the wrist
Click an image for a more detailed view.
While fractures of the hamate usually occur through the hook or body
of the bone, one may also encounter the type of fracture seen in this patient.
Some authors have concluded that this injury represents a coronal fracture
through the dorsal aspect of the hamate that occurs when the fourth and/or
fifth metacarpal dislocates or subluxes posteriorly. The presence of fourth
and/or fifth metacarpal dislocation in five of our six cases supports this
conclusion. The distal surface of the hamate, which is concave, articulates
with the convex base of the fourth and fifth metacarpals. With posterior
displacement, the metacarpal base strikes the dorsal lip of the distal
hamate and separates a coronal flake of bone, as shown below.
dorsal displacement of 4th and/or 5th metacarpal results in coronal
fracture
that separates fragment from dorsum of hamate
The radiographic appearance of the dorsal fracture of the hamate can
be confusing because the source of the bony fragment is not visible. However,
the presence of an oblong bony fragment projecting from the dorsal surface
of the carpus immediately proximal to the fourth and/or fifth metacarpal
bases should be specifically sought in patients with a posterior dislocation
of the fourth and/or fifth metacarpals. The differential diagnosis of a
bone fragment projecting from the dorsal aspect of the carpus should include
avulsion fracture of the triquetrum or other carpal bone and fracture of
the base of the fourth or fifth metacarpal.
Recognizing the dorsal hamate fracture is important clinically. Distal
carpal fractures associated with metacarpal dislocation are unstable injuries
and usually require internal fixation. Anatomic reduction of hamate-fourth/fifth
metacarpal joints is important as they are the most mobile of the carpal-metacarpal
joints.