A Bennett's fracture is:

B. Displaced by the pull of the abductor pollicis longus and adductor pollicis.

DISCUSSION: A Bennett's fracture is an intra-articular fracture of the proximal end (base) of the thumb metacarpal. The resulting bone fragment is held by the intermetacarpal ligament. The base of the metacarpal is displaced laterally by the pull of the abductor pollicis longus. The adductor pollicis pulls the proximal phalanx and distal metacarpal toward the palm and the proximal metacarpal away from its adjacent fracture fragment. These forces acting on the fracture tend to displace the metacarpal, usually making cast treatment alone ineffective. Treatment is by percutaneous pinning if closed reduction can be achieved, or by open reduction and internal fixation if significant displacement cannot be corrected by closed methods. A comminuted T-type fracture of the base of the thumb metacarpal was described by Rolando.