Are there any hand, wrist or arm fractures that cannot possibily be caused by a fall on an outstretched hand? I'm a mystery writer and need an injury that could be due to someone deflecting the arm of a gun-wielding perp.

Your . Your best bet is probably what is called the "nightstick" fracture. If you need some technical help, i could help with the ways to distinguish a "direct mechanism" fracture from an "indirect" one. While an ulnar shaft fracture can be caused by a fall, the pattern would be slightly different from a true "nightstick.".
Agree . Agree with night stick traditionally a midshaft ulna fracture from direct blow an arm injury is often a midshaft humerus fracture, also a direct blow but of significantly greater force. A boxers fracture, a fracture of the fifth metacarpal neck from a blow to a wall or a face.Sometimes called a fighters fracture because a true "boxer would punch with the middle knuckle. While the fighter would throw a punch incorrectly. A leash or rope injury with torque or rotatory force on a finger will cause a spiral fracture of a metacarpal. A fracture of a phalanx a crush injury can occur of the distal phalanx with a comminuted or fragmented fracture a door injury is common for a proximal phalanx fracture especially in a child of the proximal phalanx neck. There are many more depending upon your dramatic scenario if you want more i also will be happy to speak with you more about this.