If one arm has been crippled, the character is unable to use two-handed weapons like hammers, rifles and big guns. If both arms have been crippled, it is not possible to attack with weapons. This can be cured by visiting a doctor or using the Doctor skill.
Weapon accuracy is reduced in V.A.T.S. by a crippled arm, but still allow using weapons. In first person mode, the held weapon will sway, and while this may not seem to affect accuracy with regular non-V.A.T.S. shots, it does make the crosshairs sway significantly while using the scopes on weapons like a sniper rifle or scoped .44 Magnum, making it much harder to aim. A crippled arm can be healed by sleeping, visiting a doctor, using a doctor's bag, or applying a stimpak on the crippled arm.
For more information on crippled limbs, see Crippled Limbs.
Fallout 3 exploitEdit
Fallout 3 has a mechanism that gives any non-player character a certain amount of ammunition when they equip a weapon so that they can use it. Since this amount is usually much higher than the amount non-player characters usually carry, and since crippling an opponent's arms will make them drop their current weapon and try to pick it up again, this can be exploited. When encountering an enemy using a gun with desired ammunition, their arm can be crippled, then letting them pick up and re-equip the weapon (and get the bonus ammunition), then do the same thing again with their other arm so that they get the bonus ammunition again when they pick up the weapon the second time.
For example, an non-player character equipped with a minigun usually has around 50 5mm rounds on them, but crippling their arm once and allowing them to recover their weapon will increase the number to around 150 rounds; doing so again will further increase the number of 5mm rounds to about 250. Obviously, this can be used to get very large amounts of ammunition compared to what would normally be found. This technique is best utilized on opponents with Big Guns that have large magazines such as a minigun, Gatling laser, or possibly a flamer, but potentially any ranged weapon will do. Please note that super mutant overlords carrying a tri-beam laser rifle will not drop their weapon if their left arm is crippled. This can still be used in Fallout: New Vegas but the reduced number of enemies using weapons with large magazines will greatly reduce the utility of this exploit.