Crutches are used by dwarves to move around when injuries have limited their mobility. However, dwarves who have lost the use of their legs due to spinal nerve injuries will not acquire and use crutches; only broken/amputated legs/feet will trigger hospital staff to assign crutches as part of treatment.
In adventure mode crutches can be used to walk when one or both legs are disabled. If an uninjured adventurer carries a crutch in their hand the movement penalty of using a crutch will be applied. Once a crutch has been equipped, it will continue to be used until it is dropped from one's hands - throwing the crutch will not properly clear the "crutch-walking" status, nor will placing the crutch into a container (or subsequently dropping or throwing the crutch from said container); in order to stop crutch-walking, the crutch must be re-equipped and then dropped.
Crutches are made out of one wood log at the carpenter's workshop or one metal bar at a forge. Crutches are stored in a Finished Goods stockpile, and will be placed in bins when there is space available.