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.
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.
Dwarves hold crutches like any other object and may use them in self-defense.
 Adventurer mode
In adventurer mode crutches can be used to walk when one or both legs are disabled. The associated skill is crutch-walking, and this can be trained to increase movement speed while using a crutch. It is possible to train crutch-walking without having an injury, however any adventurer carrying a crutch in their hand will have the movement penalty of using a crutch applied. It is possible to sneak while using a crutch. The crutch-walker status remains in effect while swimming. It is possible to aim attacks using crutches if you are holding one.
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. It may then be picked up and stored in a backpack with no status applied.
It is not currently possible to craft crutches in adventurer mode. Due to the current store-type imbalance in adventure mode they may be difficult to find for sale in shops. Crutches are most easily found during exploration of fortresses, camps or other places that have loot lying around.