Final answer:
A splint should be applied in emergency care of extremity injuries to immobilize the affected area, reduce pain, prevent further damage to tissues, prevent misalignment of bone ends, and promote healing.
Step-by-step explanation:
In the emergency care of extremity injuries, a splint should be applied because it helps immobilize the affected area, reducing pain and preventing further damage to tissues. By stabilizing the bone ends, a splint can also prevent the bones from growing together in misalignment. Additionally, splinting allows for limited use of the broken limb while still promoting healing.