A sprain involves the wrenching or twisting of a joint, with partial rupture of the joint ligaments. There may also be damage to nearby blood vessels, muscles, tendons, and nerves. A sprain is more serious than a strain which is the overstretching of a muscle, without swelling. Severe sprains are so painful that the joint cannot be used. Swelling which can be considerable is often accompanied by redddish or blue discoloured tissue because of bleeding from ruptured blood vessels.