First, welcome to the forum silverdreamer. The answer to your question would be determined by the relationship between yourself and your injured person. In general if a person has a good sense of humor, a light greeting with a humorous phrase or joke would lighten the gravity of their injuries. Something like, "I just talked to the nurse and they operated on the wrong leg." If you don't have the green light for something humorous play it safe and let the person do the talking. Use a question greeting; eg., "Tell me all about it." You will probably get a full description of the accident, the trip to the hospital and all the details. Be prepared and the best greeting then is not to interrupt.