The informant first heard this saying from her mother in Washington, USA where the informant is from. This is an American saying that is used in a conversational setting. The informant states that this saying is used when somebody is trying to say that a situation is not serious at all and is silly. This is because, as she says, a rubber crutch is not very useful in any orthopedic ward, so this phrase is used to convey that. This is a folk metaphor and makes use of a silly concept to describe a situation as accurately as possible. The use of which the informant describes the saying  as makes sense. The phrase itself and the way its told has a humorous and silly tone to it, indicating that this is a piece of folklore that would not be performed in the professional setting, but rather, used in a casual conversation.