@EdRick - You're right, nursemaid's elbow is a soft tissue injury. The connection to this topic is that it probably involves the styloid process of the radius. It's basically a dislocated elbow and the head of the radius gets pushed out of place.
You don't say how close you are to this friend, but I hope she has found out exactly how her son got this injury. The difference between this and a chauffeur's fracture is that while the chauffeur would be the victim of the fracture, the nursemaid would be the one causing nursemaid's elbow.
It can be caused either by roughhousing (i.e., swinging the kid by his arms) or by abuse; either way, you need to know who did that to your kid so you can make sure it never happens again. My niece had this injury, apparently when a poorly trained day care worker yanked on her arm to try to make her go outside. The day care people had some other story about the monkey bars, but my sister found her a better place.