My friend's 2 year old was playing on some slippery surface (a "sprinkler park"), and fell. She was not concerned (2 year olds fall all the time, and he had no visible scratches) at first, but when he would try to walk, his knee (or hip or ankle?) would kind of "buckle" underneath him. He is not in any pain; no reddness or swelling either. He is jumping and squatting, but walking strangely. The most noticeable was an hour later: he went to kick a ball with his right leg, while standing on his left leg...and his left leg just "gave out". We can't notice any deformities or anything.
We called the nurse-on-call after-hours (it's a Sunday), and were told to do the "wait and see". Give him ibuprofen if it swells. He is eating and sleeping fine. If he still has trouble tomorrow morning, my friend will take him to the doctor.
Just wondering if this has happened to anyone else? Nurse said if strain, sprain or dislocation, there would be pain and he would not voluntarily move the injured leg. He is not doing this for attention, so can rule that out, too. What injury could this be, without pain?