I've been working on anatomy, and today i was studying the human skeleton around the hip bone area and was just wondering what exactly happens to the hip joint and femur bone when someone does the splits?(sideways) does the bone go out of it's socket? or, something else?
Done right, then the ball joint stays in the same place it ever was, just pointing out to the side. Note how her legs are facing upwards; this should help you figure out how the upper thigh is oriented. If you look at this hip in a forward standing position [link] you will be able to see that when the leg is oriented to match the photo the "knob" on the outside of the femur will go behind her. Thus, it does not obstruct the movement.
Done wrong, you can dislocate your hip.
I really wish I had a posable human skeleton for these moments!
Kafine has it right, it essentialy just pivots in its socket. It can rotate anywhere around an axis as long as it is not obstructed by the pelvis or restrained by tendons.