your ER doc friend was probably referring to the femoral neck, the part of the femur that often breaks in little old ladies. It is the angled portion of the femur before it connects to the acetabulum, is the size described, and is a load bearing part of the "hip" joint. Take out the femoral neck and the person cannot stand. This is why little old ladies fall after their brittle bone fractures at this point.
Also, if you take out the "hip joint" itself, composed of the acetabulum (or "socket"), and femoral head (or "ball") of the ball and socket that comprose the hip, and that person cannot stand either.
Hit the femoral artery, and rapid exsanguination leads to unconsciousness (bleed out = pass out). Hows that for medical lingo?
I think that the point contended is whether or not a pelvic hit is a good stopper. The point is, it can be. But you gotta hit the right areas of the pelvis. Hit the load bearing areas, or plumbing and a pelvic hit can be effective. As effective as head, heart or spine? Probably not. Miss the "vitals" of the pelvis and it's much like a gut shot.
Just my 2 cents.