“……if this anteversion is more than about 30 degrees, she will probably demonstrate a lack of external rotation.
The opposite of anteversion is femoral retroversion. This occurs when the angle of the femoral neck and head as it enters the acetabulum is less than 10 degrees. In this case, the student will demonstrate an extreme limitation of internal rotation.
The position of most stability in the hip joint is not this neutral or Tadasana position. Instead, the position of most stability for the hip joint is when the femur is in slight abduction, flexion, and external rotation. You can experience this position for yourself. Stand up and imagine that you are going to pick up a heavy load. As you imagine yourself doing this, you will no doubt separate your feet, turn your feet slightly out, and bend your knees and flex your hips.……
……In fact, after total hip replacement surgery, the doctor recommends that the patient not ever cross her legs with the involved leg on top. If she does so, sitting in flexion, adduction, and internal rotation with the involved leg, she will be moving the head of the femur out of the socket and into the position of dislocation. Remember that the angle the neck of the femur has in neutral is a slightly forward position, so it is easier than you might think to move the head of the femur away from the acetabulum.”引自 第八章 盆骨、髋关节和股骨 - 关节