The pelvis refers to the pelvic skeleton connecting the spine and the lower limbs. The pelvis is a complete bone ring connected by the rear sacrum, the coccyx (the lowest two bones of the spine) and the left and right hip bones. The pelvis not only transmits the body weight to the two lower limbs , and as the basis for the activities of free lower limbs, but also support the protection of abdominal and pelvic organs.