Osteonecrosis can occur in any part of the human body, and only for ischemic necrosis has been found more than 40, while the highest incidence of femoral head necrosis, which is mainly determined by biomechanical and anatomical characteristics. Because the femoral head is the terminal vessels are fan-shaped 20 – 25 branches, forming an arterial and venous ring at the cephalocervical junction, which originates from the internal and external spinous femoral artery. (1) Heavy load. The hip joint is the largest joint in the human body, supporting the weight of the entire trunk, the pressure between the head and the socket is bound to increase, maintaining this greater pressure for a long time, not only easy to cause structural damage, but also affect the local blood ring. (2) Shear force in. Hip joint is different from other weight-bearing joints as the two bone ends of the joint force line vertical, the femoral stem and the femoral head neck between the formation of 132 degrees of the angle, the gravity of the trunk is from the acetabulum through the femoral head, the neck migrated to the femoral stem, the force line is not vertical, it forms a shear force. Therefore, the physiological pressure on the head and neck is much greater than that on other joints. (3) Large range of motion. The range of motion of the hip joint is second only to the shoulder joint, extension, adduction, abduction, rotation, etc. It can accomplish all axial movements and has more chances of injury. (4) Less blood supply. The blood supply to the femoral head mainly relies on the lateral supporting band and the medial supporting band arteries emanating from the extracapsular arterial ring. The amount of anastomosing branches of the vessels is small and weak, and when one vessel is blocked and the other cannot compensate in time, it will cause the impaired blood supply to the femoral head.