Why is the femoral head prone to ischemic necrosis? This is mainly due to the special characteristics of the bone structure and blood supply system of the femoral head: 1. Most of the femoral head is covered with articular cartilage, and there is a layer of subchondral bone under the articular cartilage and the cortical bone of the femoral head neck, forming a fixed bony shell that surrounds the cancellous bone – microcirculatory system in the femoral head. This bony shell has no extension, and when pathological changes such as obstruction or extrusion of capillaries inside and outside the bony shell occur, it is impossible to expand outward and can only be squeezed inward, which can easily form intraosseous high pressure and further aggravate the destruction of blood supply to the femoral head, forming a vicious circle. 2, the blood transport of the femoral head mainly relies on the medial femoral artery supply, and there are also external femoral artery, head concave artery and proximal femoral trophoblastic branches. However, there are few mutual traffic branches with each other. The medial femoral artery supplies the femoral head from the femoral head-neck junction and mainly supplies the weight-bearing area of the femoral head. Because the femoral head is not as rich in collateral circulation as other bony tissues with soft tissue attachments, its microcirculation has few branches of communication with other blood supply systems, making it difficult to establish collateral circulation with other vessels when the blood supply to the femoral head is affected. These factors cause the blood supply to the femoral head is very fragile, once the femoral head main supply vessels are broken or blocked (traumatic), or because of some factors caused by the femoral head capillary occlusion and extravascular compression increase (alcoholic or hormonal) resulting in the femoral head within the blood flow is impaired, the femoral head is prone to osteonecrosis. 3. Osteonecrosis of the femoral head is mainly due to mechanical interruption of the supply vessels of this branch of the medial femoral artery and vein (traumatic), hormonal or alcoholic causing intra-capillary microcirculatory obstruction (intravascular coagulation or clotted fat emboli) and vascular compression occlusion (increased extravascular fat cells forming pressure on the capillaries), resulting in insufficient blood supply to the femoral head, followed by ischemic changes. At this time, the bone trabeculae supporting the femoral head disappear one by one due to ischemic necrosis, and the force supporting the femoral head is weakened until the femoral head is unable to withstand the body pressure, resulting in the collapse and deformation of the femoral head. The development to the late stage of ischemic necrosis of the femoral head. 4, foreign research shows that osteonecrosis is a multi-factor caused by the disease. In an anatomical study of a group of 99 hip femoral head necrosis with vascularized fibula grafts, 93 hips (94%) had abnormalities in the type of blood vessels. As a control, only 31% of the controls had vascular type abnormalities, with ascending vessel agenesis or dysplasia being the most common type of abnormality. These findings reveal that certain patients are at greater risk of developing ischemic necrosis of the femoral head because of abnormalities in the microvascular circulation of the femoral head.