As many people already know, osteoarthritis of the hip joint, rheumatoid arthritis and aseptic necrosis of the femoral head can cause serious destruction of the joint function. The 10-year survival rate for artificial joint prostheses is usually above 95%, and the 15-20 year survival rate is also generally above 80% or even 85%. Total hip arthroplasty has been one of the most successful surgeries in the field of orthopedics. However, for young patients, total hip arthroplasty is a big problem, because the total amount and intensity of activity of young patients is much greater than that of elderly patients due to the need to live and work, and even with the same amount of activity, the stress load on the prosthesis brought by their strong surrounding muscles is very different from that of elderly patients. In addition, the younger the patient, the shorter the life span of the prosthesis, and the patient has to face the painful fate of multiple revision surgeries during his lifetime. Therefore, for young patients, traditional total hip arthroplasty is obviously not a good choice, but only a last resort, so many doctors often ask patients to “endure a few more years” and wait until they are older before having total hip surgery. However, the consequence of “pain tolerance” is a huge sacrifice in quality of life. Hip surface replacement is a very good alternative to this dilemma. Unlike total hip replacement, surface hip replacement does not completely remove the bone of the proximal femur, but merely shapes the diseased femoral head and places a layer of hemispherical artificial metal articular surface to replace the original femoral head articular surface, the thickness of this layer of metal is usually about 3 mm, in other words, this surgery only replaces the articular surface of the femoral head, hence the name surface replacement In other words, this procedure replaces only the surface of the femoral head, hence the name surface replacement. For the acetabular side, the long-term survival rate of non-cemented acetabulars in younger patients is satisfactory, so acetabular replacement is usually performed as well. However, unlike conventional total hip arthroplasty, in order to preserve as much of the acetabulum’s own bone mass as possible while accommodating the same size of the femoral head, it is necessary to make the artificial cup very thin, about 3-5 mm thick, also replacing only the “surface”. Moreover, in order to have good frictional properties with the femoral head, the inner wall of the surface replacement cup must be smooth and continuous, and no holes can be made in it, so that such a cup cannot be fixed to the pelvis from the inside with screws, which is another difference from total hip replacement. In very young patients, if the acetabulum itself is of very good quality, it is possible to perform a hemi-acetabular surface replacement instead of an acetabular replacement. These concepts of hip surface replacement were developed over many years and the current hip prosthesis is actually a third generation prosthesis. Because of these characteristics, the operation of hip surface replacement surgery is technically difficult and demanding, in two ways. On the one hand, the neck of the femoral head is not removed as in the case of total hip replacement, so the space is cramped during the surgery, the surgical exposure is demanding, and there is little room for operation; on the other hand, the area where the femoral head and acetabulum are removed and replaced is very small, so the artificial head and cup can only be 3-5 mm thick, and there is little room for adjustment, and the head and cup of the prosthesis can only be matched one-to-one in size. For example, if the original measurement of the femoral head is 40mm OD, then the femoral head can only be shaped to 34mm, so that 3mm is added on each side, which is exactly the thickness of the femoral head prosthesis, while the acetabulum can only be ground to a maximum of 45mm ID, and then a prosthetic socket cup with an OD of 46mm and an ID of 40mm and a wall thickness of 3mm is installed. This shows that hip surface replacement, like other arthroplasties, operates on a millimeter scale, but requires far more precise control than conventional arthroplasty. The 1 mm gap between the outer diameter of the prosthesis and the internal diameter of the bony acetabulum is obtained by the metal squeezing the bone when the prosthesis is driven in, called press fit, which allows for better initial stability of the prosthesis. But extrusion can cause metal deformation, so that the spherical surface does not match; furthermore, the forging, high temperature, annealing and other processes during processing may cause deformation, so that the spherical surface is not whole, the process of prosthesis production and processing must take these factors into account. In addition, the outside diameter of the femoral head prosthesis is actually slightly smaller than the internal diameter of the socket cup prosthesis, about a few dozen microns, called the tolerance zone. The tolerance zone gap will be filled by the joint fluid, a thin and thin layer of liquid like a membrane to separate the two sides of the metal, not only to shorten the wear period, but also greatly improve the friction performance, almost close to zero friction, this state of friction is called “liquid film friction”. Thus, the production of surface hip prostheses is very demanding, and their frictional properties are close to ideal. The gold-on-gold surface hip arthroplasty preserves the proximal femur bone to the maximum extent and reconstructs the local mechanical environment close to the “natural” one, thus providing excellent intrinsic joint stability and a near physiological range of motion, with less postoperative limb inequality, deep squatting, and very little dislocation. The functional recovery of the hip is significantly better than that of conventional total hip replacement, and most importantly, the difficulty of revision surgery after long-term failure of an epiphyseal hip replacement is very low, equivalent to that of an initial total hip replacement, which allows young patients to live an active life for a considerable period of time. This procedure can spare young patients from unnecessary painful waiting and restore their proper vitality in the golden age of life, while preserving the opportunity for future total hip replacements, which buys the patient a high-quality young adult period of 15-20 years or even longer Combined with the above characteristics, epiphyseal hip surgery is particularly suitable for young, active patients with high postoperative motor function requirements, and, at present, because life expectancy is getting longer, there is a tendency to use epicondylar hip surgery in patients under 60 to 65 years of age to reduce the complexity and high cost of subsequent revision surgery. Epiphyseal hip surgery is not suitable for elderly patients over 60 to 65 years of age, who often have a degree of osteoporosis that can affect the fixation of the femoral head prosthesis and are more prone to intraoperative and postoperative femoral neck fractures. In terms of specific diseases, hip surface replacement can be suitable for osteoarthritis, femoral head necrosis, developmental hip dysplasia, rheumatoid arthritis, ankylosing spondylitis involving the hip joint, traumatic arthritis, etc., provided that the local anatomical structure is not too abnormal. The development of modern joint replacement technology also provides some other solutions for patients who cannot undergo hip surface replacement due to anatomical abnormalities, which we will have the opportunity to discuss with you later.