Krackow classifies inversion of the knee into seven types and proposes solutions for each type. 1, Type I (simple bone loss type): usually due to bone wear on the lateral tibia, without medial soft tissue contracture or lateral soft tissue laxity. 2.Type II (lateral collateral ligament laxity type): the deformity of the coronal plane is more serious than type I. The deformity is usually still correctable during physical examination. 3.Type III (medial structure contracture type): the lateral structure is normal, and the deformity cannot or can only be partially corrected. 4.Type IV (diaphyseal deformity type): the deformed part of the bone is far from the joint, and the epiphysis is normal, often due to the deformed healing of tibial fracture. 5.Type V (medial contracture and lateral laxity): Although it has both the problems of type II, the treatment is the same as that of type III. 6, Type VI (epiphyseal and metaphyseal developmental abnormalities): In patients with internal derangement of the knee, the dysplasia is usually located on the tibial side, and the entire medial ligamentous joint capsule is often structurally shortened. The force line misalignment due to developmental abnormalities can be exacerbated by wear and tear of the osteoarthrosis and can also be complicated by Type II, III or IV conditions. Type VII (developmental stem curvature or acquired metaphyseal malformation type): the most common cause is overcorrection of the high tibial osteotomy in patients with knee valgus. When the osteotomy site is located at a ligamentous stop or a previous ligamentous stripping has been performed, then both skeletal and ligamentous abnormalities are present. Indications for internal derangement of the knee: severe internal derangement of the knee, two ankles touching each other, unilateral internal derangement of >5cm between the knees; bilateral derangement of >10cm or more, causing walking difficulties or knee pain should be performed orthopedic osteotomy. Preoperative preparation for internal derangement of the knee: 1. The main part of the deformity should be determined before surgery to determine whether the internal derangement of the knee is mainly caused by the deformity of the tibia or the femur. If the femur is the main deformity, femoral osteotomy should be performed; if the tibia is the main deformity, tibial osteotomy should be performed. In a few cases of severe deformity, both femur and tibia have obvious deformity, then both should be performed osteotomy successively with an interval of about 8 weeks. A simple and effective way to judge the deformity is to observe the whole lower limb under X-ray fluoroscopy to determine the main part of the deformity. 2.Measure the osteotomy site and osteotomy angle. If the bone deformity is the main part, take an X-ray film including the deformed bone and its upper and lower two joints, if the joint deformity is the main part, take an X-ray film including the joint and most of its upper and lower two bones to decide the osteotomy site. The angle between CD and EF is the angle that needs to be corrected, which is the top angle for wedge-shaped bone removal (or the top angle for wedge-shaped bone grafting in linear osteotomy). The osteotomy plane A’B’ (i.e. parallel to AB) should be chosen at the intersection of the CD and EF lines, which is ideal. The closer to the joint, the more accurate the correction, but there should be a certain distance from the epiphysis, and the site of plate fixation should be left to avoid injury to the epiphysis. Generally, the appropriate part of the epiphysis is chosen. Then make a vertical line GH of EF, intersecting with A’B’ in the lateral femoral cortex, and the wedge-shaped bone at the angle of the two lines is the bone to be removed. 3.The choice of wedge-shaped osteotomy or wedge-shaped bone graft. (1) wedge-shaped osteotomy, that is, according to the design of the removal of a wedge-shaped bone, after correction of deformity and restoration of normal force line, the two bone ends can be closely together; (2) wedge-shaped bone graft, that is, a linear-shaped osteotomy, according to the design of the correction of deformity, the formation of a wedge-shaped defect between the broken ends of the bone, another bone block graft filling. Both have their advantages and disadvantages: after wedge-shaped osteotomy, the limb is slightly shortened, but the chance of non-healing is very small; while after wedge-shaped bone grafting, the limb grows slightly, but the healing time is longer and there is a possibility of non-healing. Wedge resection is usually used clinically. Unless the trunk appears to be short compared with the lower limb, or is more shortened than the contralateral lower limb, and the limb deformity is not heavy, and the bone defect after osteotomy is not expected to be too large, wedge-shaped bone grafting can be used.