O-shaped leg can be determined by the following methods: First, the distance between the femoral condyles on both sides is increased, the patient is lying on his back, the knee joint is completely straight, the patella is facing straight up, the bilateral inner ankles or the medial edge of the feet are in contact with each other, and the two femoral condyles can not contact each other and keep a certain distance. Secondly, both lower legs are crossed, both femoral epicondyles are in contact with each other, if both inner thighs are able to contact each other, it means that the thighs are normal, and the inversion deformity is located under the knee joint. Third, bilateral deformity asymmetry, from the pubic symphysis to make a plumb line, so that the inner edge of the foot and the plumb line contact, respectively, can measure the distance between the femoral epicondyle and the line, can also confirm the O-shaped leg. Fourth, X-ray examination can show that the upper tibial epiphysis is tilted, the intersection angle between the longitudinal axis of the tibia and the axis of the femur is often angular on the lateral side, and the normal physiological valgus angle disappears.