The reasons for the formation of O-shaped (type) legs include excessive obesity and overweight, localized fibrocartilage dysplasia, rickets, post-traumatic deformity, post-infectious deformity, Brown’s disease, osteogenesis imperfecta, osteoarthritis of the knee joint, and so on. O-shaped leg refers to the legs together, bilateral ankle contact together, there is an inaccessible gap between the bilateral knee joints, the entire lower limb in the shape of the letter O, commonly known as O-shaped leg. O-shaped leg patients with the distal end of the knee joint to the inward curvature, so the scientific name is “knee inversion”. In children, physiologic knee valgus does not require treatment, while pathologic knee valgus can be treated with braces or surgery depending on the extent of the disease. In adults, mild asymptomatic varus knees usually do not require treatment, while severe varus knees need to be treated as soon as possible. If the presence of O-shaped leg is suspected, it is recommended to seek timely medical treatment under the guidance of a doctor to avoid delaying the condition.