O-shaped legs mean that when the patient’s feet are together, the legs appear in the shape of an O. The main causes of O-shaped legs include vitamin deficiency, poor posture, and diseases. 1. Vitamin deficiency: The main reason for the formation of O-shaped legs is the lack of vitamin D during the growth and development of children, which can lead to abnormal bone development. 2. Incorrect posture: If children walk in an incorrect posture, stand with uneven weight on their legs, and often stilt their legs, etc., it will lead to the formation of O-shaped legs. 3. Diseases: O-shaped legs can also be formed if the child suffers from other diseases, such as osteoarthritis of the knee joint and rickets. It is suggested that if parents find that their children have a tendency to have O-shaped legs in infancy, they can follow the doctor’s advice to use a brace to correct it, and if it seriously affects their lives, they can have surgical treatment, such as joint replacement surgery.