O-legs, i.e. inversion of the knee, can be caused by calcium deficiency, heredity or imbalanced causes such as poor sitting posture. Jumping rope does not help to improve O-legs, and different treatments should be adopted for different age groups. 1. Adolescents or infants: Adolescents or infants with immature bones can be corrected with straps or braces. 2. Adults: Adults with mature bones can correct the deformity slowly with osteotomies assisted by external fixation braces. 3. Elderly people: If the elderly people are accompanied by osteoarthritis and have severe joint pain, they can undergo knee replacement, which can relieve knee pain and correct the inversion of the knee joint at the same time. O-shaped legs should go to the hospital, under the guidance of the doctor for targeted treatment.