One-week-old baby O-shaped legs (also known as knee inversion) can be divided into physiological and pathological conditions, the former is a stage of growth and development, the latter is caused by rickets, poliomyelitis and other diseases. 1. Physiological inversion of the knee: it is a stage process of immature musculoskeletal development, which is a normal physiological manifestation. This kind of condition will be corrected by itself with the development of young children’s standing and movement, and generally do not need special treatment. 2. Pathological inversion of the knee: caused by rickets, bone fracture, poliomyelitis and other diseases, especially rickets is the most common, and this kind of situation can not be cured. To sum up, when the one-week-old baby O-shaped legs manifestation, we must promptly consult a doctor to find out the cause, do not blindly judge, dispose of their own, so as not to miss the treatment of certain diseases, resulting in adverse consequences.