O-legs in medicine is called knee inversion, one and a half year old baby knee inversion can be divided into physiological and pathological conditions, most of the former can be self-healing, the latter can not be generally self-healing. 1. Physiological inversion of the knee: is a stage in the development process of the body of the external manifestations of the process, there is no pathological abnormalities, inversion of the knee will be with the maturity of the development of the body to recover, corrected, generally do not need to carry out special treatment. 2. Pathological knee inversion: is due to rickets, bone fracture, poliomyelitis and other diseases caused by pathological changes in the knee joints, such cases generally can not be self-healing, the need for timely treatment of the original disease and lower limb deformity correction (including non-surgical and surgical methods), according to the cause of the targeted treatment. In summary, one and a half year old babies appear O-shaped leg performance, must seek medical treatment to identify the cause, do not judge on their own, blindly waiting for the condition to heal itself, in order to avoid delaying the treatment of the disease, resulting in adverse consequences.