O-leg and X-leg are the common names for knee inversion and knee valgus. O-leg is also known as knee inversion, which means that when the human body stands with the feet together, the distance between the legs from the ankle up to the knee joint is getting wider and wider, and the distance between the legs from the knee joint up to the root of the thigh is getting narrower and narrower, so that the whole lower limbs of the bilateral lower limbs are formed in a shape similar to the letter O. X-leg is also known as knee valgus, which means that when the human body stands with the feet together as much as possible, however, the bilateral knees touch first, and both sides can not touch one another, resulting in the formation of a similar letter X shape of the lower limbs. Knee valgus refers to a condition in which the human body tries to keep the feet together when standing, but the bilateral knee joints are in contact first and the bilateral ankles cannot be brought together, resulting in the formation of a shape similar to the letter X on the bilateral lower limbs, which is why it is called X-shaped leg. The internal and external knee joints are mostly caused by genetic factors or acquired factors, such as walking posture, resting posture, practicing kung fu, training and other reasons, which lead to the laxity of the medial and lateral collateral ligaments, and the fixation strength of the lateral side of the knee joint is weakened and the internal and external knee joints are turned out. Long-term internal and external knee joints will lead to serious meniscus and ligament injuries, and they should be corrected and treated as soon as possible.