O-leg and X-leg are common lower limb deformities in children and are one of the most worrying problems for parents of children with O-leg, also known as knee entropion, which mainly manifests itself by bending the lower limbs outward, widening the distance between the knees, and swaying when walking; when lying down, the lower limbs are straight, the patella is directly above, and when the inner ankles are together, the distance between the knees exists, and the greater the distance, the heavier the entropion. The main manifestations of “X” shaped leg, also known as knee valgus, are that both knees collide with each other when walking, easy to fall, and the toes are deviated inward; in the horizontal position, the lower limbs are straight, the patella is directly above, and when the knees are together, the distance between the bilateral inner ankles exists, and the greater the distance, the heavier the valgus. What are the causes of internal and external knee valgus? The causes of internal and external knee valgus are divided into two categories: physiological and pathological. Fortunately, the majority of knee valgus in childhood is physiological. There is a process of physiological changes in the development of the lower extremities from the newborn to the child, and mild or moderate inward bending of the lower extremities, including the tibia and femur, is normal in newborns and infants. This may be a continuation of the lower extremities in the mother’s body position. Inward curvature of the lower extremities can be corrected automatically with the development of standing and movement without any disturbing factors during the normal development of the child. Generally speaking, newborns and infants within 1 year of age have significant knee inversion; at 1-2 years of age, the lower extremities gradually become straighter; at 2-3 years of age, knee valgus occurs, and is most pronounced around 4 years of age, after which it is gradually corrected and approaches adult level by 7 years of age. Physiological knee valgus generally does not require special treatment and will correct itself with weight bearing and bone development. Some parents are afraid that their children’s legs will not be straight, so it is not right to bind the child’s legs after birth, which will affect the development of the child’s lower limbs or hip joint. There is also a pathological knee inversion, the main cause of rickets, trauma, inflammation, cerebral palsy, etc., can cause knee inversion and valgus deformity. These deformities are often serious and cannot be corrected on their own as the child grows and develops. What are the risks of internal and external knee valgus? If not corrected in a timely manner, severe internal and external knee valgus will affect the appearance of both lower limbs, walking gait, and affect the lower limb force line abnormalities, early onset of osteoarthritis, resulting in long-term joint pain and movement disorders. Which knee inversions need treatment? Pathological internal and external knee rolls usually cannot be corrected by themselves and are more serious, so surgical intervention is usually performed on the basis of treatment of the original disease. If the knee pitch or ankle spacing is still greater than 5 cm after the physiological correction period, usually at the age of 7 years, treatment is also required for knee inversions of unknown etiology. What are the current treatments for internal and external knee valgus? Conservative treatments such as massage and bracing have been proven to be ineffective and usually require surgical intervention. In the past, orthopedic osteotomy was the most common treatment. Although this treatment method is technically mature and has satisfactory results, it is very traumatic, bleeding and takes a long time for the fracture to heal, and the child has to experience long-term pain. This method is called 8-plate unilateral epiphyseal plate blocking, which gradually corrects the deformity by blocking the growth of one side of the epiphyseal plate and gradually correcting the deformity through the natural growth of the other side of the epiphyseal plate, which overcomes the shortcomings of osteotomy and orthopedics. The angle of correction can be controlled during dynamic observation, and it is suitable for almost all growing children. However, if the child has passed puberty, for example, if the boy has ejaculation and the girl has menstruation, then the best time for treatment is missed and osteotomy may be required to achieve the treatment goal. Therefore, parents should pay attention to their children’s growth and development, and if they find that their limbs are developing differently from other children of the same age, they should come to the pediatric orthopedics department in time to avoid delaying the best treatment.