Inversion of the knee, commonly known as O-leg or rotundity, and valgus of the knee, commonly known as X-leg, are relatively common lower extremity deformities. In normal people, the angle between the femur and tibia is mildly valgus, about 5-7 degrees outward, but valgus and valgus deformities occur when the angle deviates from normal due to congenital developmental deformity or arthritis. If the angle is less than this, the deformity becomes an inversion, and if the angle is greater than this, the deformity becomes an ectropion. There is a simple way to detect inversion or valgus, that is, when the knees are close together, the two feet cannot come together as valgus; the opposite situation when the feet are close together, the knees cannot come together as valgus. Ectropion or valgus deformity can be due to either internal or external bony deformities of the knee joint. The most common cause of inversion and valgus is wear and tear and joint degeneration due to imbalance in the weight-bearing surface of the knee, which can worsen the existing deformity and create a vicious cycle. There are different treatments for different causes and ages of valgus and valgus deformities. In the elderly, the most important treatment after joint destruction is knee replacement to correct the deformity.