A bent inward knee is also called an external knee deformity. There are two common causes of knee valgus deformity: the first, congenital abnormalities of the tibia and femur; and the second, degenerative osteoarthritis in the elderly. Currently, there are two surgical methods to treat the deformity of knee valgus: the first is to correct the deformity of knee valgus by osteotomy, which can be done by osteotomy of the femur and tibia at both ends of the knee to correct the knee valgus, thus restoring the line of force to the lower extremity. The second type, if the patient is elderly and caused by degenerative osteoarthritis, often chooses a surface replacement of the knee joint, which can correct the deformity of knee valgus by effectively osteotomizing the surface of the knee joint. So the knee bends inward and can be corrected in two general ways: first, by osteotomy; and second, by surface replacement of the knee joint.