There are several factors that can cause the leg to bend at the knee, one factor is developmental abnormal bending at the knee, and the other factor is degenerative abnormal bending at the knee. Developmental bending of the knee is more common in clinics, such as inversion of the knee, called O-shaped leg, and eversion of the knee, called X-shaped leg, which is most common in adolescents, mainly due to insufficient calcium supplementation in childhood or other causes of developmental abnormalities. After middle-aged and old age, there are degenerative knee abnormal bending, such as knee osteoarthritis for a long time, resulting in unequal width and height of the inner and outer knee joint gaps, thus causing the knee joint to turn inward or outward, which is also an important factor causing abnormal bending of the knee joint, and it is a common clinical deformity, which needs to be taken measures to treat.