Duck or wobbly gait is a common sign of congenital medullary dislocation. In unilateral dislocation, a limp appears, while in bilateral dislocation, the pelvis tilts forward when standing, the hips shrug backward, the waist bulges forward, and the abdomen bulges, so it is called duck or wobbly gait when walking from side to side, and when walking slightly fast, it is easy to fall. There are many theories on the etiology of congenital hip dislocation, such as mechanical factors, endocrine-induced joint laxity, primary acetabular dysplasia and genetic factors. There is mechanical stress from abnormal hip flexion during breech delivery, which can lead to posterior dislocation of the femoral head. Ligamentous laxity was once thought to be an important pathogenetic factor. Increased maternal estrogen secretion in late pregnancy causes pelvic laxity, which facilitates delivery and also produces corresponding laxity of the fetal ligaments in utero, making it easier for femoral head dislocation to occur in the neonatal period. However, it is difficult to explain the cause of the disease by a single factor, and it is generally believed that genetics and primary germ plasm defects may play an important role in the pathogenesis. The fetal hip begins as a cleft formed by interstitial cartilage, which is first deeply concave and round, then gradually becomes shallow and semicircular. At birth, the ilium, sit bones, and pubic bone are only partially fused, and the acetabular fossa is extremely shallow, so the fetal hip has a large range of motion during delivery in order to allow the fetus to pass easily through the birth canal. Therefore, the fetus is most prone to hip dislocation during the period before and after birth. If the lower limbs of the fetus are placed in the extended and internal position, the femoral head is not easily placed deep in the acetabulum, and it is very easy to dislocate.