CDH (congenital dislocation of hip joint), also known as developmental hip dislocation or developmental dysplasia of the hip (DDH) and hip dysplasia, is a common congenital malformation in which the femoral head loses its normal relationship with the acetabulum in the joint capsule, so that it cannot develop normally before and after birth. Clinical manifestations: 1, neonatal and infantile manifestations (1) joint movement disorders affected limb is often flexed, poorer than the healthy side, pedaling power is located on the other side. The hip joint abduction is limited. (2) Shortening of the affected limb The affected femoral head is dislocated posteriorly and superiorly, and the corresponding shortening of the lower limb is common. (3) Changes in skin wrinkles and perineum The skin folds on the buttocks and inner thighs are asymmetrical, and the skin wrinkles on the affected side are deeper and more numerous than those on the healthy side. In female infants, the labia majora are asymmetrical and the perineum is widened. 2, early childhood manifestations (1) lameness gait lameness is often the only complaint of parents when the pediatrician visits the clinic. In the case of bilateral dislocation, the child has a “duck gait”, a pronounced posterior protrusion of the buttocks and an increased lumbar foreshortening. (2) In addition to the shortening of the affected limb, there is also inversion deformity. (1) According to the relationship between the femoral head and the acetabulum, it can be generally classified into the following three types. ① congenital dysplasia femoral head only slightly shifted outward, the Shenton line is basically normal, but the CE angle can be reduced and the acetabulum becomes shallow, Dunn called this congenital hip dislocation grade I. ②The congenital subluxation femoral head is displaced outward and upward, but still forms an articulation with the lateral part of the acetabulum, the Shenton line is discontinuous, the CE angle is less than 20°, and the acetabulum becomes shallow, which belongs to Dunn’s classification grade II. (3) Congenital complete dislocation of the femoral head is completely outside the true acetabulum, forming an articulation with the lateral part of the ilium and gradually forming a false acetabulum, while the original joint capsule is embedded between the femoral head and the ilium, which belongs to Dunn classification grade III. (2) According to the degree of dislocation, there are 4 degrees of dislocation as follows: ① Ⅰ degree dislocation of the epiphyseal nucleus of the femoral head is located below the Y line and outside the vertical line of the external upper edge of the acetabulum. ② Ⅱ degree dislocation of the femoral head epiphyseal nucleus is located between the Y line and the parallel line of the upper edge of the socket of the Y line. ③ Ⅲ degree dislocated femoral head epiphyseal nucleus is located at the height of the parallel line of the upper edge of the socket. ④ Ⅳ degree dislocated femoral head epiphyseal nucleus is located above the parallel line of the superior margin of the socket, and there is pseudosocket formation.