With the gradual popularization of early screening for DDH in China, more and more children are detected within 3 months after birth and receive timely treatment. The term “DDH” is no longer unfamiliar to many parents, but they are full of doubts and concerns about it. The Department of Pediatric Orthopedics of Tianjin Hospital took the lead in carrying out city-wide DDH screening in 2009, and here we popularize the necessary knowledge in the early treatment of DDH for many parents. What is DDH? “DDH” is the abbreviation of developmental dysplasia of the hips, which is one of the most common birth defects of the bone and joint system in children. It is one of the common birth defects of the bone and joint system in children, and also the most common pediatric hip disorder, which means that the head of the femur is completely or partially dislocated from the acetabulum at birth or during later growth and development due to certain factors. It includes acetabular deformity, proximal femoral deformity, or both, and is divided into three types: (1) complete dislocation, in which the head of the femur is located entirely outside the acetabulum; (2) subluxation, in which the head of the femur is partially located outside the acetabulum, with the head and socket still in contact with each other; (3) dysplasia of the acetabulum, in which the acetabulum is steep and straight, and the acetabulum covers the femoral head poorly but the head of the femur is still located in the acetabulum (Figure 1). Figure 1. Radiographic presentation of DDH (yellow line is the acetabular contour, black circle is the femoral head) DDH is a dynamic disorder Previously, DDH has been referred to as congenital hip dislocation, meaning that the dislocation of the femoral head existed before the birth of the patient. In the last two decades, specialists have noted that some children are born with an unstable hip (subluxation or subluxation), but can gradually become a normal, stable hip as they grow and develop. Some children are born normal but develop acetabular dysplasia or acetabular dysplasia with femoral head subluxation, suggesting that hip dislocation is not entirely congenital. DDH encompasses acetabular dysplasia or dislocation that is present at birth, as well as acetabular dysplasia, subluxation or even total dislocation of the hip that occurs later in life as the child grows.DDH is a dynamic condition that may get better or worse as the infant grows. The exact cause of DDH is not fully understood. It may be related to factors such as race, geography, lifestyle, gender, position of the fetus in the uterus, and genetic mutations. Newborns born with any of the following factors: girls in breech position for the first time, family history of the disease, forefoot inward (metatarsophalangeal inversion), congenital clubfoot, strabismus, or a combination of lower limb deformities are all at high risk for DDH, and should be examined by a specialist for hip joints, except for hip joints with or without abnormalities, so as to avoid delay in treatment.