I. What is Developmental Dysplasia of the Hip? Developmental Dysplasia of the Hip (DDH), formerly known as Congenital Dislocation of the Hip (CDH), is a general term for a group of pathologies characterized by spatial and temporal instability of the hip joint during development, including hip dislocation, subluxation and acetabular dysplasia. DDH can cause abnormal gait, abnormal development of adjacent joints, and secondary spinal deformities in children, leading to lower back pain and pain caused by degenerative hip joint degeneration in adulthood. The goal of DDH treatment is to achieve a stable concentric reposition and avoid ischemic necrosis (AVN) of the femoral head. Early diagnosis and treatment is the key to improve the outcome. Second, how to diagnose? Early diagnosis mainly relies on ultrasound screening and physical examination. The earlier the diagnosis is made, the better the treatment effect. For infants and children, the diagnosis is clearer, and for the morphological changes of soft tissues in the hip joint cavity, the diagnosis can be made by arthrography. Differential diagnosis: 1, septic hip osteoarthritis in infants and young children: the index of the acetabulum is normal on x-ray, and there is a history of infection such as fever and local soft tissue swelling in the past history of the child. 2, congenital hip entropion: the onset of the disease is older, usually obvious only after the age of 3 to 4 years, negative overlap test, x-ray stem neck angle is often between 80 to l00 °. Fourth, how to treat? (1) Birth to 6 months: This stage is the prime time for DDH treatment, with simple and easy methods, good compliance, reliable efficacy and few complications. (2)7 months～18 months：With the increase of age, weight and activity increase, the compliance and efficacy of using sling decreases. Treatment: Prefer closed repositioning under anesthesia and plaster tube type fixation in human position. (3) Treatment from 18 months to 8 years (walking age): closed reduction is still possible on a trial basis up to 2 years of age, but most children require incisional reduction and osteotomy. Osteotomy of the pelvis and proximal femur not only corrects the deformity of the acetabulum and proximal femur itself, but also provides stability after resetting. Currently, there is a common international phase I surgical treatment; incisional repositioning, pelvic osteotomy, and proximal femoral osteotomy. Preoperative traction is not required. (4) Over 8 years old (older DDH):Indications are less clear, surgical operation is difficult, surgical complications are numerous, and the efficacy is uncertain, so it should be used with caution and with the participation of an experienced and dedicated surgeon.