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 deformities of the spine in children, leading to lower back pain and degenerative hip joint degeneration in adulthood. Pain caused by DDH. Because the disease is closely related to the developmental process of the hip joint, the presentation and corresponding treatment varies among age groups. The goal of DDH treatment is to obtain a stable concentric reposition and avoid ischemic necrosis (AVN) of the femoral head. Early diagnosis and treatment are the keys to improve the outcome. (a) 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. 1. Clinical manifestations and signs: asymmetry of thigh skin pattern and hip pattern, joint popping and unequal length of lower limbs. Positive hip abduction test on the dislocated side. Ortolani/Balow sign is positive. Inequality of limbs, positive Allis (Galleazzi) sign, etc. 2. Imaging: Ultrasound examination of the hip joint is preferred for children ≤4 months old, Graf method; X-ray double hip orthopantomographs can be taken for children >4 months old, commonly used indicators are Perkin’s square, acetabular index (AL), central marginal angle (CEA), Shenton’s line, tear drop (Teradrop) sign. 3, Treatment: Pavlik sling is preferred to maintain hip flexion at 100°~110° and abduction at 20°~50°. 24 hours maintenance. Prohibit dislocation movements (including examination and changing clothes). Regular ultrasound examinations, 1 time/1 to 2 weeks. If the ultrasound indicates concentric repositioning after 3 weeks, continue to maintain for 2 to 4 months. An abduction brace was then used until the acetabular index (AL) was <25° and the central marginal angle (CEA) was >20°. If ultrasound and clinical examination after 3 weeks suggest that no repositioning has been achieved, the Pavik sling is discontinued and other treatment is used instead. Otherwise, persistent compression of the acetabular wall by the posteriorly dislocated femoral head can lead to sling disease (dysplasia of the posterior acetabular wall). Other treatment methods include bracing (fixation position is the same as the sling) or direct closed cast fixation. Non-anesthesia repositioning and wearing extreme (frog) abduction brace are contraindicated to avoid damage to the femoral head cartilage and AVN. (2) 7 months～18 months The compliance and efficacy of using the sling decreases with the increase of age and weight and activity. 1. Clinical manifestations and signs: In addition to the above-mentioned manifestations, physical examination shows asymmetric appearance of both hips, wide perineum, high position of the greater trochanter, positive telescope sign (telescope sign) and Allis sign. 2. Treatment: Closed repositioning under anesthesia and plaster tube fixation in human position are preferred. Before closed repositioning, the internal longus muscle should be cut or cut percutaneously, and if necessary, the iliopsoas tendon should be cut at the same time, and repositioned by gentle Ortolani technique. The observation index is a safety zone >20°. Arthrography with Onyepek is recommended. If the angiogram shows a gap of >4 mm between the cartilage margin of the femoral head and the inner wall of the acetabulum, it suggests soft tissue impaction between the head and socket, which prevents repositioning. Abandon closed repositioning and use transmedial approach or anterolateral approach to perform incisional repositioning instead. Preoperative skin traction is feasible for 1-2 weeks, or for several weeks to achieve repositioning. After repositioning, the hip was fixed in a human plaster cast for 100° of flexion, 40-50° of abduction, and neutral rotation for 3 months, and then the cast was replaced and continued to be fixed in a plaster cast or brace for 3-6 months. At the end of the above treatment, the child has the following conditions: ① concentric cephalo-acetabular repositioning, observation; films are taken every 6 months; ② cephalo-acetabular repositioning, but residual acetabular dysplasia, manifested by steep and straight acetabulum, AI>24°, but continuous Shenton line, wearing an abduction brace, especially at night; films are taken every 4 months to observe the improvement of acetabular inclusion (AI, CEA) or whether there is semi (3) Residual subluxation, as evidenced by discontinuity of the Shenton’s line, usually associated with acetabular dysplasia. An abduction brace may be worn and the patient should be reviewed every 3 months for a total of 6 to 12 months. If the radiographs show persistent subluxation (Shenton’s line discontinuity), surgical correction should be performed; if it continues to improve, the treatment should be the same as ②; ④ For residual AVN, the affected femoral head should be placed under the inclusion of the acetabulum to allow for repair and shaping. The specific treatment is the same as ② and ③.