Overview of DDH: Developmental dislocation of the hip (DDH) is one of the most common and complex disorders in orthopaedic surgery. Its pathological anatomy is very complex, mainly manifesting in cephalic socket dysplasia and abnormal alignment, and the resulting stress changes in the corresponding area, leading to necrosis of the femoral head and hip joint hypofunction, further osteoarthritis, and premature replacement of the femoral head.DDH is a common limb deformity in childhood, and most children are found only after walking due to limping, with high complications such as joint mobility disorders and femoral head necrosis. It brings a great burden to the family and society; in the spectrum of diseases in domestic pediatric orthopedic units, DDH, however, always occupies the first place in limb deformity diseases, and a large number of DDH found at a late stage not only brings all kinds of difficulties to the treatment, but also causes great obstacles to the preservation of hip function after treatment; delayed diagnosis and treatment of DDH may lead to claudication and pain, and is one of the main causes of degenerative osteoarthritis in adults and acceptance of joint One of the main causes of degenerative osteoarthritis in adults and the acceptance of arthroplasty. Therefore, early diagnosis and timely treatment are of great importance. The development process of early screening for DDH Internationally, the early diagnosis of DDH has undergone a development process from the initial clinical maneuvering examination, later x-ray diagnosis, to the current extensive screening with ultrasound in the neonatal period. Since the early 1980s, when the Austrian scholar Graf founded the ultrasound hip examination technique, this technique has been widely promoted and popularized, and the early diagnosis of DDH by ultrasound has become an integral part of the newborn screening policy in many countries and regions, and through early ultrasound screening of the hip joints of newborns and small infants, a large number of children with DDH have received early diagnosis and early treatment. This has greatly reduced the local incidence of initial diagnosis of late DDH, not only improving the outcome of DDH treatment, but also reducing the difficulty and high cost of treating late DDH cases. Methods of hip examination Ultrasound assessment Graf method: Static assessment of morphology and structure of acetabular bone and cartilage, which allows quantitative typing and also pressure assessment of stability. Harcke method: dynamic assessment of morphology and stability. Mainly used in neonates. The disadvantage is that it cannot be quantified. X-ray: does not clearly show cartilaginous structures and early ossification and is indicated for infants over 5 months of age.