Developmental hip dislocation is a relatively common deformity that used to be called congenital hip dislocation, but was renamed developmental hip dislocation or developmental hip dysplasia by the North American Society for Pediatric Orthopaedic Surgery in 1992. The incidence is 1 to 3.9 per 1,000. There are more females than males, about 6:1, more unilateral, more left-sided than right-sided, and less bilateral. The etiology and pathology of the disease is unknown, but it is related to genetic factors, and there is often a family history of the disease, and sisters or brothers may suffer from the same disease. Primary acetabular and femoral head dysplasia and laxity of the joint capsule and ligaments are the main causes. Fetal malposition in the uterus and hyperflexion of the hip joint is also a cause of dislocation formation. The pathological changes include both skeletal and soft tissue changes, and the changes become increasingly aggravated with age 1. skeletal changes 2. soft tissue changes 2. clinical manifestations and diagnosis 1. symptoms The symptoms of newborn infants are not obvious. If the mother is careful, she may find that the affected limbs are short, the skin pattern of the inner thighs is asymmetrical, and the thighs cannot be separated when urinating, which is especially obvious when they are bilaterally dislocated, and sometimes a popping sound can be heard, which leads to consultation. Most of the children learn to walk later, with limp and unstable gait, and only then draw the attention of parents and seek medical attention. After growing up, there is easy to lack and low back and hip pain, secondary to the occurrence of traumatic arthritis at the acetabulum, the pain gradually worsens and walking is difficult. 2. Clinical examination 1) Neonatal examination (1) Appearance and skin pattern The skin folds on the inner thigh of the affected side become deeper and increase, and the hip folds become higher. The affected limb may be shortened and mildly externally rotated. (2) Femoral artery pulsation The lining of the femoral head to the femoral artery is lost after dislocation and the pulsation is diminished. (3) Allis sign or Galeazzi sign The child is lying supine with the hip and knee flexed, legs together and both feet on the bed, and the affected knee is lower than the healthy knee. (4) Abduction test In normal infants, when the hip and knee are flexed and abducted, both thighs can be flat against the bed, but in hip dislocation, it is limited and the adductor muscle is tense. (5) Ortolani test and Barlow test The examiner holds both lower limbs of the child with both hands, with the thumbs on the inner thighs and the other fingers on the greater trochanter of the femur. Firstly, keep both hips and knees flexed at 90°, then gently abduct both hips and push the femoral greater trochanter with the fingers to the front, at this time the examiner can feel the popping sound when the femoral head slides into the acetabulum, which means the Ortolani test is positive. The examiner can feel another popping sound, indicating that the femoral head is slipping out of the acetabulum, which is a positive Barlow’s sign. 3. Examination of older children (1) Posture In bilateral dislocation, the perineum is widened, the hips are shrugged back, the anterior protrusion of the lumbar spine is increased, and the abdomen is protruded. (2) Limp – unilateral; bilateral – “duck-like gait”, swaying walking (3) Sleeve test (telescope sign, cylinder-like test) When the pelvis is fixed, the affected limb is tucked in, and the hip joint is pulled and pushed, there is a feeling of up and down movement of the femoral head as positive. (4) Trendelenburg test (single leg standing leg lift test) When the affected leg is standing and lifting the healthy leg, the hip on the healthy side drops and the pelvis tilts toward the healthy side is positive. (5) The anterior superior iliac spine is connected to the sciatic tuberosity as the Nelaton line. The apex of the greater trochanter of the femur is higher than this line during dislocation. 4.X-ray examination and CT examination The main manifestations of X-ray examination: femoral head epiphysis The femoral head epiphysis is small and appears late or the femoral head is displaced upward. The acetabular angle is enlarged (normal is about 22°), and the acetabulum is shallow. Perkins’ square (acetabular square) Perkins’ square is formed by drawing a line along the lateral edge of the two acetabulae and perpendicular to the horizontal axis of the yaw line (H line), which is a line connecting the cartilage of the two acetabulae in three directions. The normal femoral head epiphysis should be in the inner lower image of the square. In hip dislocation, the femoral head epiphysis is displaced outward and upward and is located outside and above the Perkins’ square. In recent years, with the advancement of technology and the joint efforts of clinicians and researchers, some new examinations have been applied to the examination of this disease and the determination of treatment plan. 3D reconstruction of CT has more intuitively and comprehensively evaluated the pathological morphology of dislocated hip and established the possibility of individualization for the determination of treatment plan. 5.Diagnosis Based on the above symptoms, clinical examination and X-ray performance, the diagnosis of hip dislocation is not difficult. Especially after the child starts to walk and develops limp or swaying gait, it is easy for parents to pay attention and come to the clinic to confirm the diagnosis, but it is already too late for diagnosis. The key to prognosis is early diagnosis and timely treatment. The earlier the detection and treatment, the simpler the treatment method and the better the treatment effect; on the contrary, if the diagnosis and treatment are delayed, the consequences will be endless. If diagnosed and treated in the neonatal period, the method is simple and the efficacy is most desirable, and later X-rays can be completely normal; most of the diagnosis and treatment within 1 year of age can be expected to cure, which shows the importance of early diagnosis. The current problem is that the level of diagnosis of hip dislocation in newborns is not high, and China has not yet established a universal screening and registration system. Orthopedic surgeons and obstetricians should be required to be familiar with the above-mentioned neonatal examination methods and be able to go to the neonatal unit for universal examination of newborns to confirm the diagnosis as early as possible.