Developmental dislocation of the hip (DDH) used to be called congenital dislocation of the hip (CDH) as one of the common extremity deformities. In 1992, the North American Academy of Pediatric Orthopaedic Surgery officially renamed it as a congenital dislocation, and concluded that in addition to congenital factors, acquired factors play a more important role, i.e., most children are not born with the dislocation, but develop it gradually after birth with growth and development, and it can be prevented. Developmental hip dislocation is a collective term that includes all hip dysplasia in children, including congenital dislocation, neonatal and infantile hip dysplasia (easy dislocation, subluxation, reducible dislocation and irreducible dislocation). Clinical manifestations of developmental hip dislocation I. Infancy (pre-standing) 1. Appearance and skin wrinkles: In unilateral hip dislocation, the affected side of the thigh, calf and labia majora are asymmetrical with the opposite side, the skin folds of the inner thigh or the country fossa are added more and deepened or asymmetrical, and the perineum is widened. However, clinically, the asymmetry of skin wrinkles is not specific and has little value for diagnosis; in fact, 50% of infants and children have asymmetrical skin wrinkles. 2. Restricted joint movement: The affected child has temporary joint dysfunction or the joints are in a certain fixed position. Most of the children’s limbs are flexed and afraid to straighten, and the activity is reduced compared with the healthy side. A few children have a history of crying when pulling the affected limbs in external rotation, external booth or cross position. 3, limb shortening: unilateral dislocation is common when the affected side of the lower limb shortening, clinical Allis sign or Galeazzi sign can be positive: the child lying flat, flexion 90 °, two feet flat on the bed, two ankles together can be seen two knee high and low uneven. This is due to the upward displacement of the femur after hip dislocation. 4.Barlow test (ejection test): It is a reliable method to diagnose hip dysplasia and hip instability. The child lies on his back, the examiner faces the child, flexes the hip and knee by 90°, puts the thumb on the inner thigh at the small rotor with pressure, pushes the femoral head upward, and feels the femoral head is dislodged from the socket to the outer socket, which is positive for Barlow’s sign. 5, Ortolani test (pop-in test): the opposite of the Barlow test, thumb on the inner thigh, the rest of the limbs are at the greater trochanter, to the lower extremity pressure abduction, can feel the femoral head from outside the socket to slide into the socket bounce, then the Ortolani sign positive. 6.Abduction test: This method is an important tool for neonatal census. The child is lying down, flexing the hip and knee at 90° each, and holding both knees with both hands while abducting and externally rotating, normal abduction in infants is generally about 70°~80°, if abduction is below 50°~60°, it is positive. Clinical practice proves that more than 90% of the affected hip dislocation abduction test is positive. In addition to the negative Barlow test and Ortolani test, there are other clinical manifestations of developmental hip dislocation in infancy and early childhood. In addition, there are other clinical manifestations. 1. Obvious shortening of the affected limb, limited abduction, and protrusion of the greater trochanter outward. 2. Abnormal gait: limp in unilateral dislocation; duck gait in bilateral dislocation, and posterior shrugging of the arms and forward convexity of the waist. 3. Positive Trendelenburg test: stand on one leg, bend the other leg at the hip and knee, and keep the foot off the ground. In normal standing, the contralateral pelvis is tilted upward; in dislocation, because the femoral head does not hold the acetabulum, the gluteus medius muscle is weak and the contralateral pelvis is tilted downward, which is obvious when observed from behind. Treatment of developmental hip dislocation The key to the prognosis of developmental hip dislocation lies in early diagnosis and early treatment. The earlier the treatment, the better the results. As the age increases, the more serious the pathological changes are, the worse the treatment effect is. Generally, there are conservative treatment and surgical treatment. At present, it is considered that conservative treatment is appropriate up to 3 years of age (preferably up to 2 years of age, the younger the age, the better the results). For children under 6 months of age with mild dislocation, treatment with a dressing girdle or Pavlik sling can be done at 6-9 months. For children older than 6 months or with dislocations of II° or more within 6 months of age, traction repositioning or direct repositioning under anesthesia (with or without severing of the adductor muscle) and bracing or plaster fixation are often used, which usually takes 6 months to 1 year. The efficacy of conservative treatment decreases with age and the degree of dislocation, and some children are left with residual deformity after the end of conservative treatment, and some children still need additional surgery to achieve the root cause as much as possible. Surgery is required for children over 3 years of age or if conservative treatment fails.