The best time to treat pediatric hip dislocation is from birth to within 6 months of age. During this period, if infants are found to have some of the following phenomena, they should be taken seriously and promptly go to the pediatric orthopedic department for examination: 1. Asymmetry in the height of skin folds on the hip, groin or thigh, or asymmetry in the number of strips. 2, the infant bilateral lower limb activity imbalance, one side of the lower limb activity less, the other side of the lower limb activity more. Or one side of the lower limb strokes powerfully, while the other side of the lower limb strokes little power. 3.The appearance of the two lower limbs is not symmetrical, the length of the thighs are not the same thickness. 4.The appearance of the thighs are shortened and the lower limbs are externally rotated, i.e. the toes are obviously outward. 5.When moving the lower limbs, a popping sound is felt in the hip joint. 6.When the lower limb is straightened or flexed, the hip joint cannot be fully restricted, etc. These phenomena are more obvious when one side of the hip is dislocated, but may be less obvious when both sides are dislocated. When the child is between 6 and 18 months of age, there are some changes in the clinical presentation. For example, the femoral head has prolapsed out of the acetabulum and it is no longer possible to incorporate the femoral head into the acetabulum by simply abducting the hip joint. Several other clinical manifestations become more evident, the first and most reliable sign being the limitation of abduction of the dislocated hip due to contracture of the adductor muscle groups. However, in cases of hip dislocation there may be no limitation of abduction, and in infants and children with normal hips there may be limitation of hip abduction. When the femoral head is dislocated not only laterally but also upward, it causes relative shortening of the femur on the dislocated side, which is manifested by a significant shortening of the thigh on the dislocated side, with a positive Allis or Galeazzi sign. In children entering walking age, claudication is often the only complaint of the child. A bilateral dislocation presents with a “duck stance” with a pronounced posterior protrusion of the hips and a wobbly gait. These symptoms will gradually worsen with age. However, for children who do not have anatomical dislocation of the hip joint, that is, the femoral head is still located in the acetabulum, only the acetabulum is shallow and the slope is large, “acetabular dysplasia, subluxation”, the above symptoms are not obvious. Ultrasound examination of the hip joint is the preferred method for infants within 3 months of birth. Ultrasound hip examination technology for the diagnosis of pediatric hip dislocation has been carried out in many countries and regions around the world, promoting early detection and early treatment of hip dislocation and effectively reducing the incidence of late stage and complications of the disease. Ultrasound has the property of penetrating cartilage without radiographic damage, which is especially suitable for newborns and small infants less than 3 months old before ossification of the femoral head has occurred, and allows dynamic observation. As the ossification center of the femoral head forms and increases in size, the ability of ultrasound to penetrate the femoral head is obscured and its ability to show the acetabular floor decreases. In general, ultrasound examination of the hip joint is no longer appropriate for infants older than 6 months of age. Although ultrasound hip examination is a sensitive, accurate, non-invasive and easy to perform method, many studies have concluded that it is highly subjective and may result in false positives, so a comprehensive judgment is needed in conjunction with a careful clinical examination by a pediatric orthopedic surgeon. Routine clinical examinations include the Ortolani test and the Barlow test. MRI can also be performed if necessary, but it is not a routine test due to the high cost of MRI. Hip radiographs should be routinely taken in children over 3 months of age to clarify the diagnosis. From the perspective of improving national health and reducing infant disability rate, it is very meaningful to fully implement hip ultrasound screening for newborn infants. What is the timing and effect of treatment for hip dislocation in children? The treatment principle of hip dislocation in children is to achieve and maintain concentric repositioning of the femoral head in the acetabulum without affecting or minimizing the blood supply to the femoral epiphysis, to stimulate the development of the acetabulum and achieve as much joint surface coverage as possible, and to strive to make the dislocated or dysplastic hip grow and develop towards the most normal anatomical relationship possible. Overall, early diagnosis creates the conditions for early treatment, which in turn allows for rapid correction of pathologic changes in the hip joint. The younger the patient, the less severe the pathologic changes and the better the outcome. In the vast majority of cases, early diagnosis within the first few months of life can lead to complete success of conservative treatment. The treatment of hip dislocation in children is divided into two main categories: conservative treatment and surgical treatment. The choice of treatment method depends on the age of the child, the severity of the lesion, and whether the child is walking and weight-bearing. Conservative treatment is suitable for children under 18 months of age. Conservative treatment should follow the following principles: 1. Choose a posture that maintains the stability of the hip joint. 2.Choose different fixation methods according to the age. 3. Maintain a certain period of time after repositioning to encourage the development of the acetabulum and femoral head. Conservative treatment methods are: 1, Pavlik sling: is the most widely used method in conservative treatment, mainly suitable for infants under 6 months Pavlik retainer should be worn around the clock until hip stability is obtained, i.e. Balow test and Ortolani test negative, which usually takes 3 to 4 months. Thereafter, it can be removed for 2 hours per day, and the removal time can be extended by a factor of 1 every 2 to 4 weeks until it is worn only at night and continues until radiographs show a normal hip joint. The success rate of neonatal resurfacing has been reported in the literature to be over 90%, and over 85% for small infants less than 6 months of age. Age over 6 months is generally not suitable for Pavlik’s sling treatment. 2.Traction repositioning: It is suitable for children under 6 months of age with complete dislocation of the hip joint and heavy contracture of the adductor muscle. Through continuous traction, the hip joint is gradually abducted, and the femoral head is naturally repositioned. The biggest advantage of traction repositioning is that the head of the femur is gradually repositioned and ischemic necrosis is avoided. The disadvantage is that the hospitalization period is long, the traction process is difficult to take care of, and the skin damage caused by traction may hinder the treatment. 3.Manipulative repositioning: suitable for the treatment of infants and children aged from 6 months to 18 months. A standard treatment plan includes adequate preoperative traction, adductor excision and closed repositioning. Closed repositioning should be performed under general anesthesia, and the technique should be gentle. Once the repositioning fails, surgical treatment should be used instead, and repeated repositioning should be avoided to prevent damage to the femoral head. After manual repositioning, herringbone plaster fixation is used in the safety angle. The safety angle helps to prevent ischemic necrosis of the femoral head. Plaster fixation usually needs to be maintained for at least 3 months to obtain stability of the hip joint, after which the treatment can be maintained with an abduction brace or cast for 6 months or longer. During this period, the development of the hip joint is promoted through mutual stimulation of the femoral head and acetabulum, and the coverage of the femoral head by the acetabulum is increased. Surgical treatment is appropriate for cases aged 18 months or older or where conservative treatment has failed. The best time for surgical treatment is within 4 years of age. The surgical approach usually consists of two aspects: first, incision and repositioning, removing soft tissue structures that prevent repositioning and achieving concentric repositioning of the femoral head. The second is to correct the deformity of the acetabulum and proximal femur by means of pelvic and femoral osteotomy. In the treatment of hip dislocation in children, there is a risk of femoral head necrosis, re-dislocation, or residual deformity with any of the treatment methods. In a sense, the treatment of femoral head necrosis is more difficult than the treatment of hip dislocation itself, so this should always be thought of in the treatment of pediatric hip dislocation to avoid femoral head necrosis as much as possible. For example, the age of conservative treatment should be strictly controlled within 18 months, and closed repositioning should be performed under general anesthesia, with gentle techniques, and violent repositioning, repositioning without general anesthesia and repeated repositioning should be avoided. External fixation with plaster or brace must leave enough “safety angle”. During the surgical treatment, we should strive to obtain head and socket matching and coordination, and avoid damaging the blood supply to the femoral head, etc. If conservative treatment fails and the femoral head is dislocated or deformed, surgical treatment is still possible, but if surgical treatment fails or leaves a more obvious participation deformity, although re-operation is still possible, the chance of femoral head necrosis is much higher and the result is not satisfactory.