After birth to within 6 months is the best period for the treatment of pediatric hip dislocation, during this period of time, if the infant is found to have some of the following phenomena, should be taken seriously and promptly go to the hospital with pediatric orthopedics to check: ① hip, groin or thighs behind the knee joint skin fold height asymmetry, or the number of asymmetrical; ② infants bilateral lower limb activity imbalance, one side of the lower limb activity less, the other side of the lower limb activity or one side of the lower limb stirrup powerful, the other side of the lower limb stirrup power is small; ③ two lower limbs appearance is not symmetrical, the length of the thigh thickness is not the same; ④ thigh appearance has shortening, and the lower limb external rotation, that is, the toe is obviously outward; ⑤ activities of the lower limb, feel the hip joint popping sound; ⑥ lower limb extension or flexion, the hip joint can not be fully restricted, and so on. These phenomena are more obvious when one hip joint is dislocated, but less obvious when both hips 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 group. 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, lameness is often the only complaint in children presenting to the clinic. The limp is present in the case of unilateral dislocation, while bilateral dislocations show a “duck stance” with a pronounced posterior protrusion of the hips and a wobbly gait. This wobbly gait is often overlooked by parents. With increasing age, these symptoms will gradually worsen. 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”, the above symptoms are not obvious. Ultrasound examination of the hip joint is the preferred method for infants within 6 months of birth, and the diagnosis of pediatric hip dislocation has been carried out in many countries and regions around the world, promoting the early detection and treatment of hip dislocation and effectively reducing the late incidence of the disease and the incidence of complications. Ultrasound has the property of penetrating cartilage without radiographic damage, which is especially suitable for newborns and small infants under 6 months of age 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 must be made in conjunction with a careful clinical examination by a pediatric orthopedic surgeon. Routine clinical examinations include the Ortolani test and the Barlow test. MRI may also be performed if necessary, but it cannot be used as a routine test because of its high cost, and hip radiographs should be routinely taken in children over 6 months of age to clarify the diagnosis. It should be emphasized here that the human hip joint is a three-dimensional structure, and conversion into two-dimensional X-ray and ultrasound images is affected by the accuracy of the instruments, the position of the examination, the quality of the images and the doctor’s ability to interpret the images, etc. It must be combined with clinical examination to make a clear 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, and we hope that newborn hip ultrasound screening can be gradually incorporated into the routine examination program in areas where conditions are available. Timing and effects of treatment for pediatric hip dislocation After the diagnosis of pediatric hip dislocation is clear, how should it be treated? When is the best time for treatment? What is the effect of treatment for pediatric hip dislocation? The treatment principle of pediatric hip dislocation is to achieve and maintain the concentric reset of the femoral head in the acetabulum without affecting or minimizing the blood supply to the epiphysis of the femoral head, stimulate the development of the acetabulum and achieve as much joint surface coverage as possible, and strive to make the dislocated or dysplastic hip joint 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 pediatric hip dislocation is divided into two main categories: conservative treatment and surgical treatment. The choice of treatment method depends on various factors such as 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 promote the development of the acetabulum and femoral head. The methods of conservative treatment are: (1) Pavlik sling: it 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. The Pavlik sling is generally not suitable for infants older than 6 months of age. (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 muscles. 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 resetting: suitable for the treatment of infants and children aged 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, with gentle maneuvers. Once repositioning fails, surgical treatment should be used instead, and repeated repositioning should be avoided to prevent damage to the femoral head. After manual repositioning, a human position cast is used in the safety angle. The safety angle helps to prevent ischemic necrosis of the femoral head. Plaster fixation is usually maintained for at least 3 months to obtain stability of the hip joint, after which 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 to remove the soft tissue structures that prevent repositioning and achieve concentric repositioning of the femoral head; second, correction of the deformity of the acetabulum and proximal femur by means of pelvic and femoral osteotomy. In the treatment of pediatric hip dislocation, necrosis of the femoral head, re-dislocation, or residual deformity may occur 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; 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 in plaster or brace should be left with sufficient “safety angle”; surgical treatment should strive to obtain head and socket matching and coordination to avoid damaging the blood supply to the femoral head, etc. The surgical treatment should strive to obtain cephalosubstance matching and coordination to 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 if there is a more obvious deformity, the chances of femoral head necrosis are much higher and the results are not satisfactory. From the above rough introduction of pediatric hip dislocation, we can see that the pathology of pediatric hip dislocation is quite complex, and its diagnosis and treatment are very specialized, so it is difficult for doctors without specialized training in pediatric orthopedics and without a good understanding of pediatric developmental hip dislocation to take charge of it.