The incidence of this disease is affected by many factors, such as geography, living habits, ethnicity, etc., its incidence rate is very relevant, in northern Italy, France and southern Germany, the incidence rate is higher, Mckeown et al. 1960 reported that the incidence rate of Birmingham, England is 0.7%, and Sweden is 1%, in Japan and the American Indian tribes incidence rate is also higher. And Hodgson that the incidence of our China is very low, he mainly refers to the southern region of China, because of the habit of bringing children is two hip separation; knee flexion, because this baby position can correct the hip dislocation, and in fact, in different parts of our country the incidence rate is not consistent, but the lack of complete statistical data. But the incidence rate is not too low. And in the African region, the incidence rate is the lowest region in the world. Our data is roughly: the incidence rate of surviving children is 1%. The left side is more than the right side is about 10:1, bilateral dislocation to the right side is more serious. The incidence of congenital hip dislocation is higher in first-born babies, especially in breech babies, and about 16% of breech babies suffer from congenital hip dislocation. Different regions have different incidence rates, the incidence rate in northern China is higher than that in the south, the incidence rate in northern China is 3.8%, in eastern China is 1.1%, and in southern China is 0.7%. Etiology The etiology of congenital hip dislocation has not been completely clarified so far. Of course, multiple deformities attached to the hip dislocation should belong to the congenital deformity. In general, in recent years, most scholars believe that the etiology is not a single. This means that there are many factors to participate in order to cause this disease. (A) genetic factors undeniable fact that this disease has a clear family history, especially in twin babies more obvious, the incidence of this disease in the patient’s family can be as high as 20 ~ 30%, and more common in sisters. The same disease can occur in sisters with three types of hip dislocation and dysplasia. If detailed, early examination and X-ray diagnosis are not carried out, except for the first type, the latter two types can often be missed and the hip joint has been completely normal by the time the patient reaches the age of 7 or 8 years. (B) Ligament laxity factor In recent years, more and more reports have proved that laxity of joint ligaments is an important factor. In animal experiments Smith will be puppy’s joint capsule, round ligament excision, produce hip dislocation phenomenon of high percentage, clinically Andren pointed out that the X-ray film in the pubic symphysis separation in hip dislocation cases for the normal infants twice, he thinks that this is the mother in the process of production needs a lot of endocrine ligament laxity, excessive endocrine changes is caused by hip dislocation is an important factor. Meanwhile, Andren, Borglin found changes in urinary estrone (Estrone) estradiol 17β (Estradil) excretion compared with normal infants in newborn hip dislocation cases within 3 days. However, Thieme utilized 16 sick infants compared to 19 normal infants and when measured month by month, statistically processed found no difference. Therefore, the theory that endocrine changes cause ligamentous laxity cannot yet be established. (C) Position and mechanical factors Hip dislocation cases in breech births have been reported to be as high as 16-30% of cases, and breech births in normal births accounted for only 3Wikinson (1963) fixed young children’s hips in flexion, external rotation, and knee extension, and gave estrogen and progesterone. Hip dislocation deformity can occur. Postnatal position has also been suggested as a factor in this condition. For example, the high incidence in Sweden and American Indians is due to the swaddling position applied to infants. Pathologic changes The pathologic changes of congenital hip dislocation include two parts: (1) Bone changes Hip dysplasia is the fundamental change, this change includes the acetabulum, pelvis, femoral head, femoral neck, and in severe cases, can also affect the spine. 1.Acetabular security Hip dislocation is normal in birth fashion, while there is a cut mark outside the upper outer edge of the acetabulum, with growth and development acetabulum gradually become narrow and shallow, triangular. The acetabular labrum is thickened, due to the constant extrusion of the femoral head can cause internal or external rotation, the acetabulum after the upper part of the femoral head due to the extrusion of the formation of false socket, acetabular anterior edge of the inner upper part of the often seen a defect. Acetabulum due to the absence of the femoral head of the role of modeling and dysplasia, the acetabulum gradually become smaller and shallower, the bottom of the acetabulum is full of fatty fibrous tissue, the round ligament is often thickened and hypertrophied after constant stretching to fill up the acetabulum. 2, the femoral head of newborns is deformed, the surface has a smooth cartilage surface, and then due to dislocation outside the acetabulum, the shape of the femoral head can gradually change, the head can become large or small, pointed cone or repair-shaped, the femoral head is often flattened at the place of the pressure on the femoral head. The epiphysis of the femoral head is delayed. Sometimes, strong and violent surgical reset is applied, because the acetabulum is not compatible with the femoral head, the pressure on the femoral head is too great, which can cause aseptic necrosis of the femoral head. 3.Femoral neck due to hip dislocation, the femoral neck generally becomes shorter and thicker, which is a cause of limb shortening. The anterior tilt angle of femoral neck becomes bigger, according to Caffey, the normal newborn’s anterior tilt angle is 25°, and then gradually reduced to between 5° and 15°, when the femoral head is moved outward, due to the role of the normal muscle force, rotating forward to the femoral head, the anterior tilt angle is increased, generally between 60° and 90°. If the femoral head can be reset early, the anteversion angle can be corrected gradually by itself. In particular, almost all of those who are reset within 1 year of age can return to normal. 4.Pelvis and spine dislocation on one side of the pelvis is often accompanied by dysplasia, the iliac flanks are more oblique, and the sciatic nodes are more separated. In both sides of the dislocation, the above lesions exist outside, the pelvis tilted forward and make the lumbar anterior protrusion arc increased, sometimes can appear scoliosis. (B) soft tissue changes This refers to all the soft tissues around the hip joint including skin, fascia, muscles, tendons, joint capsule, ligaments, and intra-articular discoidal cartilage of the hip joint, of which intra-articular discoidal cartilage, joint capsule and tendons are the most important. 1, disk cartilage (Limbus) normal 14.8mm embryo, hip joint is a pile of mesenchymal cells, after the acetabulum and the femoral head of the gap between the mesenchymal cells began to absorb the middle of the block to the edge of the only remaining. At 25 mm the joint capsule and the acetabular annular ligament (glenoid labrium) appear. Any mechanical stimulus at the main stage of acetabular formation produces a normal mesenchymal resorption that stops and discoidal cartilage appears. In fact, discoidal cartilage resorption insufficiency is seen in the posterior and superior portion of the acetabulum, where it proliferates and enlarges so that the head of the femur does not point directly to the center of the acetabulum. Leveurf and Somerville believe that this is the main cause of hip dislocation and the key to reset. In children over 3 years of age who cannot get the femoral head into the acetabulum after traction in surgery, most often have hypertrophied discoid cartilage. This kind of cartilage is exactly like the disk meniscus in the knee joint, which covers a large part of the joint surface so that the femoral head and acetabulum can not be contacted, resulting in the development of dysplasia of the two. 2, the joint capsule The normal hip joint capsule is a layer of fibrous tissue 0.5 ~ 1.0mm thick and thin. Since the head of the femur out of the acetabulum to the upward displacement of children after weight-bearing, the joint capsule by pulling and growth and thickening sometimes can be as large as 2 to 3 mm, long-term pulling so that the joint capsule and the acetabulum above the iliac wing adhesion, coupled with the round ligament, disk cartilage and the joint capsule between the adhesion, the formation of a whole piece of connective tissue, impede the head of the femur to enter the acetabulum. The joint capsule is gourd-shaped with a narrow neck in the later stages, and the femoral head itself cannot pass through. The iliopsoas tendon passes in front of the joint capsule, sometimes in very early stages with a notch that prevents the femoral head from resetting. The joint capsule attaches below the femoral head instead of attaching between the greater and lesser trochanters. Normal round ligament connects the central recess of the femoral head with the inner and lower part of the acetabulum. In hip dislocation cases, the joint capsule and the round ligament are pulled at the same time and thickened, and the round ligament and the joint capsule are adhered together and disappear over time. The central artery in the round ligament is also thickened and prematurely occluded due to the pulling position. 4, muscle As the femoral head upward displacement, all from the pelvis along the femur downward walking most of the muscles are shortening, including the adductor muscle and iliopsoas muscle is more obvious, and many tendons have fibrous degeneration. The posterior muscle groups, including the gluteal muscles, are also shortened, muscle strength is weakened, affecting the stability of the joints, appearing wobbly gait. 5, fascia Although the lateral muscle group is theoretically lengthened, but the gluteal fascia can be seen to have contracture, the patient can not be inwardly retracted, this fascia have fibrous tissue hyperplasia, serious collagen degeneration. Fascial laxity must be performed during surgery to ensure repositioning. Clinical manifestations (1) neonatal and infantile manifestations: ① Symptoms: A, joint mobility disorders: the affected limb is often flexed, the activity is poorer than the healthy side, the stirrup force is weaker than the other side, the hip joint abduction is limited. B. Shortening of the affected limb: the femoral head of the affected side is dislocated backward and upward, and the corresponding shortening of the lower limb is common. C, skin lines and changes in the perineum: asymmetry of the skin folds on the buttocks and inner thighs, the skin lines on the affected side are deeper than those on the healthy side, the number increases, the labia majora of female infants are asymmetrical, and the perineum is widened. ② Examination: A. Ortolani test and Barlow test: for congenital hip dislocation between birth and 3 months of age. It was first proposed by Ortolani in 1935 and improved by Barlow.Ortolani’s method is to flex the child’s knees and hips to 90°, the examiner puts the thumb on the inner thigh of the child, and the forefinger and middle finger on the greater trochanter, and gradually abducts and externally rotates the thigh. If there is dislocation, you can feel the femoral head embedded in the acetabular rim, which produces a slight resistance to abduction, and then lift the greater trochanter with the middle finger of the index finger, the thumb can feel the femoral head sliding into the acetabulum when the popping, i.e., Ortolani’s test is positive. barlow test is the reverse of the operation of Ortolani’s test, the examiner, so that the patient’s thighs passive inwardly rotated and the thumb outwardly above the pressure on the femur rotor. A popping motion can be felt again. B. Allis’s sign (Galezzi’s sign): make the newborn lie down and bend the knee 85 ° ~ 90 ° legs together, the heels of the feet are aligned, such as this disease can be seen in the two knees are not equal. This is caused by upward displacement of the femur on the affected side. C. Sleeve test: make the child lying down, the affected side of the hip and knee joints are flexed 90 °, the examiner holds the distal femur and knee joint with one hand and presses the groin with the other hand, and if you feel that the greater trochanter is moving up and down when you are lifting and pushing the knee of the affected limb, it is positive for the sleeve test. D. Hip and knee flexion and abduction test: make the baby lying down, hip and knee flexion, the examiner holds the knee with both hands, thumb on the inside of the knee, the rest of the four fingers on the knee, the outside of the normal baby can generally abduct about 80 °, if only 50 ° ~ 60 ° abducted, it is positive, can only be abducted 40 ° ~ 50 ° for a strong positive. (2) Manifestations in early childhood: ① Symptoms: A. Limping gait: limping is often the only complaint of parents when pediatricians visit the clinic. One side of the dislocation manifested as claudication; bilateral dislocation is manifested as “duck step”, the child’s buttocks obviously protruded backward lumbar anterior convexity increased. B, the affected limb shortening deformity: in addition to shortening at the same time there is internal deformity. ② check: A, Nelaton line: anterior superior iliac spine and sciatic tuberosity line, normally through the apex of the greater trochanter, known as the Nelaton line, hip dislocation, the greater trochanter above this line. B. Trende lenburg test: the child is asked to stand on one leg, the other leg as much as possible, flex the hip, flex the knee so that the foot off the ground, the normal standing on the contralateral side of the pelvis rises; hip dislocation of the femoral head can not hold the acetabulum, the gluteus medius muscle weakness, so that the contralateral side of the pelvis falls. Observation from behind is particularly clear, called Trendelenburg test positive, is a sign of hip instability. 2.Classification (1)Classification according to the relationship between the femoral head and acetabulum: Generally, it can be classified into the following 3 types: ①Congenital dysplasia: the femoral head is only slightly shifted outward, Shenton’s line is basically normal, but the CE angle can be reduced, and the acetabulum becomes shallow, which is referred to by Dunn as congenital hip subluxation grade I. ②Congenital subluxation: the femoral head is only slightly shifted outward. ② congenital subluxation: the head of the femur is displaced outward and upward, but still forms a joint with the lateral part of the acetabulum, Shenton’s line is discontinuous, CE angle is less than 20°, and the acetabulum becomes shallow, which belongs to Dunn’s classification of grade II. (iii) Congenital complete dislocation: the femoral head is completely outside the true acetabulum, forming an articulation with the lateral aspect of the ilium, gradually forming a false acetabulum, and the original joint capsule is embedded between the femoral head and the ilium, which belongs to Dunn Classification Grade III. (2) Classification according to the degree of dislocation: Sun Zaikang refers to Zionts’ standard and classifies it into 4 degrees as follows: ①Ⅰ degree dislocation: the epiphyseal nucleus of the femoral head is located below the Y line, and outside of the vertical line of the outer upper edge of the acetabulum. ② Ⅱ degree dislocation: the epiphyseal nucleus of the femoral head is located between the Y line and the parallel line of the upper edge of the acetabulum of the Y line. (iii) Third degree dislocation: the epiphyseal nucleus of the femoral head is located at the height of the parallel line of the superior acetabular rim. (iv) Degree IV dislocation: the epiphyseal nucleus of the femoral head is located above the parallel line of the superior margin of the socket, and there is pseudo-socket formation. Complications: Ischemic necrosis of the femoral head can occur regardless of conservative or surgical treatment, and re-dislocation and joint stiffness can occur after surgical treatment, which need to be prevented during treatment. 1.Ischemic necrosis of femoral head This is a medical complication, mainly caused by mechanical pressure to arterial ischemia.Salter put forward 5 diagnostic criteria: (1) 1 year after the reset, the epiphyseal nucleus of the femoral head still does not appear. (2) Stagnant growth of the existing epiphyseal nucleus 1 year after reset (3) Widening of the neck of the femur 1 year after reset. (4) The femoral head becomes flattened with increased density or fragmentation occurs (5) The residual deformity of the femoral head includes head flattening and flattening, flat hip hip inversion, short and wide femoral neck, etc. 2. Post-operative re-dislocation, although the incidence of post-operative re-dislocation is not high, once it occurs, it has a poor prognosis, and necrosis of the femoral head and stiffness of the joints can occur, so every effort should be made to prevent it. The main reason is that the joint capsule tightening is not ideal, which is the most common reason; followed by the anterior tilt angle is too large and not given correction; there is also the asymmetry of the head and socket is not well dealt with, etc., and the reason should be strengthened to prevent it. Once occurred should, early surgical treatment. 3, hip joint movement limitation or stiffness, this complication is more common. The older the patient is, the higher the incidence, the higher the position of the dislocated femoral head is, the heavier the contracture around the hip joint is, if not corrected, it is very easy to occur hip joint movement limitation or stiffness, especially for those who apply the hip herringbone plaster cast fixation after the operation, it is more likely to happen, it should be strengthened to strengthen the early postoperative joint function exercise by taking the hip abduction plaster cast brace fixation, it should be sitting up and practicing the activities in the week after the operation, it is possible to fix it without the plaster cast, it should be used for Continuous passive movement (CPM) for joint functional exercise.