Developmental dysplasia of the acetabulum (DDH) is a common developmental disorder in adolescents, with a prevalence of approximately 1-1.2/1000, whose root causes are already present in infancy and childhood, and which remain due to undetected or incomplete treatment. Its main pathologic features are shallow acetabulum and outward displacement of the femoral head. In early adulthood, there is a link between DDH and secondary osteoarthritis of the hip. Dysplasia of the acetabulum is present in approximately 48% of those patients who require total hip replacement to treat their hip osteoarthritis. If left untreated early, 25-50% of patients will develop osteoarthritis of the hip after the age of 50. Therefore, early detection and treatment is especially critical to delay or even prevent the progression to osteoarthritis of the hip. Hip preservation treatment has been agreed by international joint surgeons, especially for young patients, if surgery can be actively taken to improve the relationship between the head and the socket of the hip joint, alleviate the symptoms, preserve the original joint as much as possible, delay the time of artificial joint replacement, and avoid the pain and economic burden brought by early joint revision. I. Disease Diagnosis (I) Clinical Symptoms Acetabular dysplasia most often appears between the ages of 20-40 years old. In the early stage, the symptoms are mostly fatigue in the hip, which can also occur in other parts of the body, such as the groin area, the front of the thigh and the buttocks, with pressure and rotation pain in the hip joint, and normal or abnormal activities. In the middle and late stages, the clinical symptoms are mostly aggravation of hip joint pain, followed by claudication and resting pain; joint subluxation to short limbs and more, with the gradual aggravation of osteoarthritis to joint mobility limitation. (B) X-ray performance 1, standing position pelvis X-ray: acetabulum development shallow small, acetabulum to the femoral head of the coverage area is reduced, the head of the femoral head of the weight-bearing point of displacement, hip joint medial gap widening, joint dislocation; acetabulum to the pelvis tilt is too large, weight-bearing area becomes shorter; acetabular fixed lateral labrum bone dysplasia; secondary osteoarthritis manifestation. Even the joint dislocation, the femoral head is located above the acetabulum, squeezing the ilium to form a false socket. 2, for acetabular X-ray measurement and significance (1) CE angle: sub-femoral head center (C) to the upper edge of the outer acetabulum (E) draw a line, another through the center of the femoral head for a vertical line, the angle between the two lines for CE angle, if the adult CE angle <20 °, 13-17 years old teenagers ce angle <15 ° for acetabular dysplasia. (2) Acetabular angle: take the line connecting the lower edge of the tear point on both sides, and then make a line connecting the outer edge of the tear point and the upper edge of the acetabulum, the angle formed by the two, the angle >45° is acetabular dysplasia. (3) Acetabular index: normal (27.56±4.73)°, <20° is abnormal. (4) Acetabular angle: normal is (38.78±2.56)°, >20° is abnormal. (5) Scalloped angle of the white line of the acetabular cap: the angle formed by the straight line from the center of the femoral head to the two ends of the white line of the acetabular cap is scalloped angle, which is acetabular dysplasia. (6) Acetabular depth: take the line from the upper outer edge of the acetabulum to the upper angle of the pubic symphysis on the same side, the vertical distance from the deepest point of the acetabulum to this line indicates the depth of the acetabulum, <9mm for acetabular dysplasia; (7) ACM angle: from the upper edge of the acetabulum (point A) and the lower edge of the line of the mid-point (point M) to the center of the acetabulum as a perpendicular line, intersected at the acetabulum (point C), the angle formed by the AC and CM lines is the angle of the ACM. The angle formed by the AC line and the CM line is the ACM angle, and >50° is abnormal. 3, acetabular dysplasia CT manifestation: acetabular morphology is irregular, acetabular fossa is shallow, acetabular rim dysplasia, with acetabular parietal lip and anterior lip dysplasia is the most common. In the case of parietal lip dysplasia, the CT cross section of the top of the hip shows that all or part of the femoral head is bare outside the socket, and the CT shows the so-called “bald head sign”, while the anterior and posterior labral dysplasia is characterized by short anterior and posterior labrums, shortening of the articulating surface, and reduction of inclusiveness of the femoral head, which is manifested by the “hand-held ball sign”. CT shows the “hand-on-ball sign”. (C) Diagnostic criteria In the above X-ray performance, (1)-(4) measurements can be used as the main diagnostic basis, (5)-(8) are the secondary diagnostic basis, and the imaging diagnostic criteria of acetabular dysplasia are as follows: 1, conform to more than 2 X-ray main diagnostic basis; 2, conform to 1 X-ray main diagnostic basis plus more than 2 secondary diagnostic basis; 3, conform to the diagnostic criteria of CT. Second, acetabular dysplasia staging 1, Severin staging: applicable to adolescent and adult patients. The staging according to the patient’s age group and the size of the CE angle will be divided into six phases of acetabular dysplasia, of which the I-IV period for different degrees of semi-dislocation, the V period for complete dislocation, the VI period for re-dislocation. 2.Crowe staging: Crowe staging is a staging method to determine the degree of dislocation of the femoral head, which is established based on the evaluation of the surgical results of artificial arthroplasty for hip dysplasia with different degrees of dislocation, and its classification is simple and easy to implement, but it cannot evaluate the details of the morphological changes of mild acetabular dysplasia. Specific measurements: the horizontal line through the lower edge of the tear drop was used as the reference line on the orthopantomograph of the hip joint, the vertical height of the femoral head was used as the percentage reference height, and the distance of the medial femoral head-neck junction from the horizontal reference line was measured. (1) Stage I: femoral head subluxation, the height of subluxation is <50% of the vertical height of the femoral head; (2) Stage II: femoral head subluxation, the height of subluxation is 50-75% of the vertical height of the femoral head; (3) Stage III: femoral head subluxation, the height of subluxation is 75-100% of the vertical height of the femoral head; (4) Stage IV: complete dislocation of the femoral head, subluxation height >100% of the vertical height of the femoral head. (4) Stage IV: complete dislocation of the femoral head, dislocation height >100% of the vertical height of the femoral head. Classification of femoral head and acetabular anastomosis: The degree of anastomosis between the femoral head and the acetabulum after hip dysplasia is of great value in the choice of treatment, judgment of surgical effect and evaluation of prognosis. (2) Good: the relationship between the weight-bearing surface of the acetabulum and the femoral head is not good, but the joint space is basically normal; (3) OK: the weight-bearing surface of the acetabulum and the femoral head are poorly coordinated, and part of the joint space is narrow; (4) Poor: the weight-bearing surface of the acetabulum and the femoral head are poorly coordinated, part of the joint space is obviously narrowed, and the articular cartilage is severely worn. Hip dysplasia treatment program The treatment of hip dysplasia aims to correct the deformity of the acetabulum and proximal femur, increase the weight-bearing area of the hip joint, restore the coverage of the acetabular hyaline cartilage, and rebuild the normal biomechanical relationship of the hip joint. A treated near-normal hip will improve hip function and slow the progression of osteoarthritis. In principle, the earlier the treatment, the better the outcome. It is generally accepted that the optimal age for osteotomies for hip dysplasia is 5-6 years of age in childhood, when the bone tissue has the best bioelasticity and molding capacity. However, the vast majority of patients do not notice hip symptoms and deformities until adulthood. Although the elasticity and remodeling capacity of bone decreases significantly in adulthood, osteotomies can still relieve hip pain and slow the progression of osteoarthritis. Therefore, hip preservation therapy for adult hip dysplasia patients must be emphasized in order to correct the deformity and slow or stop the progression of osteoarthritis in the hip before it develops or worsens. For those patients with late onset of symptoms and less severe deformity, conservative treatment should be adopted, and artificial joint replacement can be considered after the advanced stage of osteoarthritis. The treatment principle of adult hip dysplasia depends on the patient’s age, clinical symptoms, the severity of joint deformity, the alignment of the femoral head and acetabulum, and the severity of hip osteoarthritis. （Patients <40 years of age with hip pain, mild subluxation on X-ray, good femoral head-acetabular alignment on radiographs, normal femoral neck angle, and no obvious osteoarthritis or narrow joint space should be selected for reconstructive acetabular osteotomy that can restore the anatomical coverage of the acetabulum; for patients who meet the above criteria but have a significantly increased femoral neck angle and a narrow joint space, the treatment should include reconstructive acetabular osteotomy. For patients who meet the above criteria, but the femoral neck angle is obviously enlarged and the hip is inversion deformity, proximal endarticulation osteotomy can be chosen to correct the hip valgus deformity and to improve the coverage of the femoral head; For patients who meet the above criteria, but the X-ray radiographs of the femoral head and the acetabulum are poorly matched or the subluxation is more severe, and the alignment of the femoral head and the acetabulum does not improve in the radiographs of the abutments, the salvage pelvic osteotomies can be chosen with great caution, such as the Chiari pelvic osteotomy. For patients who meet the above conditions but are older than 40 years old, conservative treatment can be chosen, and artificial joint replacement can be performed when osteoarthritis is severe; for patients with total dislocation of the hip without pseudo-acetabulum formation and osteoarthritic changes, or patients with pseudo-acetabulum formation but no hip pain and osteoarthritis, it is recommended to disregard the consideration of artificial joint replacement; for patients with pseudo-acetabulum formation and severe osteoarthritis, artificial joint replacement can be chosen; for patients with total dislocation of the hip and serious osteoarthritis, it is recommended to choose the artificial joint replacement. For patients with total dislocation of the hip with pseudoacetabulum formation and severe osteoarthritis, artificial joint replacement can be chosen. (B) Osteotomy for acetabular reconstruction This type of surgery is mainly suitable for patients with mild hip subluxation, good relationship between femoral head and acetabulum, and not severe osteoarthritis of hip. Due to the complexity and trauma of this type of surgery, older patients are less tolerant of the surgery, and recovery is often unsatisfactory, so it is only suitable for patients <40 years of age. Acetabular rotational osteotomy and periacetabular osteotomy have the osteotomy surface around the acetabulum, better acetabular freedom after osteotomy, easy to move the osteotomy block, higher angle and accuracy of deformity correction after surgery, and are widely used in the clinic. The periacetabular osteotomy through the ilioinguinal approach is an effective procedure for the treatment of adult hip dysplasia. Patients can obtain reliable deformity correction and functional improvement, and the results of medium-term follow-up are satisfactory; periacetabular osteotomy is a biological solution to hip dysplasia, which can lead to the sclerosis and capsule around the acetabulum to become relieved, regeneration of the periacetabular bone, maintenance of the joint space, and slowing down the development of osteoarthritis. Correct surgical manipulation and accuracy of the corrected position of the acetabulum are the keys to a good outcome with periacetabular osteotomy. Indications of periacetabular osteotomy: hip pain, but the mobility of the joint is normal or basically normal; age should be under 40 years old; Crowe stage I mild dislocation on X-ray; femoral head deformation is not significant, and the correspondence between the acetabulum and the femoral head on the radiograph of the outer booth is good; osteoarthritis stage I, with a basically normal joint space (young patients with osteoarthritis stage II can still choose this kind of surgery). Contraindications for periacetabular osteotomy: young age, the acetabular epiphysis has not yet healed (relative contraindication); severe subluxation and dislocation of Crowe III and IV; obvious deformation of the femoral head on the X-ray film of the external booth, poor correspondence between the acetabulum and the femoral head, and prediction that the head-acetabular alignment is still unsatisfactory after the operation; severe osteoarthritis on the X-ray film, and a narrow joint space. Periacetabular osteotomy (PAO) was performed using the Smith-Peterson approach in the anterior aspect of the hip joint. That is, firstly, an incomplete osteotomy of the sciatic branch was made in the subacetabular groove above the anterior aspect of the sciatic branch, then a complete cut of the outer edge of the pubic bone was made, after which an iliac osteotomy was made in the upper edge of the acetabulum, and osteotomy was made at the level of the arcuate line turned to the posterior and inferior part of the inner wall of the acetabulum along the sciatic macrotomy, and finally, a complete peri-acetabular osteotomy was completed with the round of osteotomy of the sciatic branch. Afterwards, the osteotomy block is rotated according to the pre-surgical design requirements to achieve satisfactory coverage of the femoral head and stable fixation is done using screws. Advantages of periacetabular osteotomy are: 1, using a surgical access to complete all the surgery; 2, the osteotomy block free degree is good, the acetabular deformity can be corrected thoroughly, and the center of the femoral head can be prevented from migrating out of the center of the femoral head after the operation; 3, the blood circulation of the acetabulum is kept intact, and there is a small possibility of acetabular bone necrosis; 4, as the iliac bone parallel to the sciatic notch is still intact, the mechanical integrity of the pelvis can be preserved, and internal fixation is simple and reliable, and patients do not need to have any fixation afterwards. Because the mechanical integrity of the pelvis can be preserved and the internal fixation method is simple and reliable, the patient can walk on the ground without any external fixation; 5. The true pelvis has not been structurally damaged, and the birth canal of young female patients is not affected. (C) For patients with complex hip dysplasia, in addition to the poor coverage of the acetabulum on the femoral head, the deformity of the femoral head (big head deformity, flat deformity and other changes in the shape of the femoral head); deformity of the proximal end of the femur (change in the anterior tilt angle of the femoral neck, internal and external rotation of the hip, and elevation of the greater trochanter, etc.), if you take the simple rotational osteotomy of the peri-acetabular surgery can not completely correct the deformity, so that the effect of the surgery is not satisfactory. Therefore, it is necessary to carefully analyze other deformities of the hip joint on the basis of periacetabular rotational osteotomy, and determine the orthopedic strategy in combination with other surgical methods. Simple hip dysplasia, choose periacetabular osteotomy (PAO); patients with simple increased anterior tilt angle, choose proximal trochanteric rotational osteotomy (Dero-ITO) + femoral neck lengthening; 2. Hip dysplasia plate femur anterior tilt angle increased, choose PAO + proximal trochanteric rotational osteotomy (Dero-ITO); 3. Hip dysplasia with Hip external rotation deformity +/- abnormal anterior tilt angle of femoral neck, choose PAO + proximal femoral osteotomy (PFO); 4. Hip dysplasia with hip internal rotation deformity +/- abnormal anterior tilt angle of femur, choose PAO + PFO +/- femoral neck lengthening; 5. Hip dysplasia with labral injury, +/- femoral head cam-like impingement, choose PAO + arthrocentesis, glenoid labrum and femoral head trimming 6. Dysplasia + flat hip deformity, PAO+/- head reduction; 7. Complete dislocation of the hip joint, take modified Colonna arthroplasty+/- PFO+/- acetabular capsulorrhaphy. (D) Postoperative precautions: 1, start to do contraction exercises of quadriceps muscle on the first day after operation; 2, start to do hip flexion and extension and abduction exercises after suspending the affected limb on traction bed about three weeks after operation; 3, walk without weight bearing with crutches under the condition of no pain at the osteotomy place six weeks after operation and start to practice the function of gluteus medius muscle in side-lying position; 4, give up crutches and walk three months after operation. Evaluation of efficacy 1. Functional evaluation: according to the Harris score of the hip joint to evaluate the recovery of joint function; 2. X-ray evaluation: changes in the CE angle and AC angle before and after the operation.