Developmental dysplasia of the hip (DDH) is a congenital disorder that causes increased stress in the hip joint due to developmental disorders, ultimately leading to osteoarthritis of the hip joint. Patients with DDH without pain do not require surgical treatment, but imaging and clinical follow-up are required every 1-2 years for observation; steroids and high-energy hip activities should be avoided. Once hip pain is present, especially in patients with limited daily activities, surgical treatment is required. Methods include arthroplasty, pelvic osteotomy, femoral osteotomy and joint fusion. The main purpose of surgical treatment is to reduce pain, improve hip function, and stop or delay the development of osteoarthritis. 1. Osteotomy Osteotomy is suitable for young, symptomatic patients with DDH without excessive deviation of the center of rotation of the hip towards the proximal end, good joint mobility, and no or mild joint degeneration (T?nnis grade 0~I) [1,2]. The initial symptoms of most DDH patients mainly originate from the acetabular side deformity of the hip joint, and pelvic osteotomy can more ideally correct the anatomical deformity on the acetabular side. In contrast, proximal femoral osteotomy corrects the secondary deformity on the femoral side and can be considered as an independent orthopaedic procedure as well as an adjunct to pelvic osteotomy. 1.1, pelvic osteotomy Pelvic osteotomy is divided into two categories according to the degree of acetabular dysplasia deformity and arthritis, namely reconstructive osteotomy (RO) and salvage osteotomy (SO). 1.1.1, RO RO is indicated in the early stage of osteoarthritis and aims to reconstruct the near normal anatomical structure and biomechanics of the hip joint, restore the near normal cephalo-malleolar relationship, improve the coverage of hyaline cartilage, improve symptoms and prevent degeneration. 1.1.1.1, I, II and III phase osteotomy: Salter first reported the Salter I phase osteotomy in 1961 for children with DDH under 6 years of age, the advantage of which is that the osteotomy at the ilium can rely on changing the acetabular orientation to reconstruct the hip joint, allowing it to immediately achieve stable weight bearing without changing the flatness of the acetabulum or impairing its function. sutherland in the last century In 1965, Le Coeur first reported a triphasic osteotomy of the pelvis, in which the pubic bone and the sciatic bone were amputated near the femoral joint to improve the coverage of the acetabulum over the femoral head, but the size of the bone, the attached muscles and the ligaments of the sacral junction limited the result to a satisfactory correction, resulting in a significant pelvic asymmetry. The triphasic osteotomy reported by Steel in 1973 differed in that the sciatic osteotomy was performed away from the joint and by three incisions; the pars interarticular triphasic osteotomy performed by Carlioz and Tönnis, which avoided the sacro-pelvic ligaments that limit the movement of the osteotomy block, significantly improved the correction rate [3]. One-phase, two-phase, and three-phase osteotomies are indicated in early childhood and children. Adolescents and adults, on the other hand, are not suitable for this type of surgery because of their poor pelvic compliance, ligamentous soft tissue restriction of acetabular rotation that can easily cause destruction of the pelvic ring, significant postoperative pelvic deformation, and difficulty in accepting external fixation in plaster. At present, the popular reconstructive osteotomies for the treatment of DDH in adolescents and adults are rotational acetabular osteotomy (RAO) [4] and periacetabular osteotomy (PAO) [5]. 1.1.1.2, PAO: PAO is also known as Bernese osteotomy. It requires only one incision and can fully correct the deformity in all directions, including external and anterior rotation of the osteotomy block and correction of the center point of the hip joint; the posterior pelvic column is intact and the blood supply to the acetabular osteotomy block is good; after correction, the bone block is fixed with screws without plaster and other external fixation, and the patient can get out of bed early; the true pelvic structure is not destroyed, so that female patients can deliver naturally after surgery; the abductor muscle can be protected from injury, but the postoperative mobility is slight. However, the mobility of the hip joint is slightly affected after surgery. This procedure is suitable for DDH patients between 15 and 50 years old (Y cartilage is closed), with hip pain but basically normal mobility, no deformation of the femoral head on X-ray, good correspondence between the head and socket of the external booth Xray, osteoarthritis below T?nnis grade I, and basically normal joint space. In contrast, this procedure is not recommended for patients who are too young with unclosed acetabular epiphysis, too old with severe osteoporosis, >50% restriction of hip mobility, significant femoral head deformation, osteoarthritis above T?nnis grade II, and joint space narrowing with poor prognosis [4,5]. Ganz et al [5,6] reported in 1999 the clinical outcome of 63 patients (75 hips) with or without secondary hip degeneration with a mean follow-up of 11.3 years (10-13.8 years), achieving an excellent rate of 73%.Trousdale et al [7] reported 42 patients with osteoarthritis of the hip, most of whom were female patients with a mean age at surgery of 37 years , the degree of arthritis was classified according to T?nnis criteria (grade I in 15 cases, grade II in 18 cases, and grade III in 9 cases), and the mean follow-up of the surgery was 4 years. The Harris score ranged from 62 (33-95) preoperatively to 86 (29-100) postoperatively. The results showed excellent outcomes in 32 hips with mild and moderate osteoarthritis; however, eight of the nine patients with grade III osteoarthritis had further progression of arthritis in the hip and had Harris scores below 70, six of whom subsequently underwent total hip replacement. RAO had good outcomes in patients with osteoarthritis on a T?nnis scale of 0 to I who had symptoms of hip pain, but in However, satisfaction with the procedure is low in patients with more severe osteoarthritis. In addition, because of the difficulty of this operation, if the osteotomy surface enters the joint during the operation, it may cause reduced hip mobility and joint pain; if the acetabulum is excessively displaced, it may cause reduced hip abduction muscle strength; if the osteotomy end gap is large, the osteotomy is prone to delayed healing or non-healing; and ectopic ossification may reduce hip mobility; some patients have symptoms of lateral femoral cutaneous nerve injury [8]. 1.1.1.3, RAO: The principle of acetabular rotational osteotomy is to make an arc-shaped osteotomy of the bony part of the acetabulum while keeping the joint capsule intact, and to rotate the osteotomized acetabulum forward, outward, and downward to increase the coverage of the acetabulum on the femoral head and enhance the stability of the hip joint. The acetabular dysplasia is anatomically corrected and the factors of weight-bearing cartilage degeneration of the hip joint are eliminated. The procedure reconstructs the normal anatomical relationship of the hip joint, and also increases cellular activity, improves blood flow around the hip joint, promotes the development of acetabular cartilage, and creates conditions for the continued development of the hip joint; the acetabulum moves outward, downward, and forward to fully cover the femoral head, so that the pressure acting on the acetabulum by the femoral head is dispersed and the pressure is reduced; as the acetabulum rotates inward, the femoral head also moves inward, according to According to the pauwels theory, the combined force on the femoral head is reduced due to the extension of the force arm between the center of the femoral head and the greater trochanter [9]. The indications are as follows. (1) the “Y” cartilage of the acetabulum has closed; (2) the CE angle is less than 20°; (3) early osteoarthritis of the hip joint.Ito H et al [10] followed up 101 patients (110 hips) for a mean of 8.3a with a satisfactory outcome of 85%; 8 cases (7%) had Trendelenburg’s sign, CE angle was corrected to a mean of 35°, and hip degeneration to osteoarthritis was seen on imaging in 14 hips (13%). Complications included deep infection (1 case), pulmonary embolism (1 case), and osteonecrosis of the rotated osteotomy block (2 cases). The Ollier lateral U-shaped transcondylar approach provided better exposure for the osteotomy and relieved hip pain in most patients. 1.1.2, SO SO is indicated in advanced stages of osteoarthritis to improve bony coverage of the acetabulum and is used to relieve painful symptoms when structural coverage of the hip cannot be reconstructed. It is represented by the Chiari osteotomy created by Chiari in 1955, which increases the weight-bearing surface of the femoral head anteriorly, posteriorly and laterally in the acetabulum, eliminates the tendency of joint subluxation, moves the neck of the femoral head inward, and increases abductor muscle tone. Chiari’s internal pelvic displacement osteotomy, a representative of salvage osteotomy, was first reported by Chiari, an Austrian orthopedic surgeon, in 1955 [11], and is essentially an acetabular cap procedure, which aims to enlarge the acetabulum to increase the inclusion of the femoral head. The advantages of the Chiari osteotomy compared to other internal displacement osteotomies are that the iliac bone is less susceptible to bone resorption because of its blood flow, and that it has good stability. The disadvantage is that there is no hyaline cartilage surface on the outer edge. Although fibrocartilage can be produced on the surface of the bone by the impingement of the femoral head later on, this cartilage is thinner and less smooth and wear-resistant than hyaline cartilage. The indications are as follows. (1) the range of motion of the joint is at least 70° of flexion and extension, with abduction and adduction; (2) the shape of the femoral head is basically normal; (3) the head of the femur fits into the acetabulum when the hip is fully internally rotated and abducted at 30°; Chiari himself followed up 49 patients who underwent Chiari internal displacement osteotomy between 1960 and 1967 for 10-17a, and found that 37 cases had excellent results, accounting for 87%. Subsequently, Chiari followed up 100 patients with severe preoperative osteoarthritis for 2-10a, with a failure rate of 15% [12]. 1.2. Femoral osteotomy Femoral osteotomy is indicated when the proximal femoral deformity is the main body or when pelvic osteotomy cannot adequately complete the orthosis. Some data [1] show that 27% of periacetabular osteotomies require a proximal femoral osteotomy to aid in the orthopedic process. However, in some patients, a proximal femoral osteotomy can be performed alone. Most patients with mild acetabular deformity with hip exostosis are suitable for a stand-alone internal femoral trochanteric osteotomy to improve joint fit. The distal segment of the femoral osteotomy can also be used as an adjunct to cover the anterior femoral head and correct the hip flexion deformity. A small number of patients with hip dysplasia have a flattened femoral head with a large amount of medial osteochondral tuberosity. For this type of deformity, an external osteotomy at the femoral trochanter can improve the coverage of the joint and move the center point of the femoral head inward to improve the function of the abductor muscle. 2.Artificial joint replacement 2.1.Artificial total hip replacement (THA) Artificial hip replacement has become the best choice for treating patients with advanced DDH complicated by severe osteoarthritis, and the abnormal anatomical structure of the hip joint in DDH patients increases the difficulty of the operation. Regardless of the method of acetabular repair, the coverage of the artificial cup should be more than 75% and the outer upper part of the acetabulum should be bony covered; otherwise the stresses acting on the acetabulum will be transferred to the posterior upper part of the acetabulum and the interface between the bone cement and the artificial cup, thus increasing the rate of acetabular loosening [13,14]. The application of an artificial total hip prosthesis requires reference to the Crowe staging of patients with DDH [15]. For patients with DDH with Crowe type I, a non-cemented prosthesis can be placed in or around the true acetabulum with mild internal displacement; for patients with type II, III, and IV, a non-cemented prosthesis can be placed in or around the true acetabulum, and if necessary, an autologous bone graft can be placed around the acetabulum; for the femoral end, a cemented or biologic prosthesis should be selected with reference to the patient’s age, bone quality, and morphology; for patients with type IV, the femoral side In type IV patients, cemented or biologic prostheses should be implanted after appropriate osteotomy at or below the trochanter. Since the level of the true socket is the most rich in bone reserves, the ideal site for placement of the artificial cup is at the level of the true socket. Various methods can be used for acetabular reconstruction, such as application of small cups, built-in cups, pelvic osteotomies, and autologous and allogeneic bone grafts. Harris [13] was the first to propose the application of the intraoperatively resected femoral neck as a source of bone graft for autologous bone grafting and was adopted by most people with acceptance. It is generally accepted that the use of autologous bone graft to repair acetabular defects is superior to allogeneic bone graft, and the area of the acetabular cup should be less than 30%-40% of the acetabular cup area when bone graft is applied to cover the acetabular cup. However, the results of Morsi et al [16] showed that there was no significant difference in the effect of bone grafting with or without the application of bone cement to fix the acetabular cup after using either autologous or allogeneic bone graft to repair the acetabular defect, and it is recommended that a non-bone cement press-fit method be applied to fix the acetabular cup after using autologous or allogeneic bone graft to repair the acetabular defect. If allogeneic bone graft is applied to cover 40% or more of the acetabular cup, bone cement is used to fix the acetabulum. iida et al[17] showed a 75% survival rate of acetabular prosthesis in a mean 12.3-year follow-up of patients with DDH treated with prosthetic total hip arthroplasty using bone cement. Proximal femoral deformities due to dysplasia need to be addressed during femoral reconstruction. Because the femoral marrow cavity is often narrower and straighter, a prosthesis with a smaller, shorter and straighter stem is often required. For Crowe type I-III DDH, a smaller conventional femoral prosthesis can meet the needs; however, for type IV, there is often no femoral spur at the osteotomy, so a specially designed femoral prosthesis with a straighter, narrower and limited internal curved stem is often required. If the anteversion of the femoral neck is greater than 40°, a simultaneous rotational osteotomy of the femur is often required. In the treatment of high DDH, if the femoral head is placed in the true socket position, simultaneous shortening of the femur is often required to avoid damage to the sciatic nerve. In general, the limb should not be lengthened more than 4 cm, otherwise the risk of sciatic nerve injury can be significantly increased. Lewallen [18] suggested that it should be limited to 4 cm or 6% of the ipsilateral limb. In general, the incidence of nerve injury in THA is 0.2%-2%, while it can be as high as 3%-15% in the treatment of DDH, for reasons mainly related to the limb lengthening involved in the procedure [13]. Postoperative complications also include infection, joint dislocation, and prosthesis loosening. With the development of the so-called “modern bone cement technology” and the common application of hybrid total hip replacement, the loosening rate of the femoral prosthesis has decreased significantly. In the mid-1990s, metal-to-metal hip replacement was used to replace the femoral head and acetabular neck with a metal “shell”. In the mid-1990s, metal-to-metal surface replacement of the hip joint, as well as cemented and uncemented acetabular prostheses, were used to achieve satisfactory early and mid-term outcomes [19]. Its superiority is demonstrated by the fact that firstly, surface replacement can relieve the patient’s pain while restoring the joint mobility to a level close to normal. The reason for this is that the original structure is retained to the maximum extent, which can meet the need for greater mobility; secondly, the joint prosthesis is designed with a large head, which ensures the stability of the hip joint during activity and is ideal for young patients with high hip mobility requirements; furthermore, because the surface replacement involves only the articular cartilage and preserves the original femoral neck and femoral head, the difficulty and efficacy of revision are basically equivalent to that of the initial total hip replacement. Contraindications to surgery include, in addition to those required for conventional total hips, such as systemic or local infection and important organ insufficiency, (1) a neck stem angle of less than 110°. Silva et al [20] analyzed the biomechanical properties of the hip joint and concluded that placement of the femoral head prosthesis in the position of mild valgus is a guarantee of the durability of the prosthesis after surgery, while for patients with internal hip rotation, the shear force is For patients with internal rotation of the hip, it is not suitable for hip surface replacement because the shearing force is too large and it is easy to induce femoral neck fracture. (2) The chance of femoral head fracture and ischemic necrosis after surgery is significantly increased in patients with cystic lesions on the femoral head with a diameter of more than 1 cm or a range of more than 25% of the femoral head. (3) Those whose acetabular position is too high and the difference in bilateral limb length is too great. The surface replacement prosthesis itself has no role in lengthening the limb, and it is almost impossible to reconstruct the acetabulum in true socket position without osteotomy orthopedics of the femur in those with high dislocation. (4) Patients with fractures or bony structural defects of the femoral head and neck. (5) Patients with renal insufficiency. Since the concentration of metal ions such as metal cobalt, chromium and nickel in blood and urine will increase accordingly after metal-to-metal prosthesis implantation, although there are no reports of kidney function damage induced due to the increase in metal ion concentration, the surgery for such patients should be done with caution. The main complications of metal-to-metal total hip surface replacement include femoral neck fracture, loosening, infection, ischemic necrosis of the femoral head, dislocation, neurovascular injury, and elevated metal ion levels, etc. The Oswestry Outcome Centre reported [21] that all reasons for revision were, in order, femoral neck fracture 56%, loosening 19%, infection 11%, ischemic necrosis of the femoral head 11%, dislocation 3 necrosis 11%, and dislocation 3%. It is evident that femoral neck fracture is the main complication causing prosthesis failure. Mont [21] reported that 22% of the 50 patients in whom he performed this procedure early on had a femoral neck fracture within 5 years, but only 1 fracture occurred in 250 patients later on, suggesting that intraoperative technique is an important factor influencing postoperative complications. Intraoperative damage to the femoral neck cortex, excessive removal of the periprosthetic bone, positioning of the centrally positioned rod outside of the central axis of the femoral neck, and a small cervical stem angle are all risk factors for later femoral neck fracture. After metal-to-metal prosthesis implantation, the concentration of cobalt and chromium metal ions in the patient’s serum, red blood cells, and urine gradually increases over time and reaches a plateau about 2 years after surgery [22], but the concentration of metal ions is not related to the magnitude of joint mobility, that is, the range of elevated metal ion concentration is not related to the intensity of wear [23].Hallab [24] analyzed cell mediated allergic reactions in patients receiving different combinations of prostheses found that the proliferation of lymphocytes was significantly higher in the metal-to-metal group than in the metal-to-polyethylene and unoperated groups, and that the rate of positive lymphocyte reactions was positively correlated with the level of metal ion concentration in the serum. What clinical significance these data have is not known, but the possibility of prosthesis failure due to metal allergy cannot be ruled out yet. In addition, phenomena such as chromosomal aberrations detected in patients who have undergone metal-to-metal prosthesis replacement [23], although the relationship with increased metal ion concentrations cannot be proven at this time, the significance of this series of biological phenomena accompanying the changes produced by metal-to-metal prosthesis implantation, as well as the effect on specific physiological conditions such as pregnancy and impaired renal function, needs to be further investigated. 3.Arthrofusion Hip fusion is only applicable to patients with unilateral DDH who are not eligible for osteotomy orthopedic surgery or arthroplasty. Joint fusion improves pain symptoms while limiting joint movement and accelerates bone degeneration in the ipsilateral knee and lumbosacral region. In conclusion, the treatments for patients with DDH vary by age and degree, and they provide different perspectives and degrees of pain relief and improved joint function, allowing DDH patients to regain a pain-free, more mobile hip. Although there are some shortcomings in these treatments, we believe that in the near future, with the continuous development of material science and surgical techniques, these treatments will be further improved for the benefit of the people.