Crowe type IV hip dislocation is the most serious type of congenital hip dysplasia, manifesting as complete dislocation of the femoral head, significant shortening of the lower limbs, severe dysplasia of the acetabulum and upper femoral segment, and even deformity, which may require total hip replacement in adulthood due to osteoarthritis of the prosthetic socket. However, the operation is difficult and has many complications. If the prosthetic socket is built in the true socket position, injury to the sciatic or femoral nerve may occur due to the lengthening of the limb. Therefore, how to reconstruct the hip joint while avoiding damage to the sciatic nerve or femoral nerve is a difficult problem for joint replacement surgery. From 1998 to February 2004, a total of 35 cases (39 hips) of Crowe IV congenital hip dislocation underwent total hip arthroplasty in our department, and all cases, except 1 deleted 2 hips, were reconstructed in the real socket area. Data and methods 1. Clinical data: From January 1998 to February 2004, a total of 35 cases (39 hips) of Crowe Iv congenital hip dislocation underwent total hip arthroplasty, all were female, aged 36-56 years old at the time of surgery, with an average age of 46 years. The patients with hip pain and difficulty in walking, for which conservative treatment was ineffective, were considered as indications for surgery. The average preoperative hip function score (Harris score) was 43. 2. Surgical method: The main point of surgery is to completely release the soft tissues around the hip joint and to cut off and release the adductor muscle if the hip joint is stiff and the hip is internally deformed. Routinely cut the iliopsoas tendon: along the resected joint capsule, find the true acetabulum. Remove the fibrofatty tissue filling the acetabulum. After understanding the bone quality of the anterior, posterior, superior and inferior edges of the true acetabulum. The acetabulum is first polished with a small file (usually 38 mm), and the acetabular file is gradually increased to compact the bone and expand the acetabulum by counter filing to a suitable size (usually less than 46 mm), after which the femoral side of the non-cemented acetabular prosthesis should be placed alternatively. The femoral neck osteotomy line should be close to the upper edge of the rotor in order to allow the stem to sink as far as possible and avoid excessive lower extremity lengthening. In cases of difficult repositioning, the periprosthetic soft tissues should be further released. If the hip is difficult to reposition, the periprosthetic soft tissues should be further released, including transverse cut of the iliotibial bundle, subperiosteal release and stripping of the starting point of the rectus femoris muscle. The patient’s periapical soft tissues were cut off transversely, including the iliac tibial bundle. A total of 3l cases and 35 hips were followed up, of which 27 cases were unilateral taxation and 4 cases and 8 hips were bilateral dislocations, and the interval between the two operations was 6-8 weeks. Non-cemented prosthesis was used on the acetabular side, and non-cemented prosthesis was used on the femoral side in 26 cases of 30 hips and cemented prosthesis in 5 cases of 5 hips. The size of the acetabular prosthesis was less than or equal to 46 n I. Most of the femoral stems were small-sized prostheses. Among the 31 cases and 35 hips, 2 hips were reconstructed at the same site of the prosthesis, while the rest were at the real site. In case 2, those who had undergone subrotor osteotomy in the past were first corrected by subrotor osteotomy. The results were obtained from 31 patients with 35 hips, 5 cases of 5 hips had intraoperative fractures, including 3 cases of 3 hips with minor rotor fractures and 2 cases of 2 hips with incomplete major rotor fractures. 2 cases of small rotor fractures were fixed with wire loops. The other 1 case was not specially treated, and the 2 cases of incomplete fractures of the greater trochanter were fixed with wire as “8”. Heterotopic ossification occurred in 3 hips, all of which were Brook 1/type and were treated specially. During the follow-up period, no postoperative infection occurred in any case. Intraoperative complications such as postoperative medullary joint dislocation, prosthesis detection and deep vein thrombosis with obvious clinical manifestations appeared in t cases of postoperative sciatic nerve irritation and the other case of femoral nerve irritation, both of which recovered within one month: the rest of the patients did not see obvious signs of nerve injury. Postoperative limb lengthening reached 4-6 c average 5 cn . The limb shortening was satisfactorily corrected. The majority of patients had no claudication or only mild claudication. The mean Ha s score at follow-up was 87. Discussion Indications for surgery: Crowe type IV congenital hip dislocation patients had very severe limb shortening and claudication. Due to the long-term lack of normal stress stimulation. The acetabulum (true socket) and the anatomical structure of the upper femur often have obvious developmental abnormalities. Due to long-term dislocation, thickening and contracture of the joint capsule and its surrounding soft tissues, as well as poor function of the abductor muscles, the above factors make total hip replacement surgery difficult. Intraoperative and postoperative complication rates are high: moreover, even after total hip replacement, some patients have shortened limbs and contractures. In some patients, limb shortening and claudication cannot be completely corrected. Therefore, limb shortening and claudication should not be considered as indications for surgery. Especially for some young patients, it is sometimes impractical to try to correct limb shortening and limp for aesthetic purposes by total hip arthroplasty, and it may even bring irreparable damage to the patient. Therefore, total hip arthroplasty should not be preferred for patients with Crowe IV congenital hip dislocation who only have claudication and limb shortening. Total hip arthroplasty should be considered only if the patient has pain and joint dysfunction due to osteoarthritis of the prosthetic socket, which seriously affects his or her daily life and work. Selection of surgical approach: Most authors advocate that the trans-rotor approach should be the first choice for total hip replacement in congenital hip dysplasia because it can reveal the true socket well and allow for simultaneous osteotomy of the upper femur. However, the trans-rotor approach requires a greater trochanteric osteotomy, and active abduction and passive adduction of the hip must be restricted for 6-8 weeks after fixation of the greater trochanteric osteotomy, which slows down the rehabilitation process after total hip arthroplasty to some extent. Moreover, for Crowe IV congenital hip dislocation, if the acetabulum is reconstructed at the true socket site, the gluteus medius muscle tone is high, making the repositioning and fixation after greater trochanteric osteotomy very difficult, thus increasing the difficulty and time of surgery and can lead to the occurrence of osseous discontinuity. Therefore, a lateral approach has also been recommended. The lateral approach can often damage the abductor muscle, which can further weaken the function of the abductor muscle and easily cause postoperative hip instability. In our group, the posterior lateral approach was used, and the incision was clearly exposed and did not damage the gluteus medius muscle, thus facilitating early postoperative functional exercise. Moreover, the incision can well reveal and monitor the tension of the sciatic nerve during surgery and repositioning to prevent intraoperative damage to the sciatic nerve. If a superior femoral osteotomy is required, it can be performed successfully by simply extending the incision distally. Therefore, we recommend a posterior-lateral approach for total hip arthroplasty in Crowe IV congenital hip dislocation. The location of acetabular prosthesis reconstruction: There is still a controversy about whether the acetabular prosthesis should be reconstructed at the level of the true socket or at the level of the false socket. Some people believe that the patient has been dislocated for a long time and has adapted to the non-physiological state of motion, so there is no need to emphasize reconstruction at the level of the true socket. However, prosthetic socket reconstruction, due to excessive upward shift of the hip rotation center, has the following insurmountable defects: (1) little limb lengthening, limited improvement of hip abductor function, and patients can still have significant limp after surgery; (2) abnormal force on the hip joint and increased wear of the prosthesis, which affects the service life of the artificial joint; (3) the bone in the prosthetic socket area is usually thin, which makes it difficult to ensure its initial stability even if a small-sized prosthesis is applied; and (4) The upper femoral segment may collide with the anterior superior iliac spine and the sciatic tuberosity during hip flexion and extension. Therefore, most studies have concluded that the acetabulum should be reconstructed at the level of the true socket in order to restore the normal anatomical and mechanical function of the hip joint . In our group, except for one case (2 hips) of Crowe type IV, the acetabulum was reconstructed at the prosthetic socket site, and all patients were reconstructed at the true socket site, and the postoperative limb shortening was satisfactorily corrected, basically reaching limb equinus or shortening of less than 1.5 om, and most patients had no claudication or only mild claudication. Therefore, how to ensure the initial stability of the socket prosthesis is a major difficulty in total hip arthroplasty. During surgery, care should be taken to protect the bone around the true socket, and a small or extra-small size prosthesis is usually required. The acetabular expansion file should be marked by the socket and teardrop, taking care to protect the anterolateral and medial walls of the acetabulum. The last No. 1 acetabular file should be filed backwards to expand the acetabulum by compacting the bone so as not to remove too much bone and affect the stability of the socket prosthesis. Prevention of nerve injury: Some scholars believe that excessive limb lengthening may be the main cause of nerve injury after total hip arthroplasty in patients with congenital hip dislocation . Therefore, it is advocated that in Crowe IV patients, limb lengthening should be controlled at 2-4 cm, and if limb lengthening is expected to exceed 2-4 cm, a shortened osteotomy of the upper femoral segment should be performed. However, some studies have found that nerve injury after total hip arthroplasty may be mainly related to previous surgical history, deformity of the upper femur, and severe flexion contracture of the hip, but not to the amount of limb lengthening. This is generally consistent with the results of this study. All the cases in this group had obvious limb shortening before surgery, and the postoperative limb lengthening reached 4-6 cm, with an average of 5 cm, and there was no nerve injury except for 2 cases with nerve irritation symptoms (1 femoral nerve and 1 sciatic nerve). The author’s experience is that when performing total hip arthroplasty in Crowe type IV patients, prolonged pulling of the hook to compress the sciatic nerve should be avoided intraoperatively. At the same time, the knee joint should be placed in a flexed position during dislocation and repositioning to ensure that the sciatic nerve is in a relaxed state. In those with a history of previous hip surgery, the sciatic nerve is often adherent to the surrounding scar tissue and should be carefully dissected during surgery to prevent direct injury to the sciatic nerve. The knee joint should still be placed in the flexed position before waking up from postoperative anesthesia, and gradually straighten the knee joint under close monitoring after waking up in order to prevent strain injury to the sciatic nerve. The necessity of shortening osteotomy: Some studies have concluded that total hip replacement for Crowe type IV congenital hip dislocation should be routinely performed by shortening osteotomy of the upper femoral segment. The reasons are: (1) even with extensive soft tissue release, there are still difficulties in repositioning; (2) excessive lengthening of the limb may damage the sciatic or femoral nerve; (3) some patients have difficulty in inserting a femoral stem prosthesis due to developmental abnormalities or deformities of the upper femoral segment caused by previous osteotomies of the upper femoral segment. However, performing a shortened osteotomy can result in (1) unsatisfactory correction of limb shortening and permanent postoperative claudication; (2) increased surgical difficulty and time; and (3) reduced initial stability of the prosthesis and delayed recovery time. As long as the preoperative preparation is adequate, the prosthesis is selected appropriately, and the soft tissues are sufficiently released, it can generally be successfully repositioned without damaging the sciatic or femoral nerves, and shortening osteotomy is not necessary routinely. In this group of cases, except for 2 cases with previous subrotor osteotomy and deformity of the upper femur, re-osteotomy was performed to facilitate the insertion of the prosthetic stem and implantation of a non-mud-type prosthesis, but no shortened osteotomy was performed in the rest of the cases.