High-energy injuries often cause acetabular fractures, and even when internal fixation surgery can reconstruct a satisfactory acetabular joint surface, the incidence of postoperative traumatic arthritis of the hip is still as high as 57%, in addition to ischemic necrosis of the femoral head, which occurs in 2 to 40% of cases. Therefore, once these conditions occur, patients may need to undergo total hip arthroplasty (THA). The indications for THA after acetabular fracture are rarely: 1) the patient has a more serious arthrosis in the hip joint before the fracture and needs artificial joint replacement; 2) the acetabular fracture is combined with femoral neck fracture or femoral head splitting fracture; 3) the patient has severe osteoporosis and the internal fixation cannot provide firm fixation. The indications for THA in the late stage of acetabular fracture are: 1, occurrence of traumatic osteoarthritis; 2, necrotic collapse of the femoral head; 3, severe heterotopic ossification. The three major complications mentioned above will cause hip pain and impaired joint motion, and the patient will eventually undergo THA. 7. 8 years from the time of acetabular fracture to THA was reported by Romness et al. and about 9 years by Weber et al. Preoperative preparation Preoperative erythrocyte sedimentation rate and C-reactive protein should be routinely measured. The use of a posterior expanded approach for acetabular fractures, obesity, long-term use of nonsteroidal drugs or hormones, diabetes mellitus, immunodeficiency, and radiation therapy are all high-risk factors for the development of infection. Preoperative leukocyte classification, sedimentation, C-reactive protein measurement and culture of the puncture fluid as well as intraoperative biopsy can be helpful in diagnosing infection. If the diagnosis of infection is clear, intraoperative joint irrigation, antibiotic infusion and antibiotic bone cement between the prosthesis and the interface should be performed, and the femoral neck and necrotic bone mass should be removed and a negative pressure drain placed. Depending on the circumstances, a stage I or II joint replacement is performed. In addition to the conventional orthopantomogram of the pelvis and the frontal and lateral radiographs of the affected hip, in the author’s hospital, CT thin-section scans are also routinely performed, which have clarified the acetabular bone structure, including the bone defect situation and the location of ectopic bone, etc. In addition, CT thin-section scans help to determine the position of the internal fixation, especially the screw position, and help to predict whether the screw will interfere with the acetabular prosthesis installation. The surgical approach, internal fixation management and acetabular defect or heterotopic bone management are selected accordingly. Surgical technique The surgical approach depends on the following points: (1) the surgical approach to the original acetabular fracture; (2) whether the internal fixation and ectopic bone need to be removed; (3) whether there is a combined sciatic nerve injury; and (4) the familiarity of the surgeon with the approach. In my hospital, the posterior-lateral approach is mostly used for this type of patients, and good results have been achieved, with no complications such as loosening and sciatic nerve injury so far. If a posterior approach (e.g., Kocher-Lagenbeck approach) was previously used, attention should be paid to previous scar adhesions when choosing a postero-lateral approach to THA. The external rotator muscle group is severed along the interrotor line, and if there is no preoperative manifestation of sciatic nerve injury, the sciatic nerve is usually not revealed, but its integrity should be palpated and protected. The postero-lateral approach allows for greater exposure of the posterior aspect of the acetabulum and meets almost all the requirements for THA except for the occasional need to combine an anterior approach to aid in the removal of the anterior acetabular screws. If an anterior approach has been used for previous fracture fixation, care should be taken when using the postero-lateral approach to release the anterior acetabular rim, as the adherent scar tissue may cause anterior vascular damage, but incomplete release may result in difficult repositioning after prosthesis placement, which is particularly common in patients with femoral head dislocation. The acetabular prosthesis is primarily a biologic prosthesis, with bone cement prosthesis being used sparingly. In most cases, a normal biologic acetabular prosthesis is sufficient. We will consider using high friction acetabular prosthesis, such as Zimmer’s metal trabecular prosthesis, in the following cases: 1) acetabular bone defect; 2) sclerosis or necrosis of displaced fracture mass; 3) after proper reaming of the acetabulum, some scar tissue remains in the acetabulum, which may affect the normal bone ingrowth. The current classification methods for acetabular bone defects are mainly AAOS classification, Paprosky classification and Gross classification. We believe that Gross classification is more applicable to the description of bone defects after acetabular fracture, and Gross classification classifies acetabular bone defects into type I inclusive bone defects and type II non-inclusive bone defects. Inclusive bone defects have an intact acetabular ring and can be operated with either a plain or a revision prosthesis (acetabular rim fixation) with the defect area filled with granulated bone. Non-inclusive bone defects are further divided into two subtypes, IIA and IIB. Type IIA is a defect of the acetabular roof or part of the acetabular column, but the missing area of the acetabular wall does not exceed 50% of the entire acetabular area. type IIB is a defect of one or both columns, and the missing area of the acetabular wall exceeds 50% of the acetabular area. The reason for the 50% cut-off is that the initial stability of the acetabular prosthesis relies on the clamping effect of the acetabular ring, and when the residual acetabular ring exceeds 50%, it is able to provide effective clamping of the acetabular prosthesis without the need for auxiliary support. Conversely, when the acetabular ring is unable to provide effective clamping of the acetabular prosthesis, adjunctive support, such as the use of large structural bone grafts or metal reinforcement blocks, or even reinforcement rings, has to be implemented. The need to remove the internal fixation at the time of joint replacement is controversial. In our opinion, if the internal fixation (whether plate or screw) does not prevent proper placement of the acetabular prosthesis, it can be left in place. This not only reduces the difficulty of surgery, intraoperative bleeding and trauma, but also helps to establish the initial stability of the acetabular prosthesis. In addition, screws that penetrate the internal wall should be removed with greater caution, as they can cause uncontrollable bleeding on one side. In patients with acetabular fractures, especially those treated surgically, the incidence of heterotopic ossification ranges from 14% to 33% for grades I-II and 4% to 26% for grades III-IV, according to the Brooker classification. Modified iliofemoral approach, associated femoral fracture, sciatic nerve injury, and “T” fracture are the factors that predispose to heterotopic ossification. We usually follow the following principles for removal of heterotopic bone: obstruction of visual field during surgery; obstruction of joint dislocation or repositioning; heterotopic bone affecting the range of motion of the joint after repositioning, or joint instability due to collision. If these conditions occur, we will remove the ectopic bone, otherwise we will try not to remove it to avoid unnecessary injury or bleeding. When dealing with bone discontinuity, for acetabular morphology can meet the coverage of acetabular cup, it can not be repositioned, remove acetabular cartilage, occlude the sclerotic bone or fibrous tissue at the broken end, install acetabular prosthesis after bone grafting, and choose porous revision prosthesis to effectively fix the fracture end of bone discontinuity with the help of screws, without external plate fixation of acetabulum. However, for some cases of bone discontinuity, firm fixation with reconstructed plates is required to obtain satisfactory coverage of the acetabular cup. Postoperative considerations Postoperative anticoagulants are used for 5 weeks; patients begin non-weight-bearing functional exercises on the first postoperative day; the duration of weight-bearing on the affected limb should be determined by the type of prosthesis, type of bone graft, size, and stability. In patients with significant bone loss, full weight-bearing is usually delayed until 12 weeks postoperatively. Common complications Heterotopic ossification Heterotopic ossification is a common complication after total hip arthroplasty for acetabular fractures. The incidence reported in the literature is very inconsistent, ranging from 12% to 63% for cemented total hip replacements without prophylaxis, 26% to 80% for non-cemented prostheses, and 67.2% for HA-coated prostheses, while the incidence reported in China is lower, ranging from 6% to 33%. The lesions begin 3-6 weeks after surgery, and appear as cloudy shadows in the soft tissues around the hip. 2 months later, they enter the mature stage, and trabecular structures are visible, which can last for 1-2 years, and the incidence is about 3 times higher in men than in women, and the lesions are often distributed along the gluteus medius muscle. brooker divided the ectopic ossification into five grades: grade 0 without ectopic ossification shadow; grade I with bone island formation in the soft tissues; grade II with ossification blocks in the pelvis and proximal femur Grade III: there were ossified blocks in the pelvis and proximal femur, and the distance between them was less than 25 px; Grade IV: there was obvious bone bridge formation and hip joint straightening. The exact reason for the high incidence of heterotopic ossification in THA after fracture is not clear, and may be related to the long operation time, heavy soft tissue trauma, residual bone debris in soft tissue, and postoperative hematoma due to incomplete hemostasis. In most patients, heterotopic ossification is not clinically significant, and only 5-10% of patients are grade III or IV. If it affects joint movement or has significant pain, surgical resection is feasible. Surgery is generally considered to be performed after more than 1 year and after the heterotopic ossification foci have matured. However, the effect of surgical resection on pain and improvement of joint function is uncertain. For high-risk patients, anti-inflammatory pain and diphosphonate can be used for prevention. 25 mg of anti-inflammatory pain is given orally three times a day for 2-6 weeks. In addition low doses of radiation therapy, totaling 1000-2000 rad, given over 5-10 days immediately after surgery can also help prevent heterotopic ossification. Infection The incidence of infection has been reported to be significantly higher in acetabular fractures undergoing THA after internal fixation than in plain THA. Bucholtz et al. reported infection rates as high as 20%. Tile et al. suggested that this was related to the presence of low-grade osteomyelitis after internal fixation and recommended that hip puncture cultures be performed in all patients requiring THA after internal fixation of acetabular fractures to rule out potential low-grade infections. The aim of treating hip replacement infection is to eradicate the infection, eliminate pain, and restore function. The basic treatment principle is thorough debridement combined with antibiotic therapy. Thorough debridement is the basic prerequisite for all interventional procedures. It is best to use the original incision for debridement and, if possible, to remove the sinus tract as well. Intraoperatively, hematoma, scar tissue, necrotic bone and soft tissue, as well as prosthesis and residual internal fixation are thoroughly removed. Retaining the prosthesis and replacing the liner only may be considered if the following conditions exist: 1) the infection occurred within 3 weeks; 2) the prosthesis is stable; 3) the soft tissue is in good condition without large amounts of scar tissue; and 4) the causative organism is clear and sensitive to antibiotics. If the above conditions are met, the success rate of the surgery can still reach 82% to 100% even if the prosthesis is retained, and conversely, the success rate is only 14% to 68%. In addition, if the patient has also received a prosthesis in another joint or has received a heart valve replacement, it is not recommended to retain the prosthesis in order to avoid the spread of infection involvement. When the original joint prosthesis is not retained, a new prosthesis can be implanted immediately after complete debridement, i.e., phase I revision, or a new prosthesis can be implanted at a certain time interval after removal of the prosthesis, i.e., phase II revision. The main factors to be considered in choosing Phase I or Phase II are: 1) whether the bacteria are sensitive to antibiotics; 2) what is the condition of the bone and soft tissue, and whether there are obvious tissue defects; 3) whether the patient has “high-risk” infection factors such as diabetes; 4) whether the patient can tolerate multiple surgeries. However, the infection clearance rate is low and the reinfection rate is high, so it is not as common as stage II revision treatment.