I. Classification 1. Early infection: infection that occurs within 3 months after surgery; 2. Late infection: infection that occurs 3 months to 2 years after surgery; 3. Late infection: infection that occurs 2 years after surgery. Early infections have typical manifestations of acute joint infections, such as pain, effusion, erythema, and fever at the joint site. Generalized fever is seen in highly virulent bacterial infections, such as Staphylococcus aureus (S. aureus) and gram-negative bacilli (gram-negative bacilli), and cellulitis and sinusoidal tracts with pus elimination may occur in the course of the infection. Patients with late-onset infections (low-grade infections) present with mild symptomatic signs, such as loosening of the prosthesis and persistent joint pain, and the causative organisms are usually low-toxicity bacteria, such as coagulase-negative staphylococci and P. acnes. Late-onset infections are predominantly hematogenous in nature or implantation, and the causative organisms are often from skin, respiratory, dental, and urinary tract infections. II.Diagnosis The diagnosis of infectious loosening is first based on history, radiography, ESR, and CRP. Pain is evident at rest and with activity, but it is still difficult to differentiate aseptic loosening from infection after arthroplasty.Typical radiographic findings include irregular and toothed edges of the cortical bone, marked periosteal reaction, and advanced joint dislocation.2/3 of late infections and less than 50% of early infections present with loosening of the joint on radiographs. Arthrography is helpful in the diagnosis of cemented acetabular loosening, where the contrast agent enters between the cement and the bone, but the fibrous membrane between the cement and the bone blocks the contrast agent from entering its interstices, so it is prone to false-negative results. Blood routine is often normal, but elevated ESR and CRP are very important for the diagnosis of infection. Third, treatment 1, clear and retain the prosthesis: only for a small number of patients, to be used with caution. However, if the case selection is appropriate, the success rate can reach about 70%. The criteria for case selection include acute infection (symptoms appearing in less than 1 month), replacement of polyethylene liner, and antibiotic application for at least 6 weeks after debridement. 2. One-stage debridement and implantation of the joint (one-stage revision): the success rate is lower and there are certain indications. Remove all foreign bodies and apply antibiotic bone cement, but the cemented prosthesis is prone to early loosening. Phase II revision: Higher success rate, currently considered as the “gold standard” for the treatment of infection after arthroplasty. Thorough debridement includes removal of prosthesis and cement, placement of antibiotic-cemented spacer, and second-stage revision arthroplasty. Its main advantage is that it can be placed in compression-matched joints, and postoperative antibiotics should be used for more than 4 weeks, otherwise, there is a high recurrence rate (especially when the causative organisms are more virulent), and the prognosis of gram-negative and enterococcal infections is very poor, and the second-stage reconstruction should be carried out 12 months after first-stage debridement surgery. For low virulence infections phase II revision arthroplasty can be performed earlier (3 months). Antibiotic spacers provide a high local concentration of antibiotics and maintain lower limb length. antibiotic spacers need to be implanted in the medullary cavity and acetabulum, and can be used with light weightbearing after surgery. koo et al. reported that 21 out of 22 cases were successful, with 2 g of vancomycin, gentamicin, and cefotaxime mixed in with every 40 g of bone cement. 4. arthrotomy and plasty 5. joint fusion 6. amputation.