The goal of prosthetic joint replacement is to enable the patient to regain a pain-free, stable and functional new joint. Therefore, persistent postoperative pain is an unacceptable and important complication for both the patient and the operator and must be a serious concern and managed appropriately and promptly. The causes of persistent pain after artificial knee arthroplasty are numerous and need to be fully evaluated by detailed history analysis, physical examination, laboratory tests, and imaging analysis. The history taking process should focus on analyzing the characteristics of the pain, including the localization of the pain, is it localized or radiating? The time when the pain is most likely to occur, its duration, the factors that lead to the aggravation or relief of the pain, and the intensity of the pain. Physical examination begins with checking for increased skin temperature or redness; force lines and mobility of the knee joint; joint effusion or friction sounds and stability of the ligaments. Examination of pressure points around the knee joint can help us identify tendonitis, bursitis and subcutaneous neuroma (positive Tinel’s sign). A limping gait and lateral instability of the knee often suggest a poor force line or ligament instability. Excessive internal or external rotation of the foot suggests poor rotation of the tibial prosthesis, but, of course, the degree of poor rotation of the femoral or tibial prosthesis is best determined by CT examination. The physical examination also determines whether there is a lumbar spine or hip lesion that may be causing radiating knee pain. In addition, a detailed examination of the nerves and blood vessels should be performed. Psychological assessment is also important, and Ayers found that a score of <50 on the psychological portion of the SF-36 assessment form was often associated with increased pain and decreased function after TKA [1]. I. Diagnosis of postoperative joint infection or prosthetic loosening Infection is the most significant cause of persistent pain after artificial knee arthroplasty. Factors contributing to the increased risk of infection include advanced age, malnutrition [2], obesity [3], hormone use [4], skin ulcers, prolonged preoperative hospital stay, and the presence of medical comorbidities (e.g., rheumatoid arthritis [5], diabetes [6], psoriatic arthritis [7], and a history of previous knee infections [8]). Laboratory tests can help us to determine whether the cause of pain after TKA is due to infectious or non-infectious factors. Commonly used laboratory tests include ESR, CRP, blood phase analysis as well as classification, arthrocentesis line cell count and culture.ESR tends to remain elevated for 3-6 months after TKA [9].Barrack study found that ESR greater than 30 mm/h has a sensitivity of 80% and specificity of 62.5% for diagnosing infection [10]. However, Levitsky et al. found that an ESR greater than 30 mm/h had a sensitivity of 60% and a specificity of 65% for the confirmation of infection [11].CRP generally returns to normal levels 3 weeks after TKA. The combined application of ESR, CRP and blood phase analysis and classification can increase the sensitivity and specificity of infection detection. However, in patients with systemic diseases such as rheumatoid arthritis, ESR and CRP themselves change as the disease progresses, so an increase in ESR or CRP is not sufficient to suggest the presence of infection. To improve the accuracy of knee puncture detection of infection, smear or culture testing should be performed as early as possible after the puncture. If infection is highly suspected, multiple arthrocentesis may be performed if the initial culture is negative. In addition, patients should discontinue antibiotics for at least 2 weeks prior to puncture to avoid false-negative results. A joint fluid examination with a leukocyte count >2500/mm3 and a polymorphonuclear leukocyte percentage >60% often confirms the diagnosis of infection (sensitivity and specificity of 98% and 95%, respectively). On imaging, patients with pain after TKA may opt for routine or sub-stress X-rays of both knees, arthrography, or nuclear scans to help analyze the cause of the pain. Routine weight-bearing frontal and lateral x-rays of the knee should be performed to assess the fixation, position, and size of the prosthesis and the presence of prosthetic failure or periprosthetic osteolysis. An axial patellar radiograph can help assess patellar position and trajectory. A full-length lower extremity x-ray is useful to rule out the presence of bone nonunion, tumors, and stress fractures in the distal knee, which are easily overlooked on routine knee x-rays. Other examinations include orthopantomographs of the pelvis to check for stress fractures or osteoarthritis of the hip, the latter of which can be reflected along the saphenous nerve branch of the foramen occulta to the periprosthetic area of the knee. Retrospective analysis of preoperative knee X-rays is useful to determine the exact cause of pain; X-rays performed at each postoperative follow-up time point facilitate detection of progressive development of translucency at the prosthetic fixation interface, prosthetic displacement, and osteolysis and other imaging manifestations. Stress down x-rays are useful to detect ligament instability. Inversion or valgus sub-stress x-ray facilitates the analysis of the stability of the lateral collateral ligament. Arthrography is only used to determine the presence or absence of prosthetic loosening after TKA and is more accurate in diagnosing tibial prosthetic loosening than femoral prosthesis. The role of nuclear scanning in the postoperative evaluation of TKA is uncertain. The most commonly used are 99Tc-HDT, gallium citrate,111 indium-labeled leukocytes, and colloidal sulfur (Sulfur Colloid) bone marrow scans. Most nuclear scans have high sensitivity but poor specificity. the Rand study showed a sensitivity of 83%, specificity of 85%, and diagnostic accuracy of 84% [15]. In rheumatoid arthritis or massive osteolysis, there are occasional false positives. Negative nuclear scan results can exclude infection and loosening. Nuclear uptake of 99Tc increases for some time after artificial arthroplasty, and it is only 6-12 months after hip arthroplasty that 99Tc uptake returns to normal levels, and Rosenthal et al. reported that 89% of tibial prostheses and 63% of femoral prostheses exhibit increased 99Tc uptake 1 year after TKA. Therefore, the application of 99Tc alone is not sufficient to determine the presence of infection after TKA [17].Dannis Dogllas recommended first using a 99Tc-HDP scan and then performing a nuclear scan with labeled leukocytes if the results are positive but the presence of infection cannot be determined [18]. In contrast, Henry D. Clarke recommended a combination of three nuclear scans to identify infection, aseptic loosening, reflex sympathetic dystrophy, and periprosthetic stress fractures, as the combination can increase the accuracy of infection diagnosis to more than 95%. CT is more helpful than conventional imaging in determining the location and extent of osteolysis and prosthetic rotational alignment. ct examination is superior to patellar and femoral prostheses for the diagnosis of periprosthetic osteolysis of the tibial prosthesis. MRI using software that eliminates metallic artifacts is better than CT for the diagnosis of periprosthetic osteolysis after TKA, but it has not been widely promoted and used in clinical practice.