Objective To differentiate between peri-prosthetic infection and aseptic loosening using quantitative analysis of triphasic bone scintigraphy.Methods Twenty-eight patients (9 males,19 females; mean age 67.5 years,range 49-80 years) with recurrent joint pain after arthroplasty were retrospectively assessed.All patients underwent triphasic bone scintigraphy.ROI of each joint was drawn and the ratios of affected to unaffected side were calculated.The ratios of blood flow phase,blood pool phase,static phase,Creactive protein (CRP) and erythrocyte sedimentation (ESR) were quantitatively analyzed by ROC curve.The final diagnosis was based on microbiological and histological examinations.The optimal cut-off value was chosen based on the ideal sensitivity and specificity.Results Nine patients were diagnosed as septic loosening,17 patients aseptic loosening,1 patient bursitis of hip joint and 1 patient suture reaction.Taking the positive results of blood flow phase or blood pool phase as standard for diagnosing septic loosening,the sensitivity,specificity and accuracy of bone scintigraphy were 7/9,78.9％ (15/19) and 78.6％ (22/28),respectively.The AUC of blood pool phase was 0.942,and the sensitivity and specificity were 8/9 and 78.9％(15/19),respectively,with the optimal cut-off value of 1.40.The AUCs of blood flow ratio and CRP were 0.816 and 0.795,with cut-off values of 1.53 and 1.20,respectively.The AUCs of static phase ratio and ESR were 0.474 and 0.722,respectively,both P＞0.05.Conclusions For the diagnosis of septic loosening,quantitative analysis of triphasic 99Tcm-MDP bone scintigraphy,particularly with the ratio of blood pool phase,is more accurate than qualitative analysis.