Objective To explore the effect of methylene blue combined with ropivacaine for sa-phenous nerve block on the postoperative analgesia in patients undergoing total knee arthroplasty.Methods Sixty patients were selected for elective TKA,24 males and 36 females,aged 60-75 years,BMI 18.5-30.0 kg/m2,ASA physical status Ⅱ or Ⅲ.The patients were divided into two groups using randomized nu-merical table method:methylene blue combined with ropivacaine group(group MR)and ropivacaine group(group R),30 patients in each group.Ultrasound-guided saphenous nerve block was performed with 0.10％methylene blue+0.25％ropivacaine composite 20 ml in group MR,and ultrasound-guided saphenous nerve block was performed with 0.25％ropivacaine 20 ml in group R before the combined spinal-epidural anesthe-sia.The VAS pain scores at rest and during activity at 6,12,24,48,and 72 hours postoperatively,the maximum range of motion mobility(ROM)of the knee joint of the affected limb,the quadriceps unarmed manual muscle test(MMT)scores at 24,48,and 72 hours postoperatively,the effective number of analge-sic pump presses,and the time of the first additional time of the remedial analgesic were recorded.The com-plications related to nerve block,such as bleeding,infection,local anesthetic poisoning,nerve injury,and peripheral tissue injury were recorded.Results Compared with group R,the VAS pain score at rest was significantly lower in group MR at 12,24,48,and 72 hours postoperatively(P＜0.05).Compared with group R,the VAS pain scores during activity were significantly lower in the group MR at 48 and 72 hours postoperatively(P＜0.05).Compared with group R,ROM of the knee joint of the affected limb was signif-icantly greater in group MR at 24,48,and 72 hours postoperatively(P＜0.05).The effective number of analgesic pump presses and the rate of remedial analgesia were significantly lower in the group MR compared with group R(P＜0.05).There were no complications related to nerve block during hospital stay in both groups.Conclusion Ultrasound-guided methylene blue combined with ropivacaine for saphenous nerve block can enhance the postoperative analgesic effect,prolong the duration of analgesia,reduce the use of postoperative analgesics,and facilitate the functional exercise of the knee joint in the early postoperative pe-riod.