BACKGROUNDThere are several methods for postoperative analgesia for knee surgery. The commonly utilized method is multimodal analgesia based on continuous femoral nerve block. The aim of this study was to investigate the application of continuous adductor canal block for analgesia after total knee replacement and compare this method with continuous femoral nerve block.

METHODSSixty patients scheduled for total knee replacement from June 2013 to March 2014 were randomly divided into a femoral group and an adductor group. Catheters were placed under the guidance of nerve stimulation in the femoral group and under the guidance of ultrasound in the adductor group. Operations were performed under combined spinal and epidural anesthesia. After the operations, 0.2% ropivacaine was given at a speed of 5 ml/h through catheters in all patients. Visual analogue scale (VAS) pain scores at rest and while moving were noted at 4, 24, and 48 hours after the operation, and quadriceps strength was also assessed at these time-points. Secondary parameters such as doses of complementary analgesics and side effects were also recorded.

RESULTSThere were no significant differences between the groups in VAS pain scores at rest or while moving, at 4, 24, or 48 hours after the operation (P > 0.05). At these time-points, mean quadriceps strengths in the adductor group were 3.0 (2.75-3.0), 3.0 (3.0-4.0), and 4.0 (3.0-4.0), respectively, all of which were significantly stronger than the corresponding means in the femoral group, which were 2.0 (2.0-3.0), 2.0 (2.0-3.0), and 3.0 (2.0-4.0), respectively (P < 0.05). There were no significant differences between the groups in doses of complementary analgesics or side effects (P > 0.05). X-ray images of some patients showed that local anesthetic administered into the adductor canal could diffuse upward and reach the femoral triangle.

CONCLUSIONSContinuous adductor canal block with 0.2% ropivacaine could be used effectively for analgesia after total knee replacement. Compared with continuous femoral nerve block, this analgesic method has similar analgesic effects and is associated with less weakness of quadriceps muscle.