Comparison of the postoperative analgesic effect of different-volume ropivacaine on adductor canal midpoint block for total knee arthroplasty

Objective To compare the postoperative analgesic effect and adverse reactions of different-volume ropivacaine during adductor canal (AC) midpoint block guided by ultrasound positioning in elderly patients after total knee arthroplasty (TKA). Methods A total of 90 patients who underwent elective unilateral knee replacement were enrolled. They were randomly divided into three groups (n=30): a ropivacaine 10 ml group (group A), a ropivacaine 20 ml group (group B) and a ropivacaine 30 ml group (group C). All patients underwent AC midpoint block guided by ultrasound after operation. Their VAS scores at rest and on movement at postoperative 6, 12, 24 and 48 h were recorded. Both groups were compared for 48 h cumulative dosage of sufentanil and dizocine, the quadriceps femoris muscle strength and active knee range of motion (ROM) before and after surgery, and the incidence of adverse reactions such as nausea and vomiting. Results Compared with group A, groups B and C showed remarkable decreases in VAS scores at rest and on movement at different time points after operation, cumulative consumption of sufentanil and dezocine at postoperative 48 h, and the incidence of nausea as well as vomiting, as well as increases in ROM at postoperative 24 h and 48 h (P<0.05). However, there was no statistical difference in the above parameters between groups B and C (P>0.05). Compared with group C, the muscle strength of the quadriceps femoris in groups A and B significantly increased at postoperative 24 h (P<0.05), but no statistical difference was found in the above parameter between groups A and B (P>0.05). Conclusions AC midpoint blocked with 0.375% ropivacaine at 20 ml can provide good postoperative analgesia for TKA, with little effect on quadriceps muscle strength, and promote the recovery of knee function after TKA.