The Effect Of Dexmedetomidine As Adjuvant To Ropivacaine 0.1% For Femoral Nerve Block On Strength Of Quadriceps Muscle In Patients Undergoing Total Knee Arthroplasty: A Double-Blinded Randomized Controlled Trial

Background: Femoral nerve block (FNB) has been considered as an excellent analgesic modality in total knee arthroplasty (TKA) pain control. However, relatively high concentration of ropivacaine could lead to quadriceps muscle weakness and increase the risk of postoperative falls. Objective: This double-blinded randomized controlled study was designed to investigate the effect of a combination of dexmedetomidine with a lower concentration of ropivacaine on quadriceps muscle strength and analgesic effect in FNB. Methods: A total of 90 patients scheduled for TKA were randomized to receive continuous FNB postoperatively using 0.2% ropivacaine (H group), 0.1% ropivacaine (L group) or 0.1% ropivacaine combined with 2 mu g/kg dexmedetomidine (LD group). Meanwhile, intravenous patient-controlled analgesia with morphine was administered to patients. The primary endpoint was the strength of quadriceps muscle evaluated by manual muscle testing (MMT) and Timed Up and Go test (TUG). The secondary endpoint was the pain scores and morphine consumption among different groups. Results: For MMT, LD group showed higher quadriceps muscle strength than the other two groups (P<0.05) at 12 hrs postoperatively. TUG test was conducted to measure the walking ability, and showed that scores were significantly better in LD group than those in H group and L group (P<0.05) at 24 and 48 hrs postoperatively. There was no significant difference between H and LD group in the numeric rating scales (NRS) scores both at rest and at 45 degrees flexion. The total morphine consumption in L group was significantly higher than in H or LD group (P<0.001). Conclusion: Collectively, the addition of dexmedetomidine 2 mu g/kg to 0.1% ropivacaine preoperatively would preserve quadriceps muscle strength with satisfactory analgesia in patients undergoing TKA.