Postoperative analgesia for elective total knee arthroplasty under subarachnoid anesthesia with opioids: comparison between epidural, femoral block and adductor canal block techniques (with and without perineural adjuvants). A prospective, randomized, clinical trial.

Background: Optimal control of acute postoperative pain and prevention of chronic persistent pain in total knee arthroplasty (TKA) remain a challenge. The main hypothesis was that nerve blocks improve postoperative analgesia especially if perineural adjuvants are added.

Methods: Immediate postoperative pain (24 hours) was evaluated every hour in 639 patients using a verbal rating 11-point scale for patient self-reporting of pain (VRS-11). All patients received subarachnoid anesthesia and were randomly allocated in 8 groups: control group, epidural (EA) and single shots femoral (FNB) or adductor canal blocks (ACB), both with and without adjuvants: dexamethasone (+Dexa) or dexmedetomidine (+Dexm). Patients received intravenous analgesia (metamizole magnesium, dexketoprofen) and rescue analgesia when needed, intravenous (paracetamol and morphine) and/or regional (epidural boluses, femoral and sciatic nerve blocks). Demographics, orthopedic knee scores and adverse effects were also recorded.

Results: A 45.2% of patients had no immediate postoperative pain (P=0.0001). Rescue analgesia was needed in 48.8% of patients (P=0.0001): control group 72.8% of patients, EA 51.9%, FNB 40.0%, FNB+Dexa 33.3%, BNF+Dexm 41.3%, ACB 51.9%, ACB+Dexa 38.3% and ACB+Dexm 61.5% respectively. There were also differences in the total postoperative time without pain (P=0.0001), with mild (P=0.0001) or moderate pain (P=0.001) but not with severe pain (P=0.119).

Conclusions: Peripheral nerve blocks with perineural dexamethasone improve postoperative analgesia for TKA. The addition of dexamethasone to adductor canal block open new possibilities to improve analgesia for TKA, and should be investigated as an alternative to femoral nerve block.