Buprenorphine versus dexamethasone as perineural adjuvants in femoral and adductor canal nerve blocks for total knee arthroplasty: a randomized, non-inferiority clinical trial.

Background: Optimal control of acute postoperative pain and prevention of chronic persistent pain in total knee arthroplasty (TKA) remain a challenge.
Methods: A randomized, non-inferiority clinical trial (385 patients) evaluated every hour immediate postoperative pain during 24 h, using a verbal rating 11-point scale for patient self-reporting of pain (VRS<inf>11</inf>). All patients received subarachnoid anesthesia and were randomly allocated in four groups: single shots femoral (FNB) or adductor canal blocks (ACB), both with dexamethasone (dex) and buprenorphine (bup). Patients received intravenous analgesia (metamizole magnesium, dexketoprofen) and rescue analgesia when needed: intravenous (paracetamol and morphine) and/or regional (femoral and sciatic nerve blocks). Demographics and adverse effects were also recorded.
Results: A 45.7% of patients had pain: bupACB 56.3%, bupFNB 50.0%, dexACB 40.6% and dexFNB 36.1% (P=0.022). Rescue analgesia was needed in 37.7% of patients (P=0.128). There were statistical differences in percentage of timepoints without pain (95.0±7.9%, P=0.014) and mean VRS<inf>11</inf> (0.18±0.3, P=0.012) but no differences in distribution of intensity periods of pain. There were no significant differences in the need of rescue analgesia excepting the use of intravenous morphine (P=0.025).
Conclusions: Buprenorphine is in the present trial inferior to dexamethasone by less than the established non-inferiority limit when used as perineural adjuvant in femoral nerve or adductor canal blocks in total knee arthroplasty analgesia. So, it could be considered an alternative in patients where dexamethasone is contraindicated, such as diabetics.