Dexamethasone vs. Dexmedetomidine as Adjuvants to Erector Spinae Plane Block in Total Knee Arthroplasty: A Randomized Double-Blind Controlled Trial

Background: Total knee arthroplasty is associated with significant postoperative pain. The erector spinae plane block (ESPB) is increasingly used as part of multimodal analgesia, but its duration may be limited. Adjuvants such as dexamethasone and dexmedetomidine may enhance analgesic efficacy; however, direct comparisons between these agents in ESPB remain limited. Methods: In this prospective, randomized, double-blind trial, 90 patients undergoing total knee arthroplasty were allocated to receive ESPB with ropivacaine alone (control), with ropivacaine plus dexamethasone (DEX), or with ropivacaine plus dexmedetomidine (DEM) (n = 30 per group). The primary outcome was time-to-first opioid requirement within 48 h. Secondary outcomes included total opioid consumption, postoperative pain intensity (NRS), and adverse events. Time-to-event analysis was performed using Kaplan–Meier and Cox regression. Results: Time-to-first opioid requirement was significantly prolonged in both DEX and DEM groups compared with control (log-rank p < 0.0001). Median time was 7.85 h (95% CI 7.40–8.50) in control, 13.70 h (12.80–14.50) in DEX, and 12.40 h (11.20–14.30) in DEM. Both DEX (HR 0.036, 95% CI 0.017–0.079) and DEM (HR 0.058, 95% CI 0.028–0.121) significantly reduced the hazard of opioid requirement (p < 0.0001). Total opioid consumption was significantly lower in the DEX group compared with both control and DEM (p < 0.0001), while no difference was observed between DEM and control. Pain scores were lower in the DEX group in the early postoperative period. No statistically significant differences in adverse events were observed between groups. Conclusions: Both dexamethasone and dexmedetomidine prolong ESPB analgesia in total knee arthroplasty. However, dexamethasone provides superior analgesic efficacy without increasing adverse events.