Background and objectives Total knee arthroplasty is associated with significant pain, and effective analgesia is beneficial to patient satisfaction and functional outcomes. Studies have demonstrated that dexamethasone may have a facilitatory role on the action of local anesthesia, but this effect, when added to a local infiltration analgesia (LIA) mixture for patients having knee arthroplasty, is underexplored. Our hypothesis was that the addition of dexamethasone to local anesthetic infiltration would improve analgesic outcomes following total knee arthroplasty.

Methods We performed a double-blind, randomized controlled trial of 140 patients undergoing elective, unilateral, total knee arthroplasty. Patients were randomly allocated to receive either 2 mL of saline 0.9% or 2 mL of dexamethasone 4 mg/mL added to a LIA mixture. Our primary outcome was 24 hours of oral morphine equivalent consumption. Our secondary outcomes included short-term and long-term analgesic and functional outcomes and adverse events.

Results A total of 72 patients were included in the saline group and 68 were included in the dexamethasone group. We found comparable 24 hours of morphine consumption between saline and dexamethasone groups, with a median of 60 (IQR 40–105 (range 16–230)) mg and 56 (IQR 41–75 (range 0–300)) mg, respectively (p=0.096). Dexamethasone was associated with a statistically significant reduction in total inpatient opioid consumption, incidence of requiring rescue patient-controlled analgesia, length of hospital stay, and postoperative nausea, compared with saline. Patients in the dexamethasone group had a greater range of joint movement and distance walked on postoperative day 1 than the saline group. There were no differences in rest or active pain scores, timed up and go or 3-month outcomes.

Conclusions Dexamethasone 8 mg was associated with no improvements in 24 hours of morphine consumption but was associated with modest improvements in short-term analgesia, short-term function, length of stay and postoperative nausea. There were no long-term benefits in the use of dexamethasone in LIA for patients undergoing total knee arthroplasty.

Trial registration number NCT02760043