Dexamethasone as adjuvant for femoral nerve block following knee arthroplasty: a randomized, controlled study.

BACKGROUND: We examined the effect of the addition of dexamethasone to bupivacaine for femoral nerve blocks on the block duration and the quality of post-operative analgesia following total knee replacement surgery.

METHODS: In total, 200 ASA I-III patients were randomly allocated to either the control group who received bupivacaine 0.5% or the dexamethasone group who received bupivacaine 0.5% plus 8 mg dexamethasone for the femoral nerve block, followed by a continuous perineural bupivacaine infusion started at the time of block resolution. Patients were assessed for the duration of analgesia by the return of pinprick sensation and the 24-h morphine consumption as the primary outcomes of the study. A numerical rating scale from 0 to 10 was used to assess post-operative pain at zero, ½, 2, 6, 24, 48, and 72 h.

RESULTS: There was no difference between groups in either sensory or motor block onset; however, the duration of the block was significantly prolonged in the dexamethasone group, 25.7 ± 3 h, vs. 18.8 ± 4 h in the control group P < 0.0001. The total morphine consumption was not different between groups, but the dexamethasone group consumed less morphine in the first 6 h post-operatively. The addition of dexamethasone improved pain control on the first post-operative day, but no difference in the pain score was detected on days 2 or 3.

CONCLUSION: The addition of dexamethasone to bupivacaine for femoral nerve block prolonged the duration of analgesia, improved early post-operative pain following total knee arthroplasty.