40 patients scheduled to undergo total knee arthroplasty were randomized to a group that received transdermal fentanyl patches or to a placebo group to compare postoperative pain relief, rescue opiate requirements, active knee flexion, and incidence of side effects. Results indicated that postoperative VAS pain scores were significantly lower in the transdermal fentanyl patch (TFP) group from 2 hours to 72 hours postoperatively, when compared to the placebo group. Furthermore, rescue morphine consumption was also significantly less in the TFP group. Active knee flexion and incidence of side effects were similar between groups.