52 patients undergoing primary total knee arthroplasty (TKA) were randomly assigned to receive a transdermal fentanyl patch (TFP; 12.5ug/h) in conjunction with non-steroidal anti-inflammatory drugs (NSAIDs) or NSAIDs alone for the management of post-operative knee pain. The purpose of this study was to investigate the effect of a transdermal fentanyl patch on pain and function up to 14 days following surgery. Patients receiving treatment with a TFP patch demonstrated greater reduction in VAS pain on movement and greater muscle strength recovery at 14 days compared to patients receiving NSAIDs alone. No significant difference in adverse events (nausea and constipation), VAS pain at rest, or knee range of motion at 14 days was observed between groups.