Total knee replacement is an effective method to treat end-stage osteoarthritis. However, post-operative pain is still a bothering problem. Pre-emptive analgesia is defined as an antinociceptive treatment which prevents pain before its onset. Preoperative analgesia is thought more effective than an equal post-operative dose. Surgical trauma induces the synthesis of prostaglandins, which sensitize the peripheral nociceptors.Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis both in the periphery and the spinal cord, therefore decreasing the post-operative hyperalgesic state.