Prostaglandin E2 production in synovial tissue and acute postoperative pain after knee arthroscopy.

Postsurgical inflammation leads to sensitisation of "sleeping" nociceptors, which enhance pain perception and induce hyperalgesia. Prostaglandin E2 plays a central role in this process. Synovial microdialysis technique allows analyses of biological markers of local inflammation simultaneous with a close follow up of the patient's pain experience. Tissue injury (or surgery) initiates liberation of inflammatory mediators and hyperalgesic substances. This project is translational and aims at exploring the relationship between perceived acute postoperative pain and inflammation. Microdialysis of synovial tissue and pain score after arthroscopy is of special interest to study since the natural pain course and the local inflammation can be observed in patients with no analgesic therapy. Methods This is a clinical observational study of local inflammatory mediators and perceived pain in patients undergoing knee arthroscopy in general anesthesia with propofol, remifentanil and fentanyl. Microdialysis of the synovial membrane was performed in all patients every 20 min for 140 min postoperatively (seven samples). At the same intervals PGE2 was measured and correlated with patients report of pain intensity on a 0-100mm visual analogue scale (VAS). Results Five patients (1 female, 4 male) who did not receive any non-steroidal antiinflammatory drugs or paracetamol were included. The pain intensity was 1-34mmVAS and the PGE2 levels were from 293 pg/ml to 5818 pg/ml. Maximum pain score (mean 23 and SD 12mm VAS) and PGE2 levels (mean 2026 pg/ml and SD 1380 pg/ml) occurred about 40 min after surgery. Correlation analysis shows a significant correlation (R = 0.48, p = 0.004). Conclusion This pilot study indicates a positive correlation between postoperatively perceived pain and local PGE2 concentration.