Predicting acute postoperative pain by thermographic imaging and saliva prostaglandin E2 levels in male patients undergoing knee arthroscopy
Louise Skou Nielsen, Siv Sofie Christensen, Eva Szuchy Kristiansen, Sten Rasmussen, and Parisa Gazerani

Orthopaedic Surgery Department, Aalborg University Hospital, Denmark
Department of Biomedicine, Faculty of Medicine, Aalborg University, Denmark

Background and aims
In the acute postoperative period 30% of patients report moderate to severe pain. These patients are at higher risk of developing chronic postoperative pain. Identification of patients who are at risk for developing acute postoperative pain is important to achieve improved pain management after surgery. The aim of this study was to investigate whether preoperative average surface temperature on the knee and saliva prostaglandin E2 (PGE2) concentration could predict acute postoperative pain. 

Methods
Twenty-four men (18-48 years) who underwent elective knee arthroscopy participated in three consecutive sessions. Session 1 was conducted preoperatively, session 2 1.5 hours postoperatively, and session 3 one day postoperatively. Knee pain at rest was rated on a visual analog scale (VAS). The average surface temperature on each knee was assessed by thermographic imaging and saliva PGE2 concentrations were determined by enzyme-linked immunosorbent assay (ELISA).

Results
Surface temperature on the knee and saliva PGE2 concentrations were affected by knee arthroscopy (p<0.05). The average surface temperature on the operated knee dropped 1.92 ºC 1.5 hours after operation and increased with 3.84 °C one day after operation. Preoperative surface temperature on the knee did not show a correlation to acute postoperative pain (p>0.05). However, preoperative PGE2 concentrations were correlated to acute postoperative pain (p<0.05).

Conclusions
Knee arthroscopy affected the surface temperature on the knee and the saliva PGE2 concentration.  This preliminary study showed that PGE2 concentration measured preoperatively could predict acute postoperative pain in male patients undergoing knee arthroscopy.

PREDICTING ACUTE POSTOPERATIVE PAIN IN KNEE ARTHROSCOPY BY THERMOGRAPHIC IMAGING AND EVALUATION OF SALIVARY LEVELS OF PROSTAGLANDIN E2