Temperature Sensitive Release of PGE2 and Diminished Energy Requirements in Synovial Tissue With Postoperative Cryotherapy - A Prospective Randomised Study After Knee Arthroscopy

Abstract Background: Local external cooling of the postoperative field is a treatment paradigm aiming for enhanced recovery after joint surgery. It is supposed to reduce pain and improve mobilization, enabling same day surgery. Hypothesis: Systematic postoperative cooling and compression after knee arthroscopy will reduce pain and also be reflected by changes in local levels of metabolic and inflammatory variables in the synovial membrane. Study design: Prospective randomised study; Level of evidence 1. Methods: Forty-four otherwise healthy patients were included in the study and randomised to systematic cooling and compression or NO cooling and compression after knee arthroscopy. Microdialysis of the synovial membrane was performed postoperatively with measurements of PGE2, glucose, lactate, glycerol, glutamate and blood flow (ethanol exchange ratio). Local temperature was monitored as well as postoperative pain (VAS and NRS). Results: The application of a cooling and compression device after knee arthroscopy resulted in significantly lower temperature in the operated knee (skin, joint capsule and intraarticularly). The cooling and compression diminished energy requirements in synovial tissue and a 3 temperature sensitive influence on inflammation (PGE2) were shown. No effect on postoperative pain was detected. Conclusion: Local cryotherapy and compression after knee arthroscopy significantly lowered local knee temperature postoperatively. A correlation with synovial PGE 2 and temperature was shown. Since PGE2 is a pain and inflammatory marker this implicates a positive anti-inflammatory effect induced by postoperative local cooling and compression. Hypothermia is proposed to have a protective effect in ischemic tissue. This is probably due to a decreased metabolic rate and therefore decreased energy requirements as shown by stable levels of lactate despite lower blood flow indicated by increasing ethanol ratio.