Temperature-sensitive release of prostaglandin E₂ and diminished energy requirements in synovial tissue with postoperative cryotherapy: a prospective randomized study after knee arthroscopy.

This article was updated on November 23, 2011, because of a previous error. In the Reference Section, the references that had previously been numbered 18, 19, and 20 are now numbered 17, 18, and 19, and reference 20 has been added. Background: Local external cooling of the surgical field after joint surgery is intended to enhance recovery and to facilitate the use of outpatient surgery by reducing pain and improving mobility. We hypothesized that the effects of postoperative cooling and compression after knee arthroscopy would be reflected in changes in the concentrations of metabolic and inflammatory markers in the synovial membrane. Methods: Forty otherwise healthy patients who were to undergo knee arthroscopy were included in the study, and half were randomized to receive postoperative cooling and compression. Microdialysis of the synovial membrane was performed postoperatively, and the concentrations of prostaglandin E2 (PGE2), glucose, lactate, glycerol, and glutamate as well as the ethanol exchange ratio (which indicates blood flow) were measured. The temperature of the knee was monitored, and postoperative pain was assessed by the patient with use of a visual analog scale, a numeric rating scale, and the need for rescue medication. Results: Application of the cooling and compression device after knee arthroscopy significantly lowered the temperature in the operatively treated knee (as measured on the skin, within the joint capsule, and intra-articularly). The cooling and compression appeared to decrease inflammation, as indicated by a temperature-sensitive decrease in the PGE2 concentration. The hypothermia also decreased the metabolic rate of the synovial tissue and thus decreased energy requirements, as shown by the stability of the lactate concentration over time despite the decreased blood flow that was indicated by the increasing ethanol exchange ratio. No effect of the compression and cooling on postoperative pain was detected. Conclusions: Local cryotherapy and compression after knee arthroscopy significantly lowered the temperature in the knee postoperatively, and the synovial PGE2 concentration was correlated with the temperature. Since PGE2 is a marker of pain and inflammation, the postoperative local cooling and compression appeared to have a positive anti-inflammatory effect. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.