Synovial metabolism after knee joint arthroscopy : A microdialysis study

Abstract: Postoperative pain and swelling of the knee is a general finding after arthroscopy. In order to optimize and individualize the treatment it is of great importance to increase basic knowledge of perioperative local biochemical events in the synovial membrane. The present thesis explores metabolic and inflammatory changes in the synovial membrane after arthroscopy using microdialysis as monitoring technique. The first aim was to explore the basic changes in glucose, lactate, pyruvate, glycerol and blood flow in the synovial membrane after a standard arthroscopy without bloodless field. We also wanted to evaluate the microdialysis method in this field, as it has not been used in this tissue before. The second study was similar to the first but with bloodless field added and two reference tissues instead of one. Here we also wanted to study the general effects of the bloodless field. The third study was similar to the first with no bloodless field. Here we wanted to measure the effect of local addition of adrenaline on local metabolism and blood flow. In the fourth and last study we also monitored the above compounds and PGE2 and the relation to subjective pain. In all studies we performed a standard arthroscopy in general anaesthesia except in study II were we added bloodless field. The patients were monitored for 3 hours postoperatively with samples analyzed every 20 minutes after a 40 minute long equilibration period. Blood flow was analyzed using the ethanol escape method. In study III adrenaline was added to the perfusion solvent in one group and local anaesthetics with adrenaline was injected intraarticularly in a second grouo. A third group was used as reference. Lactate, glucose, glycerol and blood flow were monitored. In study IV we measured lactate, glucose, pyruvate, glycerol, PGE2 in relation to subjective pain measured as rescue opioid requirement. In study I there was a significant increase in lactate and a significant decrease in glucose indicating a local production of lactate and local consumption of glucose. In study II we found an increase in lactate over time in both bloodless synovium and thigh fat but not in contralateral reference thigh fat and a significant decrease in glycerol in bloodless fat over time and stable levels in synovium and contralateral fat. When adding adrenaline to the dialysis solvent in study III there was a 50 % decrease in glucose in the two examined tissues but no change in the other two experimental situations. Adrenaline to the dialysate solvent caused a -20 % transient increase in glycerol in the adipose tissue and a -20 % decrease in the synovial membrane. Intra articular injection of adrenaline caused approximately -20 % and -50 % increases in lactate in the synovial membrane. In study IV the concentrations of glucose and PGE2 were initially increased in the group requiring rescue opiods. In patients not requiring additional opioids the concentrations of glucose and PGE2 were unchanged throughout the experiment. Conclusions: Arthroscopic surgery causes a state of hypermetabolism with decreasing glucose and increasing lactate levels in the synovial membrane. Addition of bloodless field alters local carbohydrate metabolism in the synovial membrane and lipolysis in adipose tissue reflecting general effects apart from changes in local adipose tissue blood flow. This suggests that even minor surgical procedures cause important general metabolic and vascular responses. Catecholamines have pronounced in vivo effects on metabolism and blood flow in the synovial membrane. Pain after arthroscopy was reflected by increased glucose utilization and PGE2 production by the synovial membrane.