Dynamic analysis of cytokine expression in synovial fluid after anterior cruciate ligament reconstruction surgery

Abstract

Purpose: Synovial fluid is an interstitial fluid secreted by fibroblast-like cells in the synovial membrane. It is a highly viscous liquid containing hyaluronic acid and various cytokines. The physiological functions of synovial fluid include reduction of friction, shock absorption, nutrient, and waste transportation in the joint. In addition, previous reports showed that mesenchymal stem cell-like cells, those are considered to contribute the tissue regeneration, reside in synovial fluid and the number of these cells increased after joint injury. These data strongly suggest that condition of synovial fluid may greatly influence joint homeostasis. This study aims the dynamic analysis of cytokine levels in synovial fluid after anterior cruciate ligament reconstruction surgery (ACL-R). Since ACL-R patients are regarded as a high-risk osteoarthritis (OA) group as it was reported that more than 30% of ACL-R patients develop radiographic OA on an average of 7.8 years after surgery, with most patients having no evidence of OA at the time of ACL-R, we expect that this study will give us critical information to identify prognostic factors for joint degeneration after injury. Methods: This study was approved by the Ethics Committee of this institute. All patients included in this study gave their full, written, informed consent for participation prior to the operative procedure. Synovial fluid was obtained from the patients who underwent ACL-R from January till August 2012 in our university hospital (Just before surgery, at day 3, at 3 weeks, and at 5 weeks post surgery: 26 samples, female: 13 male: 13, 14-62 year-old, average 30 year-old). Cytokine levels in synovial fluid were measured by ELISA (R and D systems, MN). In this report, we examined TNF-alpha and IL1-beta as pro-inflammatory cytokines and BMP7 as an anti-inflammatory and anti-catabolic factor for articular cartilage. Pearson's correlation coefficient test, Wilcoxon single-rank test, or Mann-Whitney's U-test were employed for the statistical analysis and values of p < 0.05 were considered significant. Results: Before ACL-R, average volume of synovial fluid was 7.6+/-7.2ml although it varied from individual patient (Max 15.5ml, Min 0.5ml). In all patients, synovial fluid volume surged around 3-fold at day 3 post surgery (average 21.6+/-8.0ml, Max 25ml, Min 7.8ml). In most patients, synovial fluid volume returned to the basal level within 3 weeks post surgery. Concentrations of TNF-alpha and IL1-beta were significantly increased at day 3 post surgery if compared to those at pre-operation (p<0.05). In addition, the concentration of TNF-alpha was positively correlated with the volume of synovial fluid at pre-operation (r=0.995, p<0.01) and day3 post-operation (r=0.535, p<0.05) while IL1-beta levels were not at any time point. Throughout the time point, BMP7 levels were very low and did not change significantly at pre- and post-operation. Surprisingly, BMP7 levels were positively correlated with IL1-beta levels at day 3 post-operation (r=0.59, p<0.01). These suggest that BMP7 may have subtle anti-inflammatory/anti-catabolic effect on cartilage at the acute inflammatory stage after joint injury. Conclusion: This is a longitudinal study of dynamic analysis of cytokine levels in synovial fluid from each patient undergoing ACL-R. In this report, we examined the levels of TNF-alpha, IL1-beta, and BMP7 in synovial fluid and observed that TNF-alpha levels were significantly correlated with the volume of synovial fluid.