Cytokines in temporomandibular joint synovial fluid and tissue in relation to inflammation

Background Synovial tissue is known to be the origin of inflammation in joint disease. Despite this, synovial fluid is the main biological specimen of choice in temporomandibular joint (TMJ) inflammation and pathology biomarker research. No comparison of TMJ protein content between synovial fluid and synovial tissue has been made. Objectives The aim of this study was to investigate whether cytokine concentrations in synovial fluid can be related to cytokine concentrations in synovial tissue and to analyse correlation of clinical parameters reflecting local inflammation to cytokine concentrations. Methods Synovial tissue and fluid samples were obtained during the same surgical procedure from a cohort of 101 patients with TMJ disorders. Interleukin (IL) 1 beta, IL-6, IL-8, IL-10 and tumour necrosis factor alpha (TNF-alpha) were analysed in the samples and an intraindividual correlation made. Various patient-specific factors related to TMJ inflammation were associated with the cytokine concentrations in synovial fluid and tissue. Results No correlation between cytokine concentration in synovial fluid and synovial tissue was found, except for IL-8 (rho = .284, p = .024). Synovial tissue cytokines correlated strongly to inflammation-related factors: diagnosis (IL-1 beta, p = .001; TNF-alpha, p = .000; IL-10, p = .000), TMJ palpation pain (IL-1 beta, p = .024; TNF-alpha, p = .025), synovitis score (IL-1 beta, p = .015) and subjective TMJ pain (TNF-alpha, p = .016). Synovial fluid cytokines showed no significant relations to inflammation. Conclusions The investigated cytokine concentrations showed weak correlations between synovial fluid and synovial tissue, besides IL-8. Synovial tissue appeared to reflect inflammation to a higher extent than synovial fluid. Thus, suggesting that synovial tissue research should complement synovial fluid in future explorations of TMJ pathology and inflammation.

Automated summary

This study aimed to investigate the relationship between cytokine concentrations in synovial fluid and synovial tissue and analyze the correlation between clinical parameters reflecting local inflammation and cytokine concentrations. The results showed weak correlations between cytokine concentrations in synovial fluid and synovial tissue, except for IL-8. Synovial tissue seemed to better reflect inflammation, suggesting the need for further exploration of synovial tissue in TMJ pathology and inflammation research.