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) 1β, IL‐6, IL‐8, IL‐10 and tumour necrosis factor α (TNF‐α) 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 (ρ = .284, p = .024). Synovial tissue cytokines correlated strongly to inflammation‐related factors: diagnosis (IL‐1β, p = .001; TNF‐α, p = .000; IL‐10, p = .000), TMJ palpation pain (IL‐1β, p = .024; TNF‐α, p = .025), synovitis score (IL‐1β, p = .015) and subjective TMJ pain (TNF‐α, 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.