Objective: To identify molecular biomarkers for early knee osteoarthritis (OA), we examined whether joint effusion in the knee associated with different gene expression levels in the circulation.Materials and Methods: Joint effusion grades measured with magnetic resonance (MR) imaging and gene expression levels in blood were determined in women of the Rotterdam Study (N=135) and GARP (N=98). Associations were examined using linear regression analyses, adjusted for age, fasting status, RNA quality, technical batch effects, blood cell counts, and BMI. To investigate enriched pathways and protein-protein interactions, we used the DAVID and STRING webtools.Results: In a meta-analysis, we identified 257 probes mapping to 189 unique genes in blood that were nominally significantly associated with joint effusion grades in the knee. Several compelling genes were identified such as C1orf38 and NFATC1. Significantly enriched biological pathways were: response to stress, gene expression, negative regulation of intracellular signal transduction, and antigen processing and presentation of exogenous pathways.Conclusion: Meta-analyses and subsequent enriched biological pathways resulted in interesting candidate genes associated with joint effusion that require further characterization. Associations were not transcriptome-wide significant most likely due to limited power. Additional studies are required to replicate our findings in more samples, which will greatly help in understanding the pathophysiology of OA and its relation to inflammation, and may result in biomarkers urgently needed to diagnose OA at an early stage.