Abstract. Introduction. Articular cartilage degradation is a defining feature of osteoarthritis. Synovium is a reactive tissue with synovial villae, neoangiogenesis and intimal hyperplasia common to many joint pathologies. The consequences of cartilage debris in osteoarthritis impacting the synovial intima is not well understood. We analysed the immunohistology of synovium from 16 patients with osteoarthritis and 17 patients undergoing knee surgery for non-arthritic pathologies. This data was integrated with imaging and functional scores to correlate synovitis in osteoarthritis. Methodology. Formalin-fixed paraffin embedded synovial biopsy sections were cut in serial sequence and processed for routine staining (H&E or CD3, CD68, CD20, Vimentin, vWF and PCNA IHC) using standardised Dako monoclonal mouse anti-human antibodies. Digital images scanned at x20 were evaluated for fragments of cartilage and aggregates of inflammatory cells. Clinical data (gender, BMI, KL grade, WOMAC & SF-12 scores) was aligned with histopathological data. Results. Cartilage fragments were seen in the synovial intimal layer from end-stage osteoarthritis especially those with BMI<30kg/m2. Macrophages, T-cells and B-cells were identified surrounding cartilage inclusions. Inflammatory aggregates of T-cells, B-cells and macrophages were located peri-cartilage in the intima and peri-vascular in the sub-intimal layer of the synovium. Worse synovitis and function scores were significantly associated with both cartilage inclusions and inflammatory aggregates. X-ray features linked to longer duration of symptoms were associated with inflammatory aggregates. Conclusion. The histological features of the synovium clearly reflect deteriorating joint structures and compromised clinical function