MMP13 and hemarthrosis: We found that during hemarthrosis, nuclear factor kappa B (NF-κB), a key stress-responder and inflammatory mediator and other molecular markers of hypoxia (hypoxia inducing factor 1α (HIF-1α) and HIF-2α), angiogenesis (vascular epithelial growth factor α (VEGF-α)) and chondro-degenerative matrix-metalloproteinases 3 (MMP3) and MMP13 play a progressive role in the development of arthropathy.