HIF1A and hemarthrosis: We had previously established that in the multiple injury model of hemarthrosis (Day 30/60/75/90), factors that contribute to hypoxia (HIF-1α, 3.3–6.5-fold), angiogenesis (VEGF-α, 2.5–4.4-fold) and chondrocyte damage (matrix metalloproteinase 13 (MMP13), 2.8–3.8-fold) were significantly elevated [7].