There is extravasation of erythrocytes and leucocytes. As the erythrocytes break down, haemoglobin and iron are released, which when minimal can be phagocytized by the synovial macrophage-like cells and sequestered. Within 1 week, blood in the joint, if not excessive, is resorbed by these synovial lining cells and subsynovial macrophages, resulting in full haemorrhage resolution [44]. If recurrent, or a massive episode of bleeding occurs, these cells are overwhelmed, and components of blood, such as iron, remain in the joint space and bathe cartilage surfaces. The role of haemoglobin and iron, specifically, has not

been clearly elucidated [45], although the possibility of aberrant gene expression has been suggested [46,47] and formation click here of reactive oxygen intermediates may play a role [40]. There is hypertrophy and hyperplasia of synovial Volasertib solubility dmso cells due to severe or repeated bleeding episodes [48]. Like a growing tumour, synovial cells require oxygen and nutrients to survive, which are initially provided by diffusion. However, once the membrane grows beyond a few cell layers in thickness, hypoxia results, invoking an angiogenic stimulus, which when combined with proangiogenic inflammatory mediators, leads to neovascularization of the membrane.

This neovascularization facilitates expansion of the synovial membrane and results in frond-like projections of the membrane along the articular surfaces, which may lead to impingement and mechanical bleeding due to vascular disruption. Direct effects of blood on cartilage are also likely as described find more above. Once the process begins, the eventual outcome is evolution into a scar-like, fibrotic arthritis now known as haemophilic arthropathy. The pathobiology of this process remains to be established [49,50]. Although many tools have been developed to assess outcomes in haemophilia patients, the most critical outcome to assess is bleeding frequency. In the absence of bleeding and specifically haemarthrosis,

joint disease is unlikely, although subclinical bleeding has been proposed to explain the arthropathy that develops in the absence of recognized bleeding [51]. More sensitive tools are needed to detect the earliest signs of bleeding. Recently, considerable attention and resources have been devoted to the evaluation of MRI to detect the earliest signs of joint disease [52–57]. In the future, more sensitive imaging modalities may become available for clinical use, such as blood-oxygen-level-dependent functional MRI, ultrasmall superparamagnetic iron-oxide contrast-enhanced MRI, T1 and T2 mapping MRI, ultrasound biomicroscopy, microbubble contrast-enhanced ultrasonography and positron emission tomography [58]. Another potential modality to monitor subclinical bleeding and the earliest signs of joint disease is the use of biomarkers [59].