Hemophilia is an X-linked recessive genetic disorder caused by deficiency of clotting factors which primarily affects males. It is characterized by recurrent spontaneous and trauma-related bleedings, with a majority of spontaneous bleedings occurring in synovial joints (i.e. hemarthrosis). Thanks to tremendous scientific progress, patients with hemophilia (PwH) in developed countries benefit from excellent access to substitution therapy (i.e. clotting factor substitution by intravenous injection) which is administered after a hemorrhage or as prophylactic treatment, thereby considerably decreasing the risk of bleedings. As a result life expectancy of treated PwH has now become comparable to the general population. However, despite adequate prophylactic replacement therapy, recurrent joint bleedings still occur. These bleedings have devastating effects on joint components due to iron deposits and inflammation in the joint, resulting in synovial inflammation, cartilage degeneration and bone damage, with as end-stage a very painful and invalidating hemophilic arthropathy¹ affecting the majority of adult PwH. Indeed, joint pain has been reported as a major problem by PwH.

Therefore, haemophilia in adults seems clinically more related to a musculoskeletal disorder than a bleeding disorder, with many patients reporting a pain intensity exceeding 6/10 on a visual analogue scale. However, although the complexity of joint pain has been studied in chronic joint pain conditions such as low back pain, osteoarthritis or rheumatoid arthritis, until present only very limited research has been done on joint pain within PwH. Therefore, exploring the underlying mechanisms and the functional implications of this intense joint pain is urgently needed. As such, the main aim of the current proposal is to gain more insights in joint pain in PwH enabling us to move towards adequate pain management in PwH. As the majority of studies in chronic joint pain conditions has shown that the biopsychosocial perspective is crucial in pain management, we aim to base the assessment on the Outcome Measures in Rheumatology initiative (OMERACT).