Joint Status in Subjects With Severe Hemophilia A in Relation to Different Treatment Regimens

Inclusion Criteria: * Males aged 12 - 35 years * Severe hemophilia A ( \< 1 % FVIII:C) * No history of Factor VIII inhibitory antibody * For prophylaxis groups, having received at least two prophylactic infusions per week for 45 weeks per year for the prevention of bleeding without relevant interruption and continuing until the present. * Complete documentation of joints bleeds and their locations prior to start of prophylaxis, * Bleeding history and/or treatments received during the last 5 years documented in the subjects medical records. * For the on-demand subjects \> 12 bleeds/year in the last 5 years. * Written informed consent by subject and parent/legal representative, if \< 18 years Exclusion Criteria: * Individuals with other coagulopathies (e.g., von Willebrand disease) * HIV seropositive subjects * Individuals for whom the most clinically severe joint is not one of the 4 index joints (ankle, knee) * HCV seropositive individuals who underwent interferon therapy during the last 12 months * Individuals for whom high-magnetic exposure is contraindicated (see section 7.1) * Synovectomy performed within the six months prior to investigation enrollment or orthopedic surgery planned to be performed within the investigation period * Joint replacement * For the on-demand treatment group, any period greater than 8 consecutive months having received \>/= 50 IU per kg per week Factor VIII for the prevention of bleeding