Inclusion Criteria:  Patients:  Men aged 20 to 60 years Severe hemophilia A or B (FVIII or FIX<1%) Regular followed up in Lyon Hemophilia Center Ability to give free and informed consent Person capable of actively participating in radiological examinations  Healthy Mens:  Aged 20 to 60 years  Exclusion Criteria:  Women Not covered by health system Vulnerable (adults unable to consent, protected under guardianship, prisoner) Any blood coagulation abnormality other than severe hemophilia A or B Having one of the following treatments against osteoporosis of more than 6 months : bisphosphonates, denosumab, teriparatide With a chronical disease having a high impact on bone structure and no related to hemophilia disease, such as Cushing or Crohn diseases.