The issue of rare diseases has become a public health priority. In France, a national plan for rare diseases was published in 2004. It leads to the creation and certification of numerous Rare Disease Reference Centers by the French National Authority for Health (Haute Autorité de Santé).

Our Fibrous Dysplasia Reference Center has been certified since 2006. However, evaluating the mechanical strength and fracture risk of fibrous dysplasia lesions remains a major unresolved challenge for clinicians. Improving the assessment of fracture risk therefore represents a key clinical objective.

Inclusion Criteria:

• Adults with Fibrous Dysplasia (FD) of the bone or McCune-Albright Syndrome (MAS);
• who have received care at the center through outpatient consultation, multidisciplinary evaluation, or hospitalization;
• whose diagnosis was confirmed by an expert physician from the reference center based on a combination of clinical, biochemical, and radiological criteria, in accordance with the recommendations of the international FD/MAS consortium (Javaid MK et al., Orphanet J Rare Dis. 2019);
• for whom a histological confirmation was obtained in cases of diagnostic uncertainty;
• no objection to data collection

Exclusion Criteria:

• - CT scan with implanted material on the femur,
• Individuals under legal protection measures

Clinical data issued from Easily HYBRID DF Database, and CT images of long bones acquired during routine clinical care and retrieved from the HCL imaging..