While the duration of renal transplant function has increased over the last decade kidney transplanted patients (KTP) still exhibit a fracture risk 4 times higher than in the general population. Fracture risk remains increased despite the improvement of immunosuppressive therapies (IST) that allowed the reduction of steroid administration. Potential explanations for this could be 1) that Chronic Kidney Disease (CKD) induces renal osteodystrophy that occurs before kidney transplanted, impairs bone metabolism and promotes bone fragility ; 2) that kidney transplanted patients are older and older (14% of kidney transplanted patients were older than 70 in 2011 in France), ageing being a major risk factor for fractures 3) IST, besides steroid, may have deleterious effects on bone and 4) that secondary hyperparathyroidism, a risk factor of fractures, persists after kidney transplanted . Thus, the pathophysiology and epidemiology of bone fragility of kidney transplanted patient remains insufficiently characterized. Despite these data, and contrarily to what is done for patients candidates for cardiac transplantation, there is no general consensus for performing bone evaluation before kidney transplanted . Thus it's necessary to individualize the management of bone fragility and prevent fractures according to strategies that remain to be defined, provided that patients at risk are better detected.

Bone fragility is determined by quantitative parameters (bone mass) and qualitative parameters including macro- and micro-architecture (especially cortical porosity and thickness). The Dual Energy X-ray Absorptiometry (DEXA ) measurement of Bone Mineral Density (BMD) is a robust predictor of fracture risk in the non-uremic population. Micro and macro-architecture can be measured with High Resolution peripheral micro Computerized Tomography (HRpQCT) at the ankle and the wrist . Some recent studies suggested that HRpQCT could be a better fracture predictor than DEXA in uremic populations. In this context, the aim of our project is to describe in a cross sectional study the bone status of CKD patients, candidates for kidney transplanted . It will be 1) calculated the prevalence of cortical osteoporosis as assessed by cortical thickness at the ankle and the wrist (primary end point), 2) analyzed other HRpQCT microarchitecture quantitative parameters and 3) defined the biological and clinical factors associated with bone degradation (secondary endpoints). This population will be compared to age and sex matched normal subjects (collaboration with Pr Rizzoli, Geneva, Switzerland). The DEXA and HRpQCT will be compared for detection of patients at risk for fracture.

Inclusion Criteria:

• Serum parathyroidal Hormon (PTH ) > 65pg/ml
• Stage 5 or 5D Chronic Kidney Disease patients
• Patient registered (or on the verge of being registered) on the KT waiting list at St-Etienne Hospital, France
• Written consent of patient

Exclusion Criteria:

• none

patient with end stage renal disease