The aim of this study is to determined the smallest significant value in osteodensitometry in obese population. The study population will be divided in 3 groups according to their BMI.

Bone mineral density will be measured twice in osteodensitometry, then the smallest significant value will be determined.

Our hypothesis is that the smallest significant value that we use in an non-obese population can be different in an obese population.

The aim of this study is to determined the smallest significant value in osteodensitometry in obese population.

There will be at least 120 patient included. The study population will be divided in 3 groups according to their BMI : the first group has a BMI between 30 and 35 kg/cm² ; the second group has a BMI between 35 et 40 kg/cm² ; and the third group has a BMI over 40 kg/cm².

Patients will be referred by their doctors (rheumatologist and others) to evaluate their bone mineral density in osteodensitometry at CHU of Reims. Patients will be informed of the aim of the study by the prescriptor of the osteodensitometry.

The osteodensitometry will be executed by a nurse. Patients will have to complete a questionnaire about their medical history and their medications.

Bone mineral density will be measured twice in osteodensitometry, at the lumbar spine, the hip and the femur. This exam lasts approximately 40 minutes.

Then the smallest significant value will be determined by comparing each measure for every patients.

Inclusion criteria :

• Major patients
• Patients referred to the CHU of Reims to make an osteodensitometric evaluation of their bone mineral density
• BMI > 30 kg/cm²
• Patient affiliated to a health insurance plan
• Patients who have signed informed consent

Exclusion criteria :

• Minor patients
• Pregnant women
• Patients protected by the law