Prospective Study on the Consequences of Weight Loss After Bariatric Surgery on Obese Patients' Spine.

Inclusion Criteria: * Age \> 18 years old * BMI \> 40 or BMI \> 35 with comorbidities due to obesity ( criteria for bariatric surgery) * Follow up in Pompidou's Hospital Nutrition service * Bariatric surgery intervention ( Sleeve gastrectomy or By pass) * Follow up possible for one year or more * Being covered by French social insurance * Consent to participate in the study Exclusion Criteria: * History of spine surgery * Bariatric surgery postoperative complication * Non mastering of french language * MRI contraindication * Patient under legal protection ( e.g. guardianship)