Obesity and back pain are massive public health problems, and the relationship between the two has not been described and studied. However, the investigators have also observed that many ex-obese patients still suffer from back and leg pain after an important weight loss.~The aim of this study is to measure the effect of weight loss on back pain, and to find out what parameters can explain such modifications (increasing or decreasing back pain).~The investigators will study clinical parameters, as well as radiological (to measure the effect of weight loss on spine sagittal alignment) and MRI (to measure lipomatosis, which is a fat epidural accumulation, responsible for nerve compression and therefore back and leg pain).
The purpose of this study is to determine how an important weight loss after bariatric surgery affects obese patients ' spine, and the effects it has on low back pain, sagittal alignment and lipomatosis .