so !
I've solve my fascia without the sliding attachement over my ribs, the solution was to have more volume on this area and put a very low value on volume conservation (0.01 in the poisson ratio)
I've also clean a little push on the knee when my leg is stretching. I've try to do this with volume conservation too, didn't works, then a I've put a sliding attachement but didn't work too, so I've clean it with a localised deltamush arround this area.
tell me if it look like ok and I lauch the rendering !!