Medicare/MassHealth starting July - any way for a revision??

I had a gastric bypass in 2005i and have lost quite a bit of weight, but am still considered obese and am still having problems health-wise. I have a bad back from a car accident in late 2005, and am sure the weight doesn't help. I had a spinal fusion late 2009. I still have sleep apnea, depression, and have developed knee pain also. I want to know how difficult it may be to get a vertical sleeve gastrectomy if I've already had a gastric bypass. I have lost 140 lbs., but I need help losing more and I heard this may be a good surgery for that. I anticipate it may be much more difficult to try and get insurance to help me this time around, especially considering it will be Medicare and MassHealth. I'd think, however, if this can alleviate some of my medical problems, they may want to help me in order to save THEM money in the future. What do you think?