Just look at all the wasted muscles in alcoholics! Once they get off the alcohol,and improve nutrition and lifestyle they can go back to normal.

You obviously should be taking theraputic doses of Thiamin and other B vitamins like B12. Also Magnesium/calcium & D3 formulation.

You may need some PT and some strenghth training. It won't happen overnight, but it will happen. I also have a bad back, and understand the extra challenge involved.