Get a good physical therapist. Maybe if you exercise a lot, but a lot.

I had atrophied upper legs (thinner than my calves and they are thin). It took more than a year of 1000 leg lifts a day per leg (with a rolled towel underneath my legs, lifting my heel off the bed - basically with locked kneecaps). But I regained most of it. It is do-able and was almost insane in my case, provided you get the best care and you put your shoulders under it.