Debbie
I don't know anything about your previous CRPS experience so i apologise if anything I post is irrelevant to you but I hope it's some help.

When you say that athletes use steroids and so you are considering them for atrophy, I don't know if you are meaning athletes using steroids legally or illegally. There are countless different types of steroid which have different effects. Illegal use involves intramuscular self-injection of steroids but it is completely useless without also doing significant physical training. The steroids themselves do nothing useful, its only when an athlete then trains that any benefits (over and above training without use of steroids) may be obtained. It allows athletes to recover faster, train longer and harder or develop greater muscle and bone mass than would otherwise be obtainable.

If you are talking about legal steroid use in athletes, this is very heavily controlled and regulated. Steroids are prohibited by all sports that subscribe to the world anti-doping provisions and any exceptions have to be medically justified in advance of administration (except in emergencies when approval must be obtained retrospectively). The kind of purpose for which you are considering steroids is very unlikely to be relevant to anyone who is an athlete operating legally.

Steroids have been used to treat people with HIV and MS who have muscle atrophy but the success depends on the reason for the atrophy occurring in the first place. It's not helpful with disuse atrophy and where neurogenic (nerve related) atrophy exists, it seems to depend very much on the exact type of underlying neurogenic atrophy at work. There is also some evidence that exercise is just as effective in many neurogenic atrophies.

I am guessing from your posts you dont yet have a known cause for your atrophy. It's possible that your atrophy is disuse related but the amount of exercise you are able to do in the pool just isn't enough to stop the atrophy, let alone to reverse it. It may be a neurogenic form but usually this can be determined because the two types don't present in the same way. Its always worth discussing the options with your doctor to see if steroids will help but the seriousness of the side effects can't be ignored and many of the causes of muscle atrophy, unfortunately, won't respond so the odds might be against you.