Muscle atrophy in the butt - what are my options to fix this?

Allow me to answer your question as best i can without any photos. However, please keep in mind that an in-person, or at least a virtual, consultation with physical exam is first necessary before any legitimate evaluation or final surgical recommendations can be made.

There are currently only two FDA approved surgical options for augmenting the buttock/hip area: 1) Buttock and cosmetic Hip Implants (which are soft semi-solid silicone rubber implants that cannot rupture &/or leak) and 2)Brazilian Butt Lift (aka BBL) - which utilizes the patients own fat from liposuction then transfers this fat into the buttock. On the other hand, BBL using Sculptra is a dangerous, guaranteed waste of money, and is NOT FDA approved. So what it comes down to, like any surgery, is proper patient selection and long-term results. Implants provide the only guarantee for a sustained permanent result and tend to be ideal for perking up not only lean or deflated buttocks but also providing substantial projection to any butt, which is what every single patient wants.

Unfortunately, fat typically melts away leaving disappointing results after 12 months, often sooner. Unless your BBL surgeon is injecting only 200 to 300 ccs of fat into each buttock cheek, a large percentage of that fat is going to die. Dead fat leads to dents and dimpling like cellulite, unevenness, loss of projection, and fatty necrotic oil cysts which are hard marbles and can be very tender
Unfortunately, because ~70+ % of the fat transferred will melt away within a year, most patients are not good candidates for BBL because they lack an adequate amount of fat to harvest. Beware, if a surgeon asks you to purposely gain weight (i.e. fat) before BBL, know that the fat you lose first as you get back to your baseline weight after surgery is that very same fat that was transferred into your buttock, hence your new buttock shrinks first, the fastest, and the most...so please do not fall victim to this recommendation. Even those patients that had adequate amounts of fat pre-operatively, still end up seeking buttock implants after a year or so because most of the fat transferred melted away leaving them with minimal result. Fillers such as Sculptra are cost prohibitive, provided enough volume is injected (i.e. at least 400 cc of active ingredient costing over $300,000) and last only 12 - 18 months. So, if you're looking for a reliable, predictable, and long-term permanent option that also provides projection in the central buttock, buttock and hip implants are your solution. Please note that an extremely few number of board certified plastic surgeons specialize in buttock or hip implants, so you may need to travel far and away from home to find this particular surgeon. Glad to help.

It is difficult to discuss this issue without any photos and/or in-person evaluation. Very likely that injection of fat grafts could correct deformity to a certain degree. It is not likely that insurance would cover such a procedure. Good luck.

I know steroid injections can create fat atrophy but I’ve never heard of steroid injections creating muscle atrophy. Fat atrophy is a known risk of steroid injections this happens more frequently when injections are not injected deep into the gluteus muscle.
It’s a rare complication of steroid injections and unfortunate when it happens. Usually we wait to see if some other fat returns then consider fat grafting a.k.a. fat transfer as an option for volume restoration. Insurance is unlikely to cover this but you can contact your insurance company and see what they have to say.
Best,
Mats Hagstrom MD