What would be the best approach to fix this butt indentation? (photos)

It's been over a year since fell down the stairs and my buttocks landed on a step. It was one of the most painful things I've experienced in my life. I had terrible bruising and swelling for weeks. I thought it would go back to normal but unfortunately it didn't. I tried lots of exercise, I weight 60lbs less than when the incident happen but the dent remains. I'm looking for something that won't require surgery or lots of downtime.