What Causes Large Dent On The Thigh Muscle?

Several years ago, I was involved in a horse accident where a horse I was riding got spooked and in an effort to stop her, she rared up and fell backwards with me on her. I landed on the ground with my legs positioned as around the horse, with her on top of me. Then, she rolled over my right leg to get up. It seemed as though she was trying not to hurt me. When I was finally able to get up off of the ground, I immediately noticed there was a large dent (the dr called it a dimple) in my right thigh. Fortunately, there were no broken bones. It still looks exactly like that today. What is it that actually happened to the muscle and is there anything that can be done to repair/correct it? Thank you for your time and attention to my inquiry!