Edit: Beaten to it by Daybreaker.
Fuzzie mice for a ball python?Yeah, that is far too small of a meal even for 95% hatchlings. Most can easily eat rat fuzzies right out of the egg, which are several times the size of fuzzy mice.
Although I'm sure his back injury could have played a part in his stunted growth, from the facts that have been presented I believe that the main reason he isn't growing is because of not being fed properly. I would bump up his prey size (15% of his body weight every 5-7 days is adequate).
Under/over feeding is a common mistake amongst new owners. I wish more would take the time to ask questions like you have. Good luck!