I injured my back in a car accident 5 years ago and spun my L3-5. So i know exactly what you are going through. Continue to do sumo deads and front squats since those really hit your quads. Also to start rehabing your back do light weight high reps and stretch in between sets. And slowely work back into back squats once your back is healed. That's what I did mostly for my lower back and overall it feels pretty good.