Hi. My 12 Year Old Son Sprained His Knee Pretty

Hi. My 12 year old son sprained his knee pretty bad before Thanksgiving. The ortho dr took xrays and there was no tear or break. Said sprained the ligament that attaches to the top of shin bone. Just put him in a knee immobilizer brace fore about a week. It's getting better, but very slowly. He is complaining that his hip hurts (I think it is from trying not to hurt his knee). He also has trouble making his bad knee/leg turn toward the front .(says it hurts his hip to turn it ) Any suggestions? His Dr. didn't even give us any exercises to do. It hasn't helped that he has to go up and down stairs on his crutches at school.