Injections of esterone will not really help. THe esterone can help build muscle more over the hips of the horse, versus along the stifle (patella-ACL muscle). It will help develop the upper hip, not the lower where most stifle problems occur. Have your vet xray for chips. If nothing is torn (ACL or bone chips) you can inject the joint and it will tighten internally the ACL. BUT and please keep this in mind..nothing works permanently!!! If the horse takes a bad step and slips, they can re-tear or injure the stifle. I've had the stifles injected on one horse and he had to be done every year (dangers include infection ect) so he went to a pasture pal. THe other horse I only had done once and he has actually "dry" in his hock joint..never did him again. Only under extremely hopefully cases will I inject joints, I prefer to use methods of strengthening to help problems.
AND age can have a factor..give the colts time to grow. As for pain meds, my vet actually told me to let him be a little sore, the horse was less inclined to rip and snort during the healing process and that the inflammation (along with continued EASY straight line work) would help strengthen. He wanted the horse literally sore in BOTH stifles versus the just the bad one, so when he injected and horse went back to walking miles in straight lines he would keep even steps with two sore legs versus just the left or right. Unless the horse is shocky or can't put any weight on a leg, I will cold/hot hose and leave alone. There is a reason when we hurt ourselves we tend to take it easy and favour