Injured Chick- Infection????- Leg problem!

Help! This little baby has been having issues since he hatched, with the first week and a half of his existence being spent giving him Nutri-Drench daily with a syringe until he started eating and drinking properly on his own. I thought he was on his way to a full recovery, when I noticed this issue this morning! His left ankle joint is twice the size of the other! He can still use his leg and bend it from what I can see, but he holds it at a funny angle. It's hard when I gentle squeeze it, not squishy. Is this just a sprain? Will keeping him separate of the others for a while help this? is there anything else I can do? I don't want to lose this little guy!

Added: I've put him by himself in a ten gallon fish tank inside the large brooder, part of it under the light and part of it not. I've got a metal mesh lid on top to keep the other chicks out. He's got his own nutri-drench fortified water and his own food. He doesn't seem too upset by the fact that he can't get out, as long as the other chicks are milling around the other side of the glass.

So, the little one's leg isn't getting any better and he's been looking miserable inside the fish tank. I let him out into the expanded brooder with the rest of the chicks and he did a super excited run/hop while flapping his wings all over the place. Obviously, he feels well enough to do that, but his leg is causing him trouble.

I am noticing some squishy whitish-yellow pockets all around the swollen area and I'm afraid it's an infection. What can I do or give him to clear it up?? Thanks!

I probably also put this thread in the wrong place... I'll put it in the injuries forum. Bleh.