You should be seeing improvement by now... chicks grow very quickly and joint issues can quickly become crippling if they don't heal in time to keep up with their growth. Can you give us a full update of eating\drinking, activity level compared to the rest of the hatch - ability to move around or put weight on the legs? It may be that this chick is failing to thrive and there are so many things that can factor into a poor chick like genetic defects, parent nutrition, health and age, incubator conditions etc... what was your hatch rate for this batch? Did you have any late quitters?