I had some chicks hatch a while back that had wry neck. I dissolved part of a vitamin tablet in some warm water because I read it could be caused by vitamin deficiency. I figured I had nothing to lose, so I tried it and it worked. You could always try a vitamin solution in case the leg problem is due to that. It sounds more like it's an incubation problem, though. Perhaps if the humidity was too low the membrane inside of the egg began to contract as it dried and restricted movement. Unless it's my Jersey Giants, which tend to take an extra day to hatch, I don't keep the incubator running past the 22nd day. The longer something struggles to get out, the more likely there is to be either a) a deformity contributing to its untimely exit or b) injury as a result of being stuck so long. Is the foot drawn up and curled or is it open but they don't/can't put weight on it?