We're having the very same issue with a 6-day old chick, too! Anyone with any advice, please reply.
A silver-laced wyandotte chick, she's the same age as 3 other very perky brooder-mates, and already noticeably smaller. She still eats and drinks when given the chance (I've been spoon-watering her a couple times a day), and her legs/joints look no different from each other, in terms of swelling, shape, color, etc. Have read so much about slipped tendons, splay-leg, vitamin B deficiency as it relates to toe and leg problems, but nothing we've tried, from vitamins, egg protein, gently moving the joint, - has seemed to help her/gotten any better over the last 24 hours.
Her left foot now seems limp/unresponsive, and she's been using her wings to try to keep balanced, even though she's hunkering down low and doesn't try to stand often if at all.
We really don't want to lose her, and we're very new at this! Any ideas as to the problem?