4 week old chick suddenly can't stand her legs are shaking and curled in....help!

[Mk_lanch]

i have 2 chicks that hatched under one of my broody hens. they are both 4 weeks old (Almost 5 weeks)
this particular one is a poland x pekin bantam, she was completely fine with no problems 2 days ago...today i went to refill the water and i notice this chick almost in the splits position unable to walk properly. i immediately brought her home and have given her electrolytes . her legs are not broken her feet are curled in. her legs are shaking she cant put weight on them but can still move them and her toes.
does anyone know what this is? or how to treat it.

 

[50-45-1]

Has your chicks been eating chick starter?
This sounds like vitamin deficency.

 

[Mk_lanch]

its not a deficiency (ive been using this same very good chick starter for years) i believe its a break on the elbow. i have splinted and have her in a hammock so she doesnt put weight on it.
do you know how long i have to keep her in the hammock?