One out of 500 chicks arrived spraddle-legged, so I don't believe that IN MY CASE it was a vitamin deficiency.  I tried many different things to tape up the legs, bind them together, etc., but all failed.
This little chick has such a will to survive, that I've placed her in a very small group (15) so she doesn't have a lot of competition for food.  She's much smaller than her fellows, but is healthy and vigorous.  
I just didn't have the heart to euthanize a vigorous little chick who was born with a deformity.  None of the other chicks peck at her not working leg (which is now stretched out behind).  I know she'll never be a productive member of her flock - but I feel that I can "carry" a handicapped little pullet.  
I've really agonized about this, but feel that as she was born this way, this is all she knows, and I simply cannot kill her just because she's "different".  She seems perfectly content.
AFTER it was too late, I came across something on the internet that showed "chicken in a box" as a cure for spraddle-leggedness.  It's too late for me to know if this would have worked, but I really did try really, really hard.  
Can slipped tendons be cured the same way?