Pictures would be good to help see what is going on. The chick is a BO? Heavy bird, so only having one leg with its weight will be a strain on him. I had a pullet that the vet did amputate a leg on when it was about a week old due to slipped tendon, infected/broken joint at the hock. She led a very hard life. Because of the shift of her weight (she was an EE), her remaining hip joint would dislocate because of how she moved. She never could hop or walk, it was more of a flopping about. I had her euthanized when the quality of her life decreased.
I currently have one that had a slipped tendon that never went back in and the joint reversed, she uses it for balance but nothing else. She is doing very well, but is an INDOOR bird due to her handicap.
I would wonder, when you mentioned you had several with spraddle leg, about why? You shouldn't have many with spraddle leg unless there is something going on with the surface they are being kept on or something else happening during hatch. Good that those were fixable. With this guy/girl, I just don't know. Maybe others on here can add in.
