Sorry, just saw this. From what I can see, I would suspect maybe a bone deformity as well. Maybe from being malpositioned in the egg. I've seen distorted keel bone in a couple of chicks hatched here that were malpositioned and had to be assisted at hatch. If vet care is an option, then an xray might show something. If not, and the bird is doing well, getting along in the flock, then I probably wouldn't worry, just let it be unless it's causing problems. I probably wouldn't hatch eggs from that bird, assuming all else is normal and it's able to lay.