Hi, we had a kit with this problem this spring,
The vet said it looked like either a calcium deficiancy or scoliosis... as our kits were supplimented with kibble mush as well as the raw rabbit from 3 weeks we think osteodystrophy unlikely and the rest of the litter were fine..
Hubby was gonna call it a day with this poor lil mite as he wasn't really getting around all that great at 8 weeks.. and we didn't want it to suffer a poor quality of life, like you, we didn't notice it until that time.. but within days he picked up a bit... ( we did add STRESS to the kibble for a couple weeks