Emeraldgreen
I don't know if this will help but it sounds a bit similar, not so severe though. Our oldest furry child Heidi Ann is very arthritic and carries a big pouch on her belly, has a very hard time walking- it breaks my heart seeing how she struggles (she is on Metacam and Cosequin for this). Last winter we noticed when it was pedicure day that her nails l(mostly hae back ones) ooked exactly like what you described. I rushed her in to our vet and she said this is a yeast accumulation in the nail bed. It went away in a couple of weeks - not completely though, she still has it at the base of each nail. We watch her nails carefully because of this, and because she can't clean very well due to the pain in her joints, so there is always litter accumulating under the nail. I wonder if your baby's nail had a secondary infection from yeast? I hope your sweetie feels better soon.