We adopted a bantam Silver Spangled Hamburg hen last fall. She had a pronounced limp and (what I now know to be) the telltale crusties on her legs. At the time, I wasn't sure what was going on or what to do. This spring I did sort of figure things out and started treating her legs with VetRX. We saw some improvement but there was so much crud built-up, she was still limping.
After finding this thread, I brought her into the house and soaked her feet for ~30 mins. That softened the crud and I was able to use a combination of tweezers, a cuticle removing tool and a paring knife to get most of build-up off. Her toenails were quite long and hooked, so I cut them back as I would my dogs. She has light nails so you can still see live cuticle bed. One of her outside toes lost the nail completely.
I have her confined in a cat carrier with some snacks and water while her leg feathers dry. I've also treated her legs with antibiotic ointment in hopes that the rest of the crud with slough off this afternoon.
A great big thank you to froggiesheins for the doctoring advice. I sort knew what to do but it helps immensely to read someone else's experience.