I use shelf liner in the hatcher and over paper towels in the small brooder. I use paper towels over sand in the big brooder, then start reducing the paper towels as they get older. I tried shavings, but the dust was horrible and I find it hard to clean.
I read slipped tendons can be genetic, nutritional or from too high heat during incubation. I don't think it's nutritional, but could be either of the other 2. The poults with the leg problems came from someone else. They were her hen's first eggs. She had also set eggs, but lost them when her incubator quit. My last 2 hatched were from my hen and tom. I have 18 more (one pipped now), so we'll see if there's any more problems. If not, I might assume it's genetic. I did turn the heat down in the incubator for this hatch, but I think it might still be a bit high. Everything hatches early.