Joanie- It's called osteodystrphy. Here's a link to some info I found: http://www.guineapigwelfare.org.uk/satin-guinea-pigs/ ~Jaime, Mimi & Captain Phil the betta fish~ ~Missing Albert, Molly, Radar & Daisy~ http://s652.photobucket.com/albums/uu246/chirpy123/ http://www.etsy.com/shop/AintThatCrafty