The elastic white line is the link between the inner sensitive laminae and the insensitive outer hoof wall. Nothing would please me more than to write a helpful, informative article on white line disease for horse owners, but at this point, that article would have to be very, very short. We know very little about white line disease.
Many people have ideas about what it is and how to treat it, and some people are very successful.
I would suggest, however, that there is a great deal more to this whole problem than any of us know. First of all, on the humorous side, let's blame the Germans for writing their anatomy texts and research papers in German instead of English. Only now, as many as 20 years after several important papers were first written, are we obtaining translations of key studies of the structure of the hoof wall and analyses of hoof wall defects. Second, let's blame the entire state of Florida. In the 1980s, Americans started shipping horses to Florida to race, show, and be bred.