Osteophytes grow, because usually it is your body feeling that the spine, or that area of your body is not supported sufficiently at that point.
After ADR, obviously some of the bone tissue has been taken away because they scrape the flat surfaces of the vertebrae, where they implant is going to be until it bleeds. Hence you have got to think your body suddenly shouts "hello" what is going on here, and decides to grow some more bone to support what has been going on.
Unfortunately bodies don't have 50-50 vision, and we sometimes get osteophytes in the wrong place. They can be dealt with and special cement put over where they had been removed so they don't re grow. This is a very simplistic explanation and I have got a huge article about it from Medscape but I don't think it would fit on a page here.
Best,
Alastair
