Wear and tear of the discs and facet joints above and below a level that has been fused has haunted many people after fusion surgery. This in part is due to increased motion and shearing forces at these levels because the fused level has lost some of its mobility. There is now a published study that shows that in human subjects, disc replacement allows motion at the segment that is operated on that is very similar to people who have not had surgery. Theoretically, this should eliminate problems with wear and tear above and below the segment where the disc has been replaced. This appears to be the greatest advantage of disc replacement vs. lumbar fusion.