This radiograph shows you anterolisthesis at L4-L5. This didn’t reproduce very well but this is L4 and this is L5 and you can see that this one has slipped anteriorly relative to L5. This is a fairly large slip. Actually in some of the experiments, some of the work that we’ve done, this is basically what we measure, the extent of the slippage. When this happens, what this does is called encroachment upon the spinal canal making it narrower in this area so then you are more likely to get pinching of the spinal nerves.