Spondylolisthesis is a condition in which one bone in your back (vertebra) slides forward over the bone below it. In some cases, this may lead to your spinal cord or nerve roots being squeezed, causing back pain and numbness or weakness in one or both legs. Sometimes when a vertebra slips out of place, you may have no symptoms at all or no symptoms until years later. Your chiropractor or physician can tell you more about this condition and how to manage it.