Spondylolisthesis describes a condition of forward slippage of one vertebrae in the spine over another. This condition in adults is most commonly due to degeneration (wear and tear) of the discs and ligaments that bind and support the spine. With aging, discs lose water content and ultimately height. As the vertebra on either side of the disc come closer to each other through the loss of disc height, the upper vertebra slides forward on the sub adjacent vertebra producing spondylolisthesis.