Spondylolisthesis occurs when a vertebra slides forward relative to the one below it, causing an abnormal alignment of the spine when viewed from the side. This misalignment can result from several causes, including trauma or degeneration. Spondylolisthesis can be congenital (present at birth) or develop in adolescence or adulthood. It can also result from physical stresses to the spine triggered by trauma, physical activity, or general wear and tear.