Spondylolisthesis is a condition in which one vertebra slips forward over the one below it. Spondylolisthesis is a fairly common cause of lower back pain and leg pain in younger adults (age 30 to 50), and degenerative spondylolisthesis is a fairly common cause of pain in older adults (age 50 and up). The most common symptoms are lower back pain and/or leg pain that limits activity level.