Spondylolisthesis refers to the phenomenon where one bone of the spine (vertebral body) has slipped over another vertebral body. This can imply a certain degree of instability of the spine. There are different types of spondylolisthesis. They can be congenital or develop later in life from processes such as degeneration (degenerative spondylolisthesis) or from an injury (spondylolytic spondylolisthesis). Spondylolisthesis can cause back pain and sometimes result in compression or pinching of the nerves. This can result in pain, numbness or tingling in the legs. A medical consult should be made if there are such symptoms.