Spondylolisthesis by its nature causes instability of the spine. This instability has an adverse effect on the disc immediately below the displaced vertebra and can influence the development of degenerative changes to a moderate to severe degree.
Spondylolisthesis has been classified into grades I, II, III, IV and V depending on the severity of the displacement of the vertebra above on the vertebra below. In severe cases involving the lumbar spine, cauda equina syndrome can occur.
Spondylolysis & Spondylolisthesis - USC Spine Center
Spondylolysis and Spondylolisthesis usually cause no symptoms in children; however, many seek medical evaluation because of a postural deformity or gait abnormality. Pain most often occurs during the adolescent growth spurt and is predominantly backache, with only occasional leg pain. Symptoms are exacerbated by high activity levels or competitive sports and are diminished by activity restriction and rest. The back pain probably results from instability of the affected segment, and the leg pain is usually related to irritation of the L5 nerve root.