Spondylolisthesis is a condition in which a bone (vertebra) in the spine moves forward out of the proper position onto the bone below it.
In children, spondylolisthesis usually occurs between the fifth bone in the lower back (lumbar vertebra) and the first bone in the sacrum (pelvis) area. It is often due to a birth defect in that area of the spine or sudden injury (acute trauma).
In adults, the most common cause is abnormal wear on the cartilage and bones, such as arthritis.
Bone disease and fractures can also cause spondylolisthesis. Certain sport activities, such as gymnastics, weight lifting, and football, put a great deal of stress on the bones in the lower back. They also require that the athlete constantly overstretch (hyperextend) the spine. This can lead to a stress fracture on one or both sides of the vertebra. A stress fracture can cause a spinal bone to become weak and shift out of place.