In adults, scoliosis may result from degeneration of the spine in old age that leads to the deformity. The area of the vertebra called the pedicle is affected. The pedicle is part of the bony ring that protects the spinal nerves. The pedicle also connects the vertebral body to the facet joints. When a spondylolysis is present, the back part of the vertebra and the facet joints simply are not connected to the body - except by soft tissue.
Spondylolisthesis is the term used to describe when one vertebra slips forward on the one below it.
This usually occurs because there is a spondylolysis in the vertebra on top. There are two main parts of the spine that keep the vertebrae aligned - the disc and the facet joints. When a spondylolysis occurs, the facet joint can no longer hold the vertebra back. The intervertebral disc may slowly stretch under the increased stress and allow the upper vertebra to slide forward. In the past, spinal fusions of the lumbar spine were performed without any internal fixation.