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In some conditions, due to the severe deformation and loading of the spine, one of the vertebrae may slip forward, backward, or to the side. These deformities that can occur in addition to adult degenerative scoliosis are named spondylolisthesis when displacement is to the front, retrolisthesis when displacement is to the back, and listhesis when displacement is to the side. These movements may result in pain, they may also cause leg pain or muscle weakness due to compression of the nerve and/or spinal cord.