Low back pain sometimes comes from instability of the spine. This instability is manifested in the imaging tests for abnormal movements in X-rays performed in movement or misalignments of the spine (the so-called spondylolisthesis) and is characterized by being a pain of a mechanical type, that is, related to certain postures and exercises and that improves with repose. Occasionally the nerve roots may also be compressed, which causes lower back pain to add pain in the legs.