What it means
Each vertebra normally sits squarely on the one below. In spondylolisthesis, one has shifted, usually forward (anterolisthesis) and sometimes backward (retrolisthesis). In older adults it most often comes from worn discs and facet joints, typically at L4-L5. In younger people it often follows a pars defect (spondylolysis). Grade 1 means it has moved less than a quarter of the way across the bone below. Grades 2 to 4 mean more, and a complete slip is sometimes called grade 5.
When it matters
Most slips seen on scans are low grade, and many cause no symptoms. Doctors look more closely when the slip narrows the spinal canal or nerve openings, or when it might move with bending (instability). X-rays taken while bending forward and back can check for movement, and older images show whether the slip has changed. Higher grades, or leg pain and weakness, often lead to a spine specialist review.
Questions to ask your doctor
- What grade is the slip, and is it from wear or from a pars defect?
- Does the slip narrow the spinal canal or the nerve openings?
- Would X-rays taken while bending show whether the slip moves?
