Anterolisthesis

Forward sliding of one vertebra on the one below it: Grade I – 1-25% Grade II – 25 – 50% Grade III – 50 – 75% Grade IV – 75 -100% The vast majority are Grade I, but even that can be significant if there is also a bulging disc, arthritis, or other factors that narrow the central spinal canal or the narrow neuroforamina through which nerve roots pass on their way to the legs or arms.