Anterolisthesis: The forward positioning of one spinal vertebra in relation to the adjacent vertebra beneath it. Anterolisthesis can be graded: Grade 1 is less than 25% slippage, grade 2 between 25%-50% slippage, grade 3 between 50%-75% slippage, and grade 4 greater than 75% slippage. Symptoms of anterolisthesis depend on the severity, location, and cause. The opposite of anterolisthesis is retrolisthesis or backward positioning of one vertebra in relation to the adjacent vertebra beneath it.
Klippel, J.H., et al. Primer on the Rheumatic Diseases. New York: Springer, 2008.