what is grade 1 anterolisthesis of l5 on s1?
Anterolisthesis is a spine condition in which the upper vertebral body, the drum-shaped area in front of each vertebrae, slips forward onto the vertebra below. The amount of slippage is graded on a scale from 1 to 4. Grade 1 is mild (less than 25% slippage), while grade 4 is severe (greater than 75% slippage).