Retrolisthesis, or backwards slippage of a vertebra, is an uncommon joint dysfunction. A vertebra is a small bony disc that makes the vertebrae, a series of small bones that form the backbone. Each vertebra is separated by a cushion of intervertebral discs, which are made of cartilage. Retrolisthesis occurs when a single vertebra slips and moves back along the intervertebral disc underneath or above it. There are three types of retrolistheses.
i. Complete Retrolisthesis
One vertebra moves backwards to both the spinal segments above and below.
ii. Partial Retrolisthesis
One vertebra moves backwards either to a spinal segment below or above.
iii. Stairstepped Retrolisthesis
One vertebra moves backwards to the body of a spinal segment located above, but ahead of the one below.
Retrolisthesis: What You Should Know, Health Line, https://www.healthline.com/health/retrolisthesis