Spondylolisthesis refers to an abnormal slippage of one vertebral body on another. Instead of the vertebral bodies (main bones of the spinal column) stacking directly on top of one another, adjacent bodies "slip" on each other. This can be stable, meaning that it doesn't move when the back moves, or it can be unstable. An unstable spondylolisthesis can cause compression of the nerves in the spinal canal and significant low back pain.

Stable asymptomatic spondylolisthesis does not require treatment. However, unstable symptomatic cases are treated with a fusion. This generally involves decompression of the spinal canal and stabilization with screws and rods.