Damaged bones or joints may cause vertebrae to move forward and shift the spinal column.
Degenerative Spondylolisthesis causes joints to weaken and vertebra to slip forward causing nerve roots to become pinched which then causes pain. This pain can radiate all the way to the legs and feet.
Isthmic Spondylolisthesis occurs when the vertebrae is fractured (broken) allowing the vertebrae to move forward. Pinched nerves will result and cause radiating pain to the legs and feet.