Spondylolisthesis Reduction: these are the steps to realign a spine that has shifted forward due to a pars fracture in the back of the bone. The white circles show where the bones have broken allowing the strain of the body and activity to be absorbed by the disk. Over time, this results in failure of the disk and an anterior slippage of the spine that progresses, causing back and leg pain. It also has an impact on the disks above and below which begin to shift as well and may become unstable.
Some doctors leave the slip in place and fuse the spine without realigning it. The problem is, the spine and its normal state are in a perfectly balanced position. Even with a stable spine that is translated forward, the muscles are forced to battle the effects of gravity in an abnormal position, which commonly leads to increased back pain and muscle fatigue. My preference is to remove the disk and systematically realign the disk by not only improving the height of the disk but also the curvature in the position of the bone which has slipped forward.
As you see in these pictures, Step One involves removing the disk from the front to reestablish the height of the disk and simultaneously improve the position of the spine. You can see from the red arrows that the spine slips back closer to the normal position even with just the removal of the disk and placement of the bone graft between the bones that are slipped forward. Once the disk has been replaced by bone graft, screws or then placed in the back of the spine over the levels to be fused. The bone, which is forward, has a special screw with an extended head that allows the surgeon to place a rod above and below the shifted bone while still capturing the screw. When the rod is placed within the heads of the screw and the set screw is tightened the bone that is slipped forward slowly pulls back into place.
The surgeon must be careful that the nerve is not injured in the process. For that reason, my preference is to remove the disk in the front first to improve the height, followed by removal of the broken bone in the back and removal of all the scar and bony fragments compressing the nerve in the back prior to realigning the spine. This prevents the nerve from being damaged in the process of realignment. Once the spine is realigned and the rods are in place and final tightened, bone graft is placed along the side of the spine, in addition to the bone in the front, to ensure the bones fuse together over time. ~Dr Cyr