A spinal fusion is a surgical procedure that joins spinal segments together to eliminate motion at that segment, with the goal of decreasing pain.
The gold standard of spinal fusions is the posterolateral gutter fusion.
Posterolateral gutter fusion is done in the lower back to relieve pain that is occurring as a result of lumbar degeneration.
This image shows the segments where a posterolateral gutter fusion is done: L1 - L2 through L5 S1 at the bottom of the spine. The most common segments to need a fusion are at L4 - L5 or L5 - S1.
To stop the motion at the affected segment, a bone graft will be placed along the posterolateral portion of your back, shown here in purple.
First your surgeon will make a 3-6 inch long incision in the midline of your back, and retract the muscles surrounding the spine. In this image, the muscles are shown in purple, and you can see the exposed spine.
At this time, your surgeon may perform a laminectomy to remove any excessive bone that is putting pressure on your nerves.
Next, your surgeon will retrieve bone for the graft from the iliac crest. The iliac crest is the uppermost part of the back of the pelvis. Your surgeon may be able to retrieve the bone graft through the original incision on the midline of your back. Read Autograft: The Patient's Own Bone for more in-depth information.
In some cases, synthetic or cadaver bone graft may also be used.
Once your surgeon has the bone graft ready, he or she will expose the posterolateral area of your back by removing the muscles that attach to the transverse processes.
This area has a high concentration of blood vessels, which is crucial for helping the body generate the new tissue for the bone graft. Your surgeon will then place the bone graft morsels (shown here as reddish cells).
The muscles are then placed back down over the graft. They will hold the graft in place as your body heals.
The same process is repeated on the other side of the spine, so that both sides will fuse.
In some cases, your surgeon may use pedicle screws and rods in addition to the graft to provide additional stability while the bone is fusing.
This image shows the result of the fusion after several months of healing: The body's natural healing responses have helped the bone graft and adjacent vertebral bodies fuse into a single bone.
A successful fusion surgery depends on several factors, including a correct diagnosis, the skill of your surgeon, and having a reasonably healthy lifestyle.
For a full discussion on recovering from your fusion surgery, start with this article: Spinal Fusion Surgery Recovery: After Discharge (Three to Six Days).