Vertebral Fusion Animation

Surgery for Spinal Instability

The vertebrae are the bones in the spinal column.  Fusion is a surgical procedure that joins two or more vertebrae together.  This short animation about vertebral fusion can help you understand why and how this spine surgery is performed.

First, though, it helps to know a little about the vertebrae and spinal regions.

Vertebrae and Spinal Regions


Number of Vertebrae


Cervical (neck)



Thoracic (upper back)



Lumbar (low back)

5 or 6

L1-L5 (or L6)

Sacrum (back of the pelvis)

5 bones fused together


Coccyx (tailbone)

4 bones


The cervical (neck) vertebrae are the smallest, and the lumbar (low back) vertebrae are the largest.  The thoracic vertebrae attach to the ribs and help make that region of the spine stable.

We have a spine expert-written article on this: learn more about the spinal column and vertebrae.

Spinal Instability: What Does That Mean?
The term spinal instabilitymeans abnormal motion between two vertebrae.  There are many spine disorders that may lead to spinal instability.  For example:

  • Degenerative disc disease may develop in the cervical spine.
  • Scoliosis is an abnormal sideward curve in the thoracic spine.
  • Lumbar spondylolisthesis occurs when one vertebral body slips forward over the one beneath it.

Those are just a few possible causes of spinal instability; your condition may not be listed, but your doctor should fully explain what’s causing your spinal instability.

Pain is a common symptom of spinal instability.  Sometimes the pain travels into an adjacent body part.  For example, a problem causing neck pain (eg, herniated disc) may cause tingling, weakness, or pain in an arm or hand—that’s cervical radiculopathy.

Similarly, a disorder such as spondylolisthesis can cause low back and leg pain—the leg pain is lumbar radiculopathy (although you may hear it referred to as sciatica).

Fusion Stabilizes the Spine
The purpose of fusion is to stop abnormal motion of two (or more) vertebrae.  Fusion is often combined with another surgical procedure called decompression.  Decompression is performed to surgically remove bone or tissue pressing on the spinal nerves; this nerve compression can cause pain, so by removing whatever is pressing on the nerve, the goal is to lessen the pain.

Spinal Fusion Surgery Example

  • A disc herniates at C4-C5, compresses an adjacent nerve root, and causes spinal instability and pain.  The surgeon performs a discectomy through the front of the patient’s neck and removes the damaged disc, which takes the pressure off nearby spinal nerve roots.
  • Bone graft is used to fill the empty space between C4 and C5.  The surgeon can obtain bone graft by harvesting small pieces of bone from the patient’s hip (this type of bone graft is called autograft).  Or the surgeon may use bone graft that doesn’t come from your body; that’s called allograft.
  • The bony pieces are packed into the empty disc space.  A metal plate covers the front of the C4 and C5 disc space, and is secured in place using bone screws.  The metal plate holds the bone graft in place and helps stabilize the spine while it heals.  
  • The bone graft stimulates new bone to grow, which eventually fills the empty space and fuses C4 and C5 together. 

Depending on the extent of the surgery, your overall health, and other factors, you may have to wear a brace after surgery.  The brace provides additional support while the spine heals.

After Vertebral Fusion:  Spine Surgery Recovery
Several times during the first year after surgery, you will have follow up appointments with the surgeon.  Periodically, x-rays are taken to monitor the progress of the vertebral fusion and make sure the bones are healing correctly.

Updated on: 03/22/16