Fusion is the process of joining bones with bone grafts, adding bone graft or bone graft substitute to an area of the spine to set up a biological response that causes the bone to grow between the two vertebral elements and thereby stop the motion at that segment. The fusion process essentially "tricks" the body into thinking it has a fracture.

Posterior cervical fusion is a procedure that is performed on the low back region for reasons such as instability of the spine, fracture, degenerative disc disease, or stabilization for tumors. The goal with fusion is to stabilize the spine so that pain or deformity is reduced.

The General Procedure:

1. Surgical approach
• The surgical approach to the spine is from the back through a midline incision.
• The muscles are dissected off of the lamina, and the facet joints and lateral mass are identified.
  
  
2. Preparation of the fusion bed
• The soft tissue and cartilage of the facet joints are then removed.
• The surfaces are meticulously prepared for bone graft by burring or with a gouge. This allows surface area for the ingrowth of bone.


3. Bone graft and fusion
• Bone graft is often obtained from the pelvis (the iliac crest).
• Alternatively, bone graft substitutes and extenders can be used.
• Next, the bone graft material is laid out in the posterolateral portion of the spine, and packed into the facet joints.
• The back muscles are then released over the bone graft, creating tension to hold the bone graft in place.

In a posterolateral gutter fusion, the surgical approach to the spine is from the back through a midline incision that is approximately three inches to six inches long. The muscles are dissected off of the lamina, and the facet joints are identified. The soft tissue and cartilage of the facet joints are then removed, preparing the surfaces for bone graft. A small extension of the vertebral body in this area (transverse process) is a bone that serves as a muscle attachment site. The large back muscles that attach to the transverse processes are elevated up to create a bed to lay the bone graft on. The soft tissue and cartilage of the facet joints are then removed, preparing the surfaces for bone graft.

Bone graft is often obtained from the pelvis (the iliac crest). Most surgeons work through the same incision to obtain the bone graft and to perform the spinal fusion. Alternatively, bone graft substitutes and extenders can be used. Next, the bone graft material is laid out in the posterolateral portion of the spine, and packed into the facet joints. The back muscles are then released over the bone graft, creating tension to hold the bone graft in place.

The body responds by building bone between the moving segments to stop them from moving. Standard posterior fusion is achieved between the facets and the transverse process of adjacent vertebrae. Instrumentation may be added to hold the vertebrae together to help increase the chance of fusion.

The success rate for posterior fusion in the treatment of refractory discogenic back pain is only 60-70%. The success rate is higher when there is frank instability due to fracture or to spondylolisthesis.

The selection of the appropriate patient for this surgery has been blamed for the relatively poor results when fusion is used for treatment of discogenic back pain. Other possible causes of poor results are that the actual pain-causer, the disc, is not addressed. See discussion of PLIF - Posterior Lumbar Interbody Fusion.

However, a solid fusion is not always achieved. There are a few factors that patients can control that are important in determining whether or not a fusion grows in solidly, including:

• Smoking cessation. It is generally advisable to quit smoking prior to a spinal fusion procedure, as nicotine is a direct toxin to bone graft and will prevent the bone from forming.
• Limited motion. Bone forms better if motion is limited, so patients are often advised to avoid bending, lifting, and twisting for up to three months after spinal fusion surgery depending on the amount of instability.