The treatment of spinal disorders is complex and must be individualized to each patient’s unique circumstances. In simple terms, the purpose of fusion surgery is to realign a spinal deformity and/or stabilize a segment of the spine to prevent painful motion (or micro-motion). The most common reasons for performing fusion surgery are:

• Spondylolisthesis
• Degenerative scoliosis with lateral listhesis
• 1 or 2-level painful degenerative disc disease

Fusion Surgery for Spondylolisthesis
Spondylolisthesis is a forward slippage of one vertebral body (outlined in square boxes) over the vertebra beneath it (arrows).
Spondylolisthesis occurs in both younger and older patients, and causes pain in the low back (lumbar spine) to radiate downward in the legs. Fusion surgery is limited to the area that is malaligned—usually at a single level, as shown in the above images.

Spine surgeons may use implants to hold the spine in the proper position while the bones heal together (called fusion, bones fuse). Most commonly, screws are placed (implanted) into the bones and interconnected using rods. A cage (or interbody device) may be implanted between two vertebral bodies to increase the amount of space between the two vertebral bodies (see image below).

Fusion Surgery for Degenerative Scoliosis with Lateral Listhesis
In a patient with degenerative scoliosis with lateral listhesis, the purpose of fusion surgery is to realign (straighten) a part of the spine while simultaneously decompressing the nerves. The abnormal curvature of the spine (degenerative scoliosis) and slippage (lateral listhesis) can also cause spinal stenosis (narrowing of the space for the nerves). The key finding, besides the degenerative scoliosis, is a sideways slippage called lateral listhesis (see arrow).

The typical patient is 60-70 years of age and has low back pain, difficulty standing, and achiness in the legs/calves when standing and walking. Most patients cannot walk more than 1-2 blocks. Surgery usually requires fusion at each level of deformity (ie, degenerative scoliosis). Deformity is the most common reason why a spine surgeon recommends multilevel spinal fusion.

Fusion Surgery for Painful Degenerative Disc Disease
Degenerative disc disease, which is often painful, often responds to nonoperative treatments, such as nonsteroidal anti-inflammatory drugs (NSAIDs), spinal injection therapies, and organized physical therapy. Most patients report their low back pain is aggravated by normal daily activities.

Fusion surgery may be recommended if a comprehensive nonoperative treatment program has been pursued for at least 6 months, and despite the effort, the patient continues to experience severe pain that greatly limits their function and quality of life.

Conclusion
As stated at the outset of this article, the decision-making process for fusion surgery is complex and should be made on an individual basis. The three examples shown represent the most common diagnoses and circumstances under which fusion surgery may be recommended. Other spinal disorders that may necessitate fusion surgery include infection, tumor, trauma, and/or a previous failed spinal surgery.

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