Spinal fusion is performed in following cases:

• Deformities of spine
• Scoliosis - A condition marked by a side-to-side curve of the backbone. The curve is usually shaped like an S or a C. In most cases, the cause of scoliosis is not known. In some cases, scoliosis may be present at birth or it may be caused by muscle spasms, inflammation, tumors, or certain other disorders. It may also occur at some point in time after radiation therapy to the backbone.
• Herniation and tumors of the intervertebral discs
• Spondylolisthesis - Spondylolisthesis is a spinal condition that causes lower back pain. It occurs when one of your vertebrae, the bones of your spine, slips out of place onto the vertebra below it. Most of the time, nonsurgical treatment can relieve your symptoms. If you have severe spondylolisthesis, surgery is successful in most cases.
• Spinal tumor A spinal tumor is a growth that develops within your spinal canal or within the bones of your spine. A spinal cord tumor, also called an intradural tumor, is a spinal tumor that that begins within the spinal cord or the covering of the spinal cord (dura).
• Stenosis - Spinal stenosis, a narrowing of the spaces in your spine, can compress your spinal cord and nerve roots exiting each vertebra. Age-related changes in your spine are a common cause. Symptoms include back and/or neck pain, and numbness, tingling and weakness in your arms and legs. Treatments are self-care remedies, physical therapy, medications, injections and surgery.