Spinal fusion, also known as spondylosyndesis is a surgical technique used to combine two or more vertebrae. Supplementary bone tissue (either autograft or allograft) is used in conjunction with the body's natural osteoblastic processes. This procedure is used primarily to eliminate the pain caused by abnormal motion of the vertebrae by immobilizing the vertebrae themselves.

Reasons for spinal fusion

Spinal fusion is done most commonly in the lumbar region of the spine, but it is also used to treat cervical and thoracic problems. People rarely have problems with the thoracic spine because there is little normal motion in the thoracic spine. Patients requiring spinal fusion have either neurological deficits or severe pain which has not responded to conservative treatment.

Conditions requiring spinal fusion:

• degenerative disc disease
• spinal disc herniation
• discogenic pain
• spinal tumor
• vertebral fracture
• scoliosis
• kyphosis
• spondylolisthesis
• spondylosis
• Posterior Rami Syndrome
• other degenerative spinal conditions
• any condition that causes instability of the spine

Types of spinal fusion

There are two main types of lumbar spinal fusion, which may be used in conjunction with each other:

Posterolateral fusion places the bone graft between the transverse processes in the back of the spine. These vertebrae are then fixed in place with screws and/or wire through the pedicles of each vertebra attaching to a metal rod on each side of the vertebrae.

Interbody fusion places the bone graft between the vertebra in the area usually occupied by the intervertebral disc. In preparation for the spinal fusion, the disc is removed entirely. A device may be placed between the vertebra to maintain spine alignment and disc height. The intervertebral device may be made from either plastic or titanium. The fusion then occurs between the endplates of the vertebrae. Using both types of fusion is known as 360-degree fusion. Fusion rates are higher with interbody fusion. Two types of interbody fusion are:

• Anterior lumbar interbody fusion (ALIF)- an anterior abdominal incision is used to reach the lumbar spine
• Posterior lumbar interbody fusion (PLIF) - a posterior incision is used to reach the lumbar spine.

In most cases, the fusion is augmented by a process called fixation, meaning the placement of metallic screws (pedicle screws often made from titanium), rods or plates, or cages to stabilize the vertebra to facilitate bone fusion. The fusion process typically takes 6-12 months after surgery. During in this time external bracing (orthotics) may be required. External factors such as smoking, osteoporosis, certain medications, and heavy activity can prolong or even prevent the fusion process. If fusion does not occur, patients may require reoperation.

Some newer technologies are being introduced which avoid fusion and preserve spinal motion. Such procedures, such as artificial disc replacement, are being offered as alternatives to fusion, but have not yet been adopted on a widespread basis in the US. Their advantage over fusion has not been well established. Minimally invasive techniques have also been introduced to reduce complications and recovery time for lumbar spinal fusion.

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