Lumbar Spinal Fusion

Spinal fusion is a surgical procedure used to correct problems with the small bones in the spine (vertebrae). The basic concept is to fuse together two or more vertebrae so that they heal into a single, solid bone. This is done to eliminate painful motion and/or to restore stability to the spine.

Spine surgery is usually recommended only when there has been a failure of non-surgical (conservative) management, and there is a clear source of pain. Imaging tests, such as x-rays, computerized tomography (CT) scans, and magnetic resonance imaging (MRI) scans along with diagnostic injections may be needed for confirmation of the diagnosis prior to considering fusion surgery.

Spinal fusion may help relieve symptoms of many back problems, including:

• Degenerative disc disease
• Spondylolisthesis (slippage of one vertebra on another)
• Spinal stenosis (narrowing of the spinal canal)
• Scoliosis (curvature of the spine)
• Fractured vertebra
• Infection
• Herniated disc or recurrent disc following previous surgery
• Tumour involvement of the spine.

Description

Spinal fusion eliminates motion between vertebrae. It also prevents the stretching of nerves and surrounding ligaments and muscles. It is an option when motion is the source of pain, such as movement that occurs in a part of the spine that is arthritic or unstable due to injury, disease, or the normal aging process. The theory is if the painful vertebrae do not move, they should not hurt.

A decompression (laminectomy) is often also performed at the same time, especially if there is leg pain or arm pain. This procedure involves removing bone and diseased tissues that are putting pressure on spinal nerves.

Fusion will take away some spinal flexibility, but most spinal fusions involve only small segments of the spine and do not limit motion very much. The majority of patients will not notice a major decrease in range of motion.

Procedure

Lumbar and cervical spinal fusion have been performed for decades, and there are several different techniques that may be used to fuse the spine. There are also different "approaches" that may be utilised:

• Approaching the spine from the front is called an anterior approach.  It requires an incision in the lower abdomen for a lumbar fusion or in the front of the neck for a cervical fusion. 
• A posterior approach is done from the back. 

    orthoinfo.aaos.org

Illustration of a posterolateral lumbar fusion (PLF) shows bone graft material placed over and between the transverse processes of the vertebrae. Screws have been placed ready to join to rods to provide stability to the spine while the fusion heals. 

• A lateral approach approaches your spine from the side. 
• Minimally invasive techniques have also been developed, and these may allow fusions to be performed with smaller incisions, but ultimately the right procedure for you will depend on the nature and location of your disease.

Bone Grafting

All spinal fusions use some type of bone material, called a bone graft, to help promote the fusion. Generally, small pieces of bone are placed into the spaces between the vertebrae to be fused. A bone graft is primarily used to stimulate bone healing. It increases bone production and helps the vertebrae join together into a solid bone. 

Previously, a bone graft harvested from the patient's pelvis was the only option for increasing the material needed for fusing the vertebrae. This type of graft is called an autograft. Harvesting a bone graft requires an additional incision during the operation. It lengthens surgery and can cause increased pain after the operation.

If you are having a decompression procedure at the same time, bone may be harvested from the site of the decompression and used as the graft. This type of graft is called a local autograft. The bone is essentially recycled - it is moved from where it is compressing your nerves to the area the surgeon wants to fuse.  

An alternative to harvesting a bone graft is an allograft, which is cadaver bone, typically acquired through a bone bank.

Several artificial bone graft materials have also been developed:

• Demineralized bone matrices (DBMs) - Calcium is removed from cadaver bone to create DBMs. Without the mineral, the bone can be changed into a putty or gel-like consistency. DBMs are usually combined with other grafts, and may contain proteins that help in bone healing.
• Bone morphogenetic proteins (BMPs) - These very powerful synthetic bone-forming proteins promote a solid fusion. Autografts may not be needed when BMPs are used, and they can be easily added to synthetic grafts.
• Synthetic bone - These are made from calcium/phosphate materials and are often called “ceramics.” They are similar in shape and consistency to autograft bone. Newer technology synthetics can add special coatings to drive the healing towards bone (by addition of Silica, or by using nanotechnology).

Immobilization

After bone grafting, the vertebrae need to be held together to help the fusion progress. This may be achieved with the support of a special brace.

Plates, screws, and rods (called internal fixation) increase the rate of successful healing. With the added stability from internal fixation, most patients are able to move earlier after surgery.

  orthoinfo.aaos.org

In this x-ray of a posterolateral lumbar fusion (PLF), a rod and screws have been used to prevent motion at the spinal segments being fused.

Complications

As with any surgery, there are risks associated with spinal fusion. Risks will be fully discussed with you before your procedure, and specific measures will be used to help avoid potential complications. Potential risks and complication of spinal fusion include:

• Infection - Antibiotics are regularly given to the patient before, during, and often after surgery to lessen the risk of infections. The current rate of infection following lumbar fusion is 2.2%.
• Bleeding - A certain amount of bleeding is expected, but this is not typically significant, and transfusion is usually not required.
• Pain at graft site - A small percentage of patients will experience persistent pain at the bone graft donor site (if this is done).
• Recurrent symptoms - Some patients may experience a recurrence of their original symptoms, and there are multiple potential causes for this. 
• Pseudarthrosis - This is a condition in which there is not enough bone formation. Patients who smoke are more likely to develop a pseudarthrosis. Other causes include diabetes, older age, and moving too soon (before the bone has fused). If this occurs, a second surgery may be needed in order to obtain a solid fusion.
• Nerve damage - It is possible that nerves or blood vessels may be injured during these operations. These complications are very rare.
• Blood clots - Another uncommon complication is the formation of blood clots in the legs. These pose significant danger if they break off and travel to the lungs.
• Adjacent segment (junctional) failure – This occurs typically years later due to forces being transferred to the levels above or below the fusion segment.

Recovery

Pain Management

After surgery, you will feel some pain, which is a natural part of the healing process. Medications are often prescribed for short-term pain relief after surgery. Many types of medicines are available to help manage pain, including Paracetamol, opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), and local anaesthetics.

Rehabilitation

The fusion process takes time, and it may be several months before the bone is solid, although your comfort level will often improve much faster. During this healing time, the fused spine must be kept in proper alignment. You will be taught how to move properly, reposition, sit, stand, and walk. Your symptoms will gradually improve, as will your activity level.

Directly after your operation, only light activity is recommended, like walking. As you regain strength, you will be able to slowly increase your activity level. Physical therapy is typically started from 6 weeks to 3 months after surgery, though hydrotherapy may be used much earlier.