Introduction

One of the main goals of any surgical procedure on the skeletal system is to stop the pain caused by joints that have worn out over time–degenerative joints. One of the most reliable ways to reduce pain from degeneration is to fuse the joint together. A fusion is an operation where two bones, usually separated by a joint, are allowed to grow together into one bone. The medical term for this type of fusion procedure is arthrodesis.

Description

Spinal fusion has been used for many years to treat painful conditions in the spine. It is the surgical technique to stabilize the spinal bones, or vertebrae, and the disc, or shock absorber, between the vertebrae. The goal of spinal fusion is to create solid bone between two or more vertebrae. A solid fusion between two vertebrae stops the movement between the bones. This reduces pain from motion and nerve root inflammation.

Spinal fusion may be recommended for conditions such as spondylolisthesis (slippage of one vertebra over the one below), spondylolysis (a defect in the bony ring of a vertebra), degenerative disc disease, or for recurrent disc herniations despite multiple surgeries. Spinal fusion may also be used to treat segmental instability, to correct spine curvature, and to relieve pressure on nerve roots or your spinal cord caused by bone spurs or spinal stenosis.

Procedure

There are a number of different surgical approaches to spinal fusion. Your doctor will choose the best approach for you depending on your particular spinal problem and the part of your spine that is affected. Over the years there have been dramatic improvements in the way spinal fusion operations are performed. One major improvement has been the development of fixation devices.

Cervical Spinal Fusion

There are two types of cervical fusion procedures: anterior cervical fusion, and posterior cervical fusion. In the anterior cervical fusion, the operation is done from the front of your neck. In the posterior cervical fusion, the operation is done through an incision in the back of your neck.

Most neck problems are from a degenerative, or aging, condition of the spine. Degenerative disc disease and cervical stenosis are two diagnoses that can lead to pressure on the spinal cord or nerve roots. Surgery to remove this pressure can be done from the front (anterior) or back (posterior) of the neck. Doctors use the anterior approach more often because the pressure is usually on the front portion of your nerves or spinal cord.

Anterior Cervical Fusion

Anterior cervical discectomy is one of the most common surgical procedures for problems in the cervical spine. The term discectomy means to “remove the disc.” This procedure is routinely used to relieve pressure on a spinal nerve or the spinal cord cause by a herniated disc. Discectomy is also done when your doctor intends to fuse two or more bones of your neck together. This procedure of disc removal and fusion (described below) is often used to treat degenerative problems (called spondylosis) in the neck.

In your cervical spine, the disc is usually removed from the front. An incision is made in the front of your neck beside your trachea (windpipe). The muscles are moved to the side. The arteries and nerves in your neck are also protected. Upon reaching the front of your spine, your doctor will use an X-ray to identify the problem disc. This disc is removed all the way back to your spinal cord. If any bone spurs are found sticking off the back of the vertebrae and your doctor thinks they may also be causing you pain, they may be removed at the time of surgery. Great care is taken to not damage your spinal cord and nerve roots.

After the disc between your vertebrae has been removed, a cervical fusion is performed. The space where the disc was taken out is filled with a block of bone graft taken from the top rim of your pelvis at the time of surgery. Bone graft taken from your own body is called autograft. Your doctor may obtain bone from a source other than your body, called allograft. This is bone that is taken from organ donors and stored under sterile conditions until needed for operations such as spinal fusion. The bone goes through a rigorous testing procedure, similar to a blood transfusion, before being used for fusion surgery.

Placing a bone graft between two or more vertebrae causes the vertebrae to fuse or grow together, creating a solid piece of bone. This halts motion between the problem vertebrae, creating stability in the joint. Cervical fusion is used to treat cervical fractures, dislocations, and other pathologies. It is also used to correct deformities in your neck.

The anterior cervical fusion may also be done in a way that spreads your vertebrae apart a bit to help restore the space between them. This is done to recreate the normal height of the disc space and to restore the normal inward curve of your neck (called lordosis). Increasing the distance between the vertebrae also widens the opening (foramina) where the nerves come out of your spine. Restoring the size of the foramina is done to relieve pressure and irritation from bone spurs where the nerves pass through the foramina.

Posterior Cervical Fusion

Posterior cervical fusion is done through the back of your neck. A bone graft is placed on the back surface of the problem vertebrae. During the healing process, the vertebrae grow together creating a solid piece of bone. This type of fusion is used in the cervical spine for fractures and dislocations. It is also used to correct deformities in your neck.

Lumbar Spinal Fusion

When performing a lumbar spinal fusion, your doctor may use an anterior (from the front) lateral (from the side), or posterior (from the back) approach, a combination of the two approaches, or a Transforaminal Lumbar Interbody Fusion (TLIF) approach. Lateral and posterior approaches may also be performed using a minimally invasive surgery (MIS) technique in which your doctor makes 2 small incisions instead of one large incision. This enables the surgery to be potentially performed in less time, and with less trauma and pain than traditional surgical approaches.

Anterior Lumbar Fusion

The anterior interbody approach allows your doctor to remove the intervertebral disc from the front and place bone graft between the vertebrae. This operation is usually done by making an incision in your abdomen just above your pelvic bone. The organs in your abdomen, such as your intestines, kidneys and blood vessels, are moved to the side to allow your doctor to see the front of your spine. Your doctor then locates the problem disc and removes it. Bone graft is placed into the area between your vertebrae where the disc has been removed.

Posterior Lumbar Fusion

The posterior approach to lumbar spinal fusion is done from your back. This approach can be just a fusion of the vertebral bones or it can include removal of the problem disc. If the disc is removed, it is replaced with a bone graft. Your doctor will move your spinal nerves to one side and insert the bone graft between the vertebral bodies. This is called a posterior lumbar interbody fusion.

With a posterior approach, an incision is made in the middle of your lower back over the area of your spine that is going to be fused. Your muscles will be moved to the side so your doctor can see the back surface of your vertebrae. Once your spine is visible, the lamina of the vertebra is removed to take pressure off the dura and nerve roots. This allows your doctor to see areas of pressure on your nerve roots caused by bone spurs, a bulging disc, or thickening of the ligaments. Your doctor can remove or trim these structures to relieve the pressure on your nerves. Once your doctor is satisfied that all pressure has been removed from your nerves, a fusion is performed. When operating from the backside of your spine, the most common method of performing a spinal fusion is to place strips of bone graft over the back surface of your vertebrae.

Combined Lumbar Fusion

Working between the vertebrae from your back has limitations. Your doctor is limited by the fact that your spinal nerves are constantly in the way. These nerves can only be moved a slight amount to either side. This limits your doctor’s ability to see the area. There is also limited room to use instruments and place implants. For these reasons, many doctors prefer to make a separate incision in your abdomen and actually perform two operations–one from the front of your spine and one from the back. The two operations are usually performed at the same time, but they may be done several days apart.

Transforaminal Lumbar Interbody Fusion (TLIF)

TLIF is an adaptation of a posterior lumbar interbody fusion. There are several potential advantages of TLIF over the standard posterior approach:

• The procedure can allow your doctor to fuse both the anterior and posterior portions of your spine through a single posterior surgical approach.
• TLIF increases the chance for a successful fusion due to the larger area for bone graft placement. Bone graft can be placed both in the area behind the vertebrae, to the side of the vertebrae, and in the disc space between the vertebrae.
• Because the approach to your disc space and spinal canal with TLIF is from your side, this allows your doctor to perform the operation with minimal stretching of your nerve roots. The exposure of your spinal canal is done from one side only.
• TLIF uses a special spacer that is placed between your vertebrae to help restore the space between the vertebrae (the disc space). This can help reduce irritation and pressure on your nerve roots from bone spurs and thickened ligaments that can be a source of leg pain.

During the TLIF procedure, your doctor will have you lie face down on a special surgery frame. This position allows your doctor to operate on the back of your spine. It also lets your abdomen relax, which reduces blood loss during the procedure. General anesthesia is used, meaning you will be asleep during surgery.

Your doctor will begin by making a vertical incision over the section of your spine to be fused. Some doctors perform the TLIF surgery “percutaneously,” which means that only two small openings are made in your skin. Your skin, muscles, and soft tissues will be gently pulled aside.

Your doctor will work through the main incision and separate your tissues over the back part of your iliac crest. A small amount of bone will be taken from this part of your pelvis and prepared for use later in the TLIF procedure.

Your doctor will then prepare to insert pedicle screws into your spine by watching on a fluoroscope (an X-ray that can be seen on a video screen) to determine the exact spot to place the screws. The screws are inserted through the pedicle bones of the vertebrae to be fused. For example, if two vertebrae are in need of fusion, four screws are used, two on the left and two on the right.

Your doctor will enlarge the opening around your nerve root, called the foramen. A special instrument called an osteotome will be used to cut the bone that surrounds this passageway. Enlarging the foramen takes pressure off your nerve root and gives your doctor more room to do the TLIF surgery through the foramen. (“Transforaminal” means through the foramen). The nerve root going through the foramen is gently moved aside for the remainder of the TLIF procedure.

The disc between the two vertebrae to be fused will be removed. Your doctor will remove the disc by inserting a special surgical tool called a rongeur through the foramen and cutting a small “window” into the back of the disc. The disc is removed by working from the back toward the front of the disc space. When the disc and remaining fragments have been cleared away, your doctor will prepare the bony surfaces of the vertebral bodies where the disc was removed.

The surface of the vertebral body within the disc space is called the end plate. By peeling off the end plate with a curette, your doctor causes bleeding to occur. The bleeding is needed to stimulate healing of the bone graft that will be placed into the interbody space.

Your doctor will prepare to insert the spacer into the disc space between the vertebral bodies. The spacer, sometimes called a “fusion cage,” is made either of bone, titanium, or carbon fiber reinforced polymer. Most spacers are hollow so bone graft material (taken from your pelvis or in the form of a bone substitute) can be packed inside the spacer. Your doctor will measure the size of the disc space to ensure the best fit of the spacer.

Working through the foramen, your doctor will insert the bone graft material into the front half of the disc space. Next, a spacer will be placed into the back half of the disc space and pushed as far as possible to the opposite side. A second spacer will be inserted next to the first spacer. This completes the steps for fusing the front of the vertebrae (the anterior column).

Stabilizing the posterior column is completed by adding strips of bone graft along the side and the back of the vertebrae to be fused. Next, your doctor will realign the surgery frame to give your low back a slight inward curve. Metal rods or plates are attached to the pedicle screws. Tightening this instrumentation compresses the vertebrae to be fused.

After Spinal Fusion

A minimum of three months is needed for the bones to fuse together and become solid. Yet the bone graft will continue to mature for one to two years. Your doctor may have you wear a rigid brace for up to three months to keep your spine still and make sure the bones fuse. You may not require a rigid brace after fusion with instrumentation.

Most patients are able to return home when their medical condition is stabilized, usually within one week after fusion surgery. Limit your activities to avoid doing too much too soon. Avoid bending, lifting, twisting, and driving for at least six weeks.