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.
Spinal fusion has been used for many years to treat painful conditions in the lumbar spine. Over the past decade, there have been dramatic improvements in the way that spinal fusion operations are performed. One major improvement has been the development of fixation devices.
In order to understand your symptoms and treatment choices, it is helpful to start with a basic understanding of the anatomy of your low back. This includes becoming familiar with the various parts that make up the lumbar spine and how these parts work together.
Only when all other conservative treatments have failed will your doctor suggest fusion surgery. Several back conditions may require a spinal fusion, including:
- Degenerative Disc Disease
- Spinal Instability
- Spine Curvature
- Spondylolysis and Spondylolisthesis
Degenerative Disc Disease
Degeneration of the discs between one or more vertebrae may require a spinal fusion of the vertebrae on both sides of thedegenerative disc. The intervertebral discs are flat, round “cushions” that act as shock absorbers between each vertebra in the spine. The disc allows motion to occur between each vertebra. Removing a degenerated disc and allowing the two vertebrae to fuse together can reduce pain.
Each spinal segment is like a well-tuned part of a machine. All of the parts should work together to allow weight bearing, movement, and support. When one segment deteriorates to the point of instability, it can lead to localized pain and difficulties.
Segmental instability occurs when there is too much movement between two vertebrae. The excess movement of the vertebrae can cause pinching or irritation of nerve roots. It can also cause too much pressure on the facet joints, leading to inflammation. It can cause muscle spasms as the paraspinal muscles try to stop the spinal segment from moving too much. The instability eventually results in faster degeneration in this area of the spine.
Lumbar fusion may be needed for conditions such as scoliosis and kyphosis, where the spine has an abnormal curve. These spine deformities may result from congenital or degenerative spine conditions. A lumbar fusion may be suggested to stabilize the spine and correct the problem.
Spondylolysis and Spondylolisthesis
Spondylolisthesis is the term used to describe when one vertebra slips forward on the one below it. This usually occurs because there is a spondylolysis (defect) in the vertebra on top. There are two main parts of the spine that keep each vertebra aligned-the disc and the facet joints. When a spondylolisthesis occurs, the facet joint can no longer hold the vertebra back. The intervertebral disc may slowly stretch under the increased stress and allow the upper vertebra to slide forward. A fusion may be used for both conditions to stop motion in the problem vertebrae, where there is a spondylolysis.
During a spinal fusion, a bone graft is used to join two or more vertebrae. The vertebrae grow together during the healing process, creating a solid piece of bone. The bone graft helps the vertebrae heal together, or fuse. The bone graft is usually taken from the pelvis at the time of surgery. However, some surgeons prefer to use bone graft from a bone bank (called allograft).
Your surgeon can use an anterior (from the front) approach, a posterior (from the back) approach, or a combined approach to lumbar fusion surgery.
In some cases, it may be best to consider placing the bone graft between the vertebral bodies. The anterior interbody approach allows the surgeon to remove the intervertebral disc from the front and place the bone graft between the vertebrae.
This operation is usually done by making an incision in the abdomen, just above the pelvic bone. The organs in the abdomen, such as the intestines, kidneys, and blood vessels, are moved to the side to allow the surgeon to see the front of the spine. The surgeon then locates the problem disc and removes it. Bone graft is placed into the area between the vertebrae where the disc has been removed.
The posterior approach is done from the back of the patient. 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. The surgeon moves the spinal nerves to one side and inserts 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 the lower back over the area of the spine that is going to be fused. The muscles are moved to the side so that the surgeon can see the back surface of the vertebrae. Once the spine is visible, the lamina of the vertebra is removed to take pressure off the dura and nerve roots. This allows the surgeon to see areas of pressure on the nerve roots caused by bone spurs, a bulging disc, or thickening of the ligaments. The surgeon can remove or trim these structures to relieve the pressure on the nerves. Once the surgeon is satisfied that all pressure has been removed from the nerves, a fusion is performed. When operating from the backside of the spine, the most common method of performing a spinal fusion is to place strips of bone graft over the back surface of the vertebrae.
Working between the vertebrae from the back of the patient has limitations. The surgeon is limited by the fact that the spinal nerves are constantly in the way. These nerves can only be moved a slight amount to either side. This limits the ability to see the area. There is also limited room to use instruments and place implants. For these reasons, many surgeons prefer to make a separate incision in the abdomen and actually perform two operations-one from the front of the spine and one from the back. The two operations are usually performed at the same time, but they may be done several days apart.
In the past, spinal fusions of the lumbar spine were performed without any internal fixation. The surgeon simply roughed up the bone, placed bone graft material around the vertebrae, and hoped the bones would fuse. Sometimes, patients were placed in a body cast to try to hold the vertebrae still while healing. The patient was lucky to have a 70 percent chance of successful fusion.
Surgery of the spine continues to be a challenging and difficult area. The vertebrae are small, so there is not much room to place small instruments. Also, many nerves can get in the way of putting screws into the vertebral body. And a large amount of stress is put on the lower back, so finding a metal device that is able to hold the bones together can be difficult.
Over the past two decades, some very inventive devices have been designed that have changed the way surgeons perform spinal fusions.
Pedicle Screws and Rods
The surgeon may use some type of metal screws, plates, and rods to hold the vertebrae in place while the spine fusion heals. Designed to stabilize and hold the bones together while the fusion heals, these devices have greatly improved the success rate of fusion in the lower back.
A new type of device, called an intervertebral fusion cage, can be used to perform a spinal fusion between two or more vertebrae. These implants are designed to spread the two vertebrae apart while the fusion heals.
Like all surgical procedures, operations on the spine may have complications. Because the surgeon is operating around the spinal cord and nerves, back operations are always considered extremely delicate and potentially dangerous. You should take time to review the risks associated with spine surgery with your doctor. Make sure you are comfortable with both the risks and the benefits of the procedure planned for your treatment.
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.
Your doctor may have you attend physical therapy beginning a minimum of six weeks after surgery. A well-rounded rehabilitation program assists in calming pain and inflammation, improving your mobility and strength, and helping you do your daily activities with greater ease and ability. Therapy sessions may be scheduled up to three times each week for eight to 12 weeks.
The goals of physical therapy are to help you
- Learn ways to manage your condition and control symptoms
- Improve flexibility and core strength
- Learn correct posture and body movements to protect the fusion
- Return to work safely