Spinal fusion is a procedure that promotes the fusing, or growing together, of two or more vertebrae in the spine.
Spinal fusion is performed to:
The goal of spinal fusion is to unite two or more vertebrae to prevent them from moving independently of each other. This may be done to improve posture, increase ability to ventilate the lungs, prevent pain, or treat spinal instability and reduce the risk of nerve damage.
According to the American Academy of Orthopaedic Surgeons, approximately a quarter-million spinal fusions are performed each year, half on the upper and half on the lower spine.
The spine is a series of individual bones called vertebrae, separated by cartilaginous disks. The spine is composed of seven cervical (neck) vertebrae, 12 thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region.
While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow tube containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae.
The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together.
The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae.
While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle "S" shape. The spine curves in at the lumbar region, back out at the thoracic region, and back in at the cervical region.
Abnormal side-to-side curvature of the spine is termed scoliosis. An excessive lumbar curve is termed lordosis, and an excessive thoracic curve is kyphosis. "Idiopathic" scoliosis is the most common form of scoliosis; it has no known cause.
Scoliosis and other curves can be caused by neuromuscular disease, including Duchenne muscular dystrophy. Progressive and perhaps uneven weakening of the spinal muscles leads to gradual inability to support the spine in an upright position. The weight of the upper body then begins to collapse the spine, inducing a curve. In addition to pain and disfigurement, severe scoliosis prevents adequate movement of air into and out of the lungs. Scoliosis also occurs in cerebral palsy, due to excess and imbalanced muscle activity pulling on the spine unevenly.
Idiopathic scoliosis, which occurs most often in adolescent girls, is usually managed with a brace that wraps the abdomen and chest, allowing the spine to develop straight. Spinal fusion is indicated in patients whose curves are more severe or are progressing rapidly. The indication for surgery in cerebral palsy is similar to that for idiopathic scoliosis.
Spinal fusion in Duchenne muscular dystrophy is usually indicated earlier than in otherwise healthy adolescents. This is because these patients lose ventilatory function rapidly through adolescence, making the surgery more dangerous as time passes. Surgery should occur before excess ventilatory function is lost.
As people age, their disks become less supple and more prone to damage. A herniated disk is one that has developed a bulge. The bulge can press against nerves located in the spinal cord or exiting from it, causing pain. Disks can also degenerate, losing mass and thickness, allowing vertebrae to contact each other. This can pinch nerves and cause pain. Disk-related pain is very common in the neck, which is subject to constant twisting forces, and the lower back, which experiences large compressive forces. In these cases, spinal fusion is employed to prevent the nerves from being damaged. The offending disk is removed at the same time. A fractured vertebra may also be treated with fusion to prevent it from causing future problems.
Sometimes, spinal fusion is used to treat back pain even when the anatomical source of the problem cannot be located. This is usually viewed as a last resort for intractable and disabling pain.
Spinal fusion is performed under general anesthesia. During the procedure, the target vertebrae are exposed. Protective tissue layers next to the bone are removed, and small chips of bone are placed next to the vertebrae. These bone chips can either be from the patient's hip or from a bone bank. The chips increase the rate of fusion. Using bone from the patient's hip (an autograft) is more successful than banked bone (an allograft), but it increases the stresses of surgery and loss of blood.
Fusion of the lumbar and thoracic vertebrae is done by approaching from the rear, with the patient lying face down. Cervical fusion is typically performed from the front, with the patient lying on his or her back.
Many spinal fusion patients also receive spinal instrumentation . During the fusion operation, a set of rods, wires, or screws will be attached to the spine. This instrumentation allows the spine to be held in place while the bones fuse. The alternative is an external brace applied after the operation.
An experimental treatment, called human recombinant bone morphogenetic protein-2, has shown promise for its ability to accelerate fusion rates without bone chips and instrumentation. This technique is only available through clinical trials at a few medical centers.
Spinal fusion surgery takes approximately four hours. The patient is intubated (tube placed in the trachea), and has an IV line and Foley (urinary) catheter in place. At the end of the operation, a drain is placed in the incision site to help withdraw fluids over the next several days. The fusion process is gradual and may not be completed for months after the operation.
A potential candidate for spinal fusion undergoes a long series of medical tests. In patients with scoliosis, x rays are taken over many months or years to track progress of the curve. Patients with disk herniation or degeneration may receive x rays, MRI studies, or other tests to determine the location and extent of injury.
Patients in good health may donate several units of their own blood in preparation for surgery. This may be done between six weeks and one week prior to the operation. The patient will probably be advised to take iron supplements to help replace lost iron in the donated blood. Sunburn or sores on the back should be avoided prior to surgery because they increase the risk of infection.
A variety of medical tests will be done shortly before surgery to ensure that the patient is in good health and prepared for the rigors of surgery. Blood and urine tests, x rays, and possibly photographs documenting the curvature will be done. An electroencephalogram (EEG) may be performed to test nerve function along the spine.
The patient will be admitted to the hospital the evening before surgery. No food is allowed after midnight, in order to clear the gastrointestinal tract, which will be immobilized by anesthesia.
The patient will stay in the hospital for four to six days after the operation.
Post-operative pain is managed by intravenous pain medication. Many centers use patient-controlled analgesia (PCA) pumps, which allow patients to control the timing of pain medication.
For several days after the operation, the patient is unable to eat or drink because of the lasting effects of the anesthesia on the bowels. Fluids and nutrition are delivered via the IV line.
The nurse helps the patient sit up several times per day, and assists with other needs as well. Physical therapy begins several days after the operation.
Most activities are restricted for several weeks. Strenuous activities such as bike riding or running are usually resumed after six to eight months. The surgical incision should be protected from sunburn for approximately one year to promote healing of the scar.
Spinal fusion carries a risk of nerve damage. Rarely, delayed paralysis can occur, probably from loss of oxygen to the spine during surgery. Infection may occur. Bone from the bone bank carries a small risk of infection with transmissible diseases from the bone donor. Anesthesia also poses risks. Unsuccessful fusion (pseudoarthrosis) may occur, leaving the patient with the same problem after the operation.
Spinal fusion for scoliosis is usually very successful in partially or completely correcting the deformity. Spinal fusion for pain is less uniformly successful because the cause of the pain cannot always be completely identified.
Unsuccessful fusion may occur in 5–25% of patients. Neurologic injury occurs in less than 1–5% of patients. Infection occurs in 1–8%. Death occurs in less than 1% of patients.
Bracing and "watchful waiting" is the alternative to scoliosis surgery. Disk surgery without fusion is possible for some patients. Strengthening exercises and physical therapy may help some back pain patients avoid back surgery.
Neuwirth, M.D., Michael. The Scoliosis Sourcebook. New York: McGraw-Hill, 2001.
Robinson, Richard. "Setting the Record Straight." Quest Magazine 4, no.1 (1997). http://www.mdausa.org/publications/Quest/q41scoliosis.html
National Scoliosis Foundation. (800) NSF-MYBACK (673-6922). http://www.scoliosis.org .
Spinal fusion is performed by an orthopedic surgeon or neurosurgeon in a hospital setting.