Spinal instrumentation is a method of keeping the spine rigid after spinal fusion surgery by surgically attaching hooks, rods, and wire to the spine in a way that redistributes the stresses on the bones and keeps them in proper alignment while the bones of the spine fuse.
Spinal instrumentation is used to treat instability and deformity of the spine. Instability occurs when the spine no longer maintains its normal shape during movement. Such instability results in nerve damage, spinal deformities, and disabling pain. Scoliosis (scoliosis) is a side-to-side spinal curvature. Kyphosis is a front-to-back curvature of the upper spine, while lordosis is an excessive curve of the lower spine. More than one type of curve may be present.
Spinal deformities may be caused by:
- birth defects
- Marfan syndrome
- neuromuscular diseases
- severe injuries
- idiopathic scoliosis (Idiopathic scoliosis is scoliosis of unknown origin. About 85% of cases occur in girls between the ages of 12 and 15 who are experiencing adolescent growth spurt.)
Spinal instrumentation provides a stable, rigid column that encourages bones to fuse after spinal fusion surgery. Its purpose is to aid fusion. Without fusion, the metal will eventually fatigue and break, and so instrumentation is not itself a treatment for spine deformity.
Different types of spinal instrumentation are used to treat different spinal problems. Although the details of the insertion of rods, wires, screws, and hooks vary, the purpose of all spinal instrumentation is the same—to correct and stabilize the backbone while the bones of the spine fuse. The various instruments are all made of stainless steel, titanium, or titanium alloy.
The oldest form of spinal instrumentation is the Harrington rod. While it was simple in design, it required a long period of brace wearing after the operation, and did not allow segmental adjustment of correction. The Luque rod was developed to avoid the long postoperative bracing period. This system threads wires into the space within each vertebra. The risk of injury to the nerves and spinal cord is higher than with some other forms of instrumentation. Cotrel-Dubousset instrumentation uses hooks and rods in a cross-linked pattern to realign the spine and redistribute the biomechanical stress. The main advantage of Cotrel-Dubousset instrumentation is that because of the extensive cross-linking, the patient may not have to wear a cast or brace after surgery. The disadvantage is the complexity of the operation and the number of hooks and cross-links that may fail.
Several newer systems use screws that are embedded into the portion of the vertebra called the pedicle. Pedicle screws avoid the need for threading wires, but carry the risk of migrating out of the bone and contacting the spinal cord or the aorta (the major blood vessel exiting the heart). During the late 1990s, pedicle screws were the subject of several high-profile lawsuits. The controversies have since subsided, and pedicle screws remain an indispensible part of the spinal instrumentation. Many operations today are performed with a mix of techniques, such as Luque rods in the lower back and hooks and screws up higher. A physician chooses the proper type of instrumentation based on the type of disorder, the age and health of the patient, and the physician's experience.
The surgeon strips the tissue away from the area to be fused. The surface of the bone is peeled away. A piece of bone is removed from the hip and placed along side the area to be fused. The stripping of the bone helps the bone graft to fuse.
After the fusion site is prepared, the rods, hooks, screws, and wires are inserted. There is much variation in how this is done based on the spinal instrumentation chosen. Once the rods are in place, the incision is closed.
Spinal fusion with spinal instrumentation is major surgery. The patient will undergo many tests to determine the nature and exact location of the back problem. These tests are likely to include
- x rays
- magnetic resonance imaging (MRI)
- computed tomography scans (CT scans)
In addition, the patient will undergo a battery of blood and urine tests, and possibly an electrocardiogram to provide the surgeon and anesthesiologist with information that will allow the operation to be performed safely. In Harrington rod instrumentation, the patient may be placed in traction or an upper body cast to stretch contracted muscles before surgery.
After surgery, the patient will be confined to bed. A catheter is inserted so that the patient can urinate without getting up. Vital signs are monitored, and the patient's position is changed frequently so that bedsores do not develop.
Recovery from spinal instrumentation can be a long arduous process. Movement is severely limited for a period of time. In certain types of instrumentation, the patient is put in a cast to allow the realigned bones to stay in position until healing takes place. This can be as long as six to eight months. Many patients will need to wear a brace after the cast is removed.
During the recovery period, the patient is taught respiratory exercises to help maintain respiratory function during the time of limited mobility. Physical therapists assist the patient in learning self-care and in performing strengthening and range-of-motion exercises. Length of hospital stay depends on the age and health of the patient, as well as the specific problem that was corrected. The patient can expect to remain under a physician's care for many months.
Spinal instrumentation carries a significant risk of nerve damage and paralysis. The skill of the surgeon can affect the outcome of the operation, so patients should look for a hospital and surgical team that has a lot of experience doing spinal procedures.
Since the hooks and rods of spinal instrumentation are anchored in the bones of the back, spinal instrumentation should not be performed on people with serious osteoporosis. To overcome this limitation, techniques are being explored that help anchor instrumentation in fragile bones.
After surgery there is a risk of infection or an inflammatory reaction due to the presence of the foreign material in the body. Serious infection of the membranes covering the spinal cord and brain can occur. In the long term, the instrumentation may move or break, causing nerve damage and requiring a second surgery. Some bone grafts do not heal well, lengthening the time the patient must spend in a cast or brace or necessitating additional surgery. Casting and wearing a brace may take an emotional toll, especially on young people. Patients who have had spinal instrumentation must avoid contact sports, and, for the rest of their lives, eliminate situations that will abnormally put stress on their spines.
Many young people with scoliosis heal with significantly improved alignment of the spine. Results of spinal instrumentation done for other conditions vary widely.
Morbidity and mortality rates
Mortality rate for spinal fusion surgery is less than 1%. Neurologic injury may occur in 1–5% of cases. Delayed paralysis is possible but rare.
Not all patients require instrumentation with their spinal fusion. For some patients, a rigid external brace can provide the required rigidity to allow the bones to fuse.
"Cotrel-Dubousset Spinal Instrumentation." In Everything You Need to Know About Medical Treatments. Springhouse, PA: Springhouse Corp., 1996.
"Harrington Rod." In Everything You Need to Know About Medical Treatments. Springhouse, PA: Springhouse Corp., 1996.
National Scoliosis Foundation. 5 Cabot Place, Stoughton, MA 020724. (800) 673-6922. http://www.scoliosis.org
Orthogate [cited July 1, 2003]. http://owl.orthogate.org/ .
Tish Davidson, A.M. Richard Robinson
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Spinal instrumentation is performed by a neurosurgical and/or orthopedic surgical team with special experience in spinal operations. The surgery is done in a hospital under general anesthesia. It is done at the same time as spinal fusion.
QUESTIONS TO ASK THE DOCTOR
- What types of instrumentation will I be receiving?
- Why is this the best choice for my condition?
- How long will I be immobilized?
- Should I receive physical therapy to help me regain lost strength and mobility?