An incision is made in the middle of the back. The muscles are moved to the side to expose the spine. The joints between the vertebrae are removed to loosen them up. The vertebrae are roughened up so that the body responds by producing new bone. The new bone eventually bridges the gaps between the vertebrae and makes them fuse together. Metal implants -- rods, screws, hooks or wires -- are put in to hold the spine still while the vertebrae fuse.
Bone Grafts
The fusion is augmented with bone graft. This may be obtained from the patient -- known as "autogenous" bone graft and harvested typically from the pelvis, or it can be from a bone bank from a donor -- known as "allogenous." Advantages of autogenous bone graft include more rapid incorporation with the rest of the vertebrae and safety. Disadvantages of autogenous grafts include surgery, which can cause pain and carries its own set of operative risks. The principal risk of allogenous bone graft is risk of infection, in particular hepatitis at the rate of 1 in 1 million and AIDS at the rate of 1 in 10 million. The patient or the patient's parents decide on whether to go ahead with the surgery after a careful discussion of the benefits and risks with the orthopedic surgeon.
Surgery Length
Spinal fusion surgery usually takes four to six hours but the time varies according to the individual patient. The surgeons will take as long as they need to do the job well.
Potential Complications
The potential complications of surgery include:
Bleeding -- This is controlled by cauterizing bleeding vessels during the operation and by using a device that allows the return of blood lost back to the patient at the conclusion of the operation. If it is anticipated that a patient will lose a significant amount of blood, and there is a high likelihood for transfusion, the patient will be asked to donate two units of blood within the month before surgery.
Infection -- This is a risk whenever the skin is cut for any operation. Sterile precautions are taken in the operating room and the patient is given antibiotics before the operation and for 24 hours after. In addition, the incision is washed with a pressurized system before it is closed.
Nerve Injury -- The extent of possible nerve injury can range from a minor injury, such as numbness from compression of a nerve that supplies sensation to the front of the thigh, to a major injury, including paralysis. The risk of major neural injury is well under 1 percent, but it is not zero, so it is essential to have an open and honest dialogue with your orthopedic surgeon about this. The electrical activity of the nerves that transmit signals for sensation and muscle action through the spinal cord is monitored during the procedure. This gives feedback to the surgeon so that the necessary steps can be taken to remedy the problem if it occurs.
Pseudarthrosis -- This means that occasionally -- up to 1 percent of the time in children but more often adults -- the fusion doesn't take, or the vertebrae don't stick together completely. It can take several months or a few years to become apparent. The patient may complain of persistent back pain, there may be progression of the scoliosis after the operation or the implants may fail. When the fusion doesn't take, motion over the long term will cause the metal implants to wear out and ultimately break. Treatment for pseudarthrosis includes exploration of the spine, additional bone grafts and replacement of the implants.