What happens during the operation?
Patients are given a general anesthesia to put them to sleep during most spine surgeries. As you sleep, your breathing may be assisted with a ventilator. A ventilator is a device that controls and monitors the flow of air to the lungs.
During surgery the patient usually kneels face down on a special operating table. The special table supports the patient so the abdomen is relaxed and free of pressure. This position reduces blood loss during surgery. It also gives the surgeon more room to work.
Two measurements are made before surgery begins. The first measurement ensures that the surgeon chooses a fusion cage or bone wedge that will fit inside the disc space. To correctly size the fusion cage or bone wedge, the surgeon uses an X-ray image to measure the disc space in a healthy disc, above or below the problem segment.
Second, to size the length of the pedicle screws, a CT scan is used to measure the length of the pedicle bone on the back of the vertebrae to be fused. The CT scan is a special type of X-ray that lets doctors see slices of bone tissue. The machine uses a computer and X-rays to create these slices.
To begin the procedure, an incision is made down the middle of the low back. The tissues just under the skin are separated. Then the small muscles along the sides of the low back are moved aside, exposing the back of the spinal column. Next, the surgeon takes an X-ray to make sure that the procedure is being performed on the correct vertebrae.
The bone graft is prepared. When autograft (bone taken from your body) is used, the same incision made at the beginning of the surgery can be used. The surgeon reaches through the first incision and opens the tissues that cover the back of the pelvis. An osteotome is used to cut the surface of the pelvis bone. An instrument is used to gather a small amount of the pelvis bone. The graft material is prepared and will later be packed into the fusion cages. The tissues covering the pelvis bone are sutured.
Then the surgeon prepares to implant bone graft into the space between the vertebral bodies. The surgeon removes the lamina bones that cover the back of the spinal canal. Next, the surgeon cuts a small opening in the ligamentum flavum, an elastic ligament separating the lamina bones and the spinal nerves. Removing the ligamentum flavum allows the surgeon to see inside the spinal canal. The nerves are checked for tension where they exit the spinal canal. If a nerve root is under tension, the surgeon enlarges the neural foramen, the opening where the nerve travels out of the spinal canal.
The surgeon locates the spot where the pedicle screws are to be placed. A fluoroscope is used to visualize the pedicle bones. A fluoroscope is a special type of X-ray that allows the surgeon to see an X-ray picture continuously on a TV screen. The surgeon uses the fluoroscope to guide one screw through the back of each pedicle, one on the left and one on the right.
The nerve roots inside the spinal canal are then pulled aside with a retractor so the problem disc can be examined. With the nerves held to the side, the surgeon is able to see the disc where it sits just in front of the spinal canal.
A hole is cut into the rim of the back of the disc. Forceps are placed inside the hole in order to clean out disc material within the disc. Reamers and scrapers are used to open up and remove additional disc material.
The surgeon prepares the disc space where the fusion cages or bone wedges are to be inserted. Special spreaders hold the two vertebral bodies apart. A layer of bone is shaved off the flat surfaces of the two vertebrae, causing the surfaces to bleed. Bleeding stimulates the bone graft to heal the bones together.
Adequate room is needed to get the bone graft implants through the spinal column and into the disc space. The nerve roots must be pulled as far to the side as possible to open up enough space.
With the disc space held apart by the spreaders, the surgeon has enough room to place the bone graft between the two vertebral bodies. For the fusion cage method, the surgeon packs two cages with bone taken from the pelvis bone or with a suitable bone substitute. Two cages are inserted, one on the left and one on the right. When allograft bone wedges are used, the surgeon inserts the wedges and aligns them within the disc space.
The surgeon uses a fluoroscope to check the position and fit of the graft.
The spreaders used to hold the disc space apart are released. Then the doctor tests the graft by bending and turning the spine to make sure the graft is in the right spot and is locked in place.
Some surgeons add strips of bone graft along the back of the vertebrae to be fused. This is called posterolateral fusion. The bones that project out from each side of the back of the spine are called transverse processes. The back surface of the transverse processes are shaved, causing the surfaces to bleed. Small strips of bone, usually taken from the pelvis bone at the beginning of the surgery, are placed over the transverse processes. The combination of this graft material with the pedicle screws helps hold the spine steady as the interbody fusion heals.
A drainage tube may be placed in the wound. The muscles and soft tissues are then put back in place. The skin is stitched together. The surgeon may place you in a rigid brace that straps across the chest, pelvis, and low back to support the spine while it heals.