Anterior Thoracic Fusion
Fusion is the process of joining bones with bone grafts, adding bone graft or bone graft substitute to an area of the spine to set up a biological response that causes the bone to grow between the two vertebral elements and thereby stop the motion at that segment. The fusion process essentially “tricks” the body into thinking it has a fracture.
THE GENERAL PROCEDURE:
1. Surgical approach
- The skin incision is made in the side of the chest.
- The space between the ribs is entered.
- The lungs and great vessels are retracted off of the spine.
- This part of the procedure is often performed by a thoracic surgeon.
2. Disc removal
- A needle is then inserted into the disc space and an x-ray is done to confirm that the surgeon is at the correct level of the spine.
- After the correct disc space has been identified on x-ray, the disc is then removed by first cutting the outer annulus fibrosis (fibrous ring around the disc) and removing the nucleus pulposus (the soft inner core of the disc).
- Dissection is carried out from the front to back of the disc. Part of the rib head may need to be resected to allow complete disc removal.
3. Preparation of the fusion bed
After the disc is removed, a space remains between the vertebral bodies.
Disc space shavers and spacers may be used to template the height, width, and depth of bone graft that is needed.
The surfaces of the vertebral bodies are meticulously prepared for bone graft by burring any irregularities. This allows surface area for the ingrowth of bone.
4. Bone graft and fusion
Since it is desirable to maintain the height of the disc space, a "structural" piece of bone may be used in the lower thoracic spine if necessary.
Bone graft is often obtained from the pelvis (the iliac crest). Alternatively, allograft and/or bone graft substitutes and extenders can be used.
Next, the bone graft material is placed in the disc space.
However, a solid fusion is not always achieved. There are a few factors that patients can control that are important in determining whether or not a fusion grows in solidly, including:
- Smoking cessation. It is generally advisable to quit smoking prior to a spinal fusion procedure, as nicotine is a direct toxin to bone graft and will prevent the bone from forming.
- Limited motion. Bone forms better if motion is limited, so patients are often advised to avoid bending, lifting, and twisting for up to three months after spinal fusion surgery depending on the amount of instability.
The principal risk from a fusion is that it does not heal. In general, allograft bone does not heal quite as well as autograft bone, but both yield good results when used in the anterior thoracic spine.
The principal disadvantage with using autograft bone is that another incision needs to be made over the hip to harvest the bone graft. Possible complications associated with taking out bone graft include:
- Graft site chronic pain (which happens 10% to 25% of the time)
- Hip fracture
- Damage to the lateral femoral cutaneous nerve (a sensory nerve that supplies sensation to the front of the thigh)
The chances of a complication increase with the size of the bone graft. The bone graft is an important part of the procedure, and many patients find the bone graft harvest site to be more painful than the cervical surgery itself.
If allograft is used, there is a theoretical risk of transmission of an infection from a donor. The risk of contracting HIV from a graft has been estimated to be between 1 in 200,000 to 1 in 1 million.
In skilled hands, this is a very safe procedure. Possible reported risks and complications of anterior thoracic fusion may include:
- Injury to the lungs or diaphragm
- Damage to the spinal cord
- Continued pain
- Adjacent disc disease
- Graft extrusion
Since the thoracic cavity is entered, a chest tube will be needed for a few days post-operatively. The activity level is gradually increased once the chest tube is out (assuming stability of the spine has been established).
Since fusion will take at least three months to set up, some type of immobilization is recommended. Thoracolumbar bracing is often used after surgery for comfort and to decrease the motion of the spine to allow fusion. Patients are encouraged to walk as much as possible but to avoid lifting or binding early on. Strengthening and physical therapy can be started at three months post-operative if the fusion appears to be progressing well.
It should be noted that the time to fusion can vary, and usually use of the patient’s own bone or use of instrumentation can result in a quicker fusion. It usually takes approximately three months, but can take up to 6 to 9 months, for the bone graft to fuse to the vertebral body bone. Heavy lifting, overhead work, and work away from the body are usually limited until the fusion is noted to be solid.
Signs of infection like swelling, redness or draining at the incision site, and fever should be checked out by the surgeon immediately. Keep in mind, everybody is different, and therefore the amount of time it takes to return to normal activities is different for every patient. Discomfort should decrease a little each day. Most patients will benefit from a postoperative exercise program or supervised physical therapy after surgery.
Radiographs will be taken at regular intervals to assess fusion. Further studies such as CT scan, MRI, or CT myelogram may be necessary if the pain continues or if the fusion is in question.