What is Spinal Fusion?
Spinal fusion is one of the most common types of spinal stenosis surgeries and is designed to help stabilize the spine whilst decompressing spinal nerves and/or the spinal cord. This procedure involves the use of a bone graft using bone taken from elsewhere in the patient’s body (usually the hip bone), known as an autograft, or an allograft where donor bone from a bone bank is used.
These pieces of bone are positioned between vertebra to restore or maintain intervertebral height and relieve pressure on the nerves caused by spinal stenosis. To hold the bone in place the surgeon may use screws, rods, metal plates or cages which prevent the bone graft from moving out of position before new bone growth fuses the graft to existing bone in the spine.
Why Choose Spinal Fusion?
This form of spinal stenosis treatment is helpful where a patient has symptoms of nerve compression caused by degenerative disc disease that has led to a decrease in the space between vertebra. It is also useful for those with back pain and other symptoms of spinal stenosis, such as sciatica, caused by painful motion between vertebra.
Allografts vs. Autografts
Patients whose own bone is used tend to have a more successfuly outcome from spinal fusion as the body more easily recognizes its own cells and can heal faster. Allografts are also associated with a lower risk of infection as well as rejection of the graft (which may necessitate further surgery). In some cases a person’s own bone may be of such poor quality, or the harvesting procedure too risky for them, that an allograft or bone substitute is the better option. This may be the case for those with bone-depleting diseases like osteopenia.
Those who are unable to have an autograft and who undergo an allograft usually require immunosuppressive drugs to prevent the body rejecting donor bone. The bone is typically harvested from cadavers and may be added to autograft bone. This bony material is usually refined and contained within a small cage that is positioned and secured between vertebra.
Although the removal of bone from the hip (or elsewhere) during an autograft means that the patient has an additional incision the risk of infection does appear to be lower with autografts than allografts. This is because immunosuppressive drugs taken to prevent donor bone rejection also compromise the body’s ability to fight off infection.
In summary, allografts are associated with less pain while autografts are considered more reliable and predictable.
Synthetic Bone Substitutes for Spinal Fusion
Synthetic bone substitutes offer another option for those undergoing spinal stenosis fusion surgery. These can be helpful where insufficient bone is available for larger spinal fusion procedures, where a patient cannot have their own bone harvested, or where a matching allograft is unavailable. Bone graft substitutes include bone morphogenic protein (BMP) or demineralized bone matrix (DBM). BMP relies on bone-forming proteins in the body, while DBM is a manufactured product made from cortical bone that has had its calcium and phosphorus removed.
Read more about spinal fusion recovery and prognosis.