Spinal fusion literally involves a fusion of two (or even more) vertebrae to limit motion between the specific vertebrae. The vertebrae can be fused together with bone grafts (from the hip bone or newer bone substitutes) and/or with metal rods.
About half of all spinal fusions are done in the neck area and half involve the lower back (lumbar spine).
The fused vertebrae act as “one” solid bone, allowing virtually no movement between them and reducing spinal flexibility to some extent. If motion and friction between the affected vertebrae are the cause of pain, elimination of these factors will reduce the pain. A fusion can also halt the progress of scoliosis or other spinal deformities.
Why a spinal fusion?
Spinal fusion may be necessary to treat:
- Injuries to the vertebrae;
- In cases where mere cutting away of the protruding part of a slipped or herniated disc between the vertebrae does not sufficiently alleviate pain and pressure on the nerve.
The process by which a normal shock-absorbing disc becomes a slipped disc, can be explained as follows:
A degenerative disc loses its cushioning effect and can no longer function as a shock absorber between two vertebrae. The space between the vertebrae narrows, as well as the holes (foramen) that the nerve bundles (to and from the limbs, controlling movement and sensation) pass through. Too narrow spaces will cause pressure on the nerves, leading to pain and loss of sensation or movement of the affected limb.
Then, as if the back pain is not enough, over years the facet joints of the vertebrae become arthritic and develop bony spurs. This process (called spondylosis) causes further narrowing of the foramen and progresses until the facet joints are so arthritic that they lose all their cartilage and, with no cartilage protection, begin to slide directly on one another.
This process of “bare back” sliding allows the vertebrae to slip on one another, resulting in further narrowing of the foramen. This regression (called spondylolisthesis) is worse when standing and walking.
Note that when a nerve is pinched by a ruptured disc, the protruding section of the disc can be removed surgically in order to relieve pressure on the nerve (this is a laminectomy, followed by a discectomy). However, when disc becomes very degenerate and the nerve is pinched by newly formed bony spurs, spinal fusion is the better option.
The holes through which the nerves exit can be indirectly enlarged by a fusion because the screws between the fused vertebrae can be distracted before they’re locked onto the connecting rods.
How does a surgeon “fuse” two or more vertebrae?
The operation is done under general anaesthetic, with the patient lying on his/her stomach. The same approach is used as with a laminectomy or a discectomy.
The surgeon will remove the lamina precisely as in the case with a laminectomy, then the protruding section of the disc as in the case with a discectomy.
The next step of the operation – “fusing” together two or more vertebrae – follows. The surgeon will remove pieces of bone (in a process called bone grafting) from the patient’s hip and place these pieces in the newly created space between the vertebrae. Screws and rods may be inserted to provide immediate stability to the spine and allow early mobilisation after the surgery.
After the surgery, the adjacent vertebrae should be held as stable and immobile as possible to allow the bones to fuse together. The spine can be immobilised by internal fixation devices or by external braces or a cast, or both.
It will take the bone about three months to fuse together.
Can anything go wrong during surgery?
Virtually no form of surgery is without risk. The risks after spinal fusion surgery can be listed as infection, bleeding, urinary difficulties (retention) and temporary problems with the passing of stools (or rather the lack thereof). The fusion may fail to incorporate (pseudoarthritis). This occurs especially in smokers and revision surgery may be necessary.
How to prepare for surgery and the time after surgery
Make sure you are in good mental and physiological health before your operation. Follow an exercise programme to make your body as strong as possible before surgery and continue with this (at first under the watchful eye of a physiotherapist) as soon as possible. Stop smoking as far in advance of the operation as possible and don’t start smoking after the operation.
Tell your doctor about all the herbal remedies you’re taking and stop taking them because St John’s Wort, arnica, omega fatty acids and others can cause bleeding problems during surgery.
Pain after surgery is common, but can and should be treated effectively with tablets, injections or patient-controlled analgesia.
It is of incredible importance that the fused spine be kept in proper alignment. You will be taught how to move, sit, stand and walk correctly. The spine must never be twisted in order to roll over or to move, but the entire body should be moved as a unit. At the time of discharge from hospital, you may be wearing a back brace or cast and you will need help and support from family members with bathing and getting in and out of bed or picking things up from the floor.
Reviewed by Dr Pradeep Makan, orthopaedic surgeon, Melomed Gatesville and Life Vincent Pallotti Hospital in Cape Town and part-time lecturer in the department of orthopaedic surgery at the University of Cape Town, 2010.