Spinal fusion is surgery to permanently connect two or more vertebrae in the spine, eliminating motion between them.
Spinal fusion involves techniques designed to mimic the normal healing process of broken bones. During spinal fusion, a bone or a bone-like material is placed within the space between two spinal vertebrae. Metal plates, screws, and rods may be used to hold the vertebrae together, so they can heal into one solid unit.
Why Spinal Fusion is done
Spinal fusion permanently connects two or more vertebrae in the spine to improve stability, correct a deformity or reduce pain. Spinal fusion may be recommended to treat:
- Deformities of the spine. Spinal fusion can help correct spinal deformities, such as a sideways curvature of the spine (scoliosis).
- Spinal weakness or instability. The spine may become unstable if there’s abnormal or excessive motion between two vertebrae. This is a common side effect of severe arthritis in the spine. Spinal fusion can be used to restore spinal stability in such cases.
- Herniated disc. Spinal fusion may be used to stabilize the spine after removal of a damaged (herniated) disc.
Best candidates for spinal fusion surgery
Spinal fusion surgery prevents movement between vertebrae that are rubbing against each other and causing pain. After the procedure, the two vertebrae are fused together, eliminating any movement between them. The pain should then completely disappear, permanently. Surgical procedures are usually performed only as a last resort for treating back pain, spinal fusion can lead to a long-term pain resolution for the right candidate.
Spinal fusion is considered one of the best procedures to treat people with:
- Lumbar Spondylolisthesis: Spondylolisthesis is a condition in which one of the bones in the vertebra (vertebra) slips forward and out of place. This may occur anywhere along the spine but is most common in the lower back (lumbar spine). In some people, this causes no symptoms at all. Others may have back and leg pain that ranges from mild to severe.
- Lumbar degenerative disc disease: This condition weakens one or more of the vertebral discs. The discs normally act as a cushion between the vertebrae. Degenerative disc disease can develop as a natural part of the aging process, but it may also result from injury to the back and become a source of chronic pain. One of the first symptoms is experiencing pain, numbness or tingling in the legs. Strong pain tends to come and go. Bending, twisting and sitting may make the pain worse. Lying down often relieves pressure on the spine.
- Scoliosis: This condition causes a normally straight spine to curve. Scoliosis can limit the ability to move normally. If it’s severe enough, it can cause pain. A misshapen rib cage can restrict normal lung growth and the ability to breathe.
- Unstable or weak spine
- Spine fractures
Whether spinal fusion is right for a patient or not depends on a number of factors. Ideally, the procedure works best when there are only two vertebrae involved in the movement that requires the graft. With a one-level fusion, any limitations in movement may not even be noticed.
Spinal fusion on two levels may feel slightly restrictive, depending on the location of the afflicted vertebrae. Once beyond two levels, though, a marked reduction in movement will definitely be noticed. Typically, a spinal fusion of three or more levels is reserved for those with the most severe spinal handicaps, such as extensive scoliosis or life-threatening deformities.
Important additional factors to be considered before spine fusion surgery
In addition to the spinal fusion approach used, there are a number of other factors to be considered before spine fusion surgery which include:
The posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) surgeries allow for placement of bone or a cage in the disc space, increasing the fusion rate and hopefully a better clinical outcome. There is a more neurologic risk because of the need to retract the nerve roots, however, major nerve injury is unusual. It has the advantage of placing a structural graft or device in the major weight-bearing part of the spine while avoiding a separate incision.
Traditionally, bone graft has been harvested from the patient’s own iliac crest (pelvis) to stimulate the fusion site. Cadaver bone often is useful in anterior fusions, but it works poorly in posterior applications. Recent advances have allowed spine surgeons to decrease the need for bone graft harvest by using substitutes, e.g., collagen sponges, demineralized bone matrix, platelet-derived growth factors and, most promising, bone morphogenic protein (BMP).
The bone morphogenic protein currently in use (Infuse) has FDA approval for anterior application only. Further research is ongoing to document the utility of these products, which allow for diminished patient trauma that can occur from harvesting bone graft from the patient’s own hip.
- Minimally invasive surgery (MIS) :
Much work is in development to try to decrease the trauma patients incur by placing pedicle screws through smaller incisions. This is thought to result in less muscle trauma and allow for more rapid recovery after spine surgery.
Caution needs to be exercised, however, as even though a technique is less traumatic, if the spine fusion rate is much lower, then there is really not an advantage. Also, it has yet to be demonstrated that minimally invasive spine fusion systems actually cause better outcomes than some other surgical techniques used in the traditional open approach.
Spine Fusion Risks and Complications
Spinal fusion is generally a safe procedure. But as with any surgery, spinal fusion carries the potential risk of complications.
Potential risks and complications include:
- Poor wound healing
- Blood clots
- Injury to blood vessels or nerves in and around the spine
- Pain at the site from which the bone graft is taken
- Possible re-operation
- Lack of a solid fusion
The most common risk of any of the modern spine fusion surgery techniques is the failure to relieve lower back pain symptoms following the surgery. In the best of all situations, this risk occurs in a minimum of 20% of spine fusion surgeries. The likelihood of this result becomes even more frequent with fusions of three or more levels. This outcome is commonly referred to as “failed back surgery syndrome”.
There is also a risk that the vertebrae may not fuse together following the surgery, called pseudoarthrosis. With modern techniques happens in approximately 5% to 10% of spine fusion surgeries.
It is well documented in the medical literature that people who smoke have a lower rate of successful spine fusion.
If pedicle screws are used, there is a risk that the screws may break or become loose and may require further surgery to remove or revise the screws and rods.
Anterior grafts and cages can migrate or subside, which may require repeat spine surgery. If the anterior devices were placed anteriorly (from the front), rather than through a PLIF or TLIF (approaches through the back), it is safest to do this revision spine fusion surgery with a posterior approach (from the back).
All spine fusion surgeries have the potential for complications. Thankfully, most of the complications occur infrequently. The complications that can occur include those that would be associated with any type of surgery, such as infection, bleeding, and anesthetic complications.
Another potential complication of spine fusion surgery in the low back includes any type of nerve damage. Although major loss of the strength and sensation to the legs or loss of bowel or bladder control can occur, it is rare. In a small percentage of men who have an anterior fusion, an infrequent complication results in difficulties with ejaculation following spine fusion surgery. There is a small plexus of nerves in front of the L5-S1 disc space that helps control ejaculation. If these nerves are affected (which can happen 1% of the time) then a valve will not close that forces the ejaculate outward. The ejaculate then follows the path of least resistance, which is up into the bladder. The most significant side effect of this complication is that it is very difficult to complete conception. The potency is not affected, and the sensation of sex is still largely the same. In about half of cases, this complication resolves over the course of about 6 to 12 months.
The success rate of spine fusion surgery
Spinal fusion operation is a salvage procedure. For patients with disabling back pain and leg pain, significant benefits can be obtained with successful spinal fusion.
Studies indicate that the patient’s pain is improved 60% to 70% after spinal fusion surgery and approximately 80% of patients undergoing spinal fusion surgery are satisfied with the surgical result.
An accurate diagnosis is needed with clear objectives for the procedure. The rest of the responsibility for success rests with the candidate. Spinal fusion works best on people who do not smoke, are not obese and live a relatively healthy lifestyle.
As with any surgery, a positive attitude goes a long way. Additionally, it is important to be motivated to pursue the physical therapy that’s going to be required following the spinal fusion surgery. Spinal fusions almost always lead to pain-free living with little or no residual complications.