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Lumbar Spinal Fusion

 

A spinal fusion is designed to stop the motion at a painful vertebral segment, by adding bone graft to that area of the spine. This makes the body think that this is a “broken bone” and healing of the bone, or fusion, occurs. To improve the rate of fusion, instrumentation is often used. This can be thought of as a plaster cast for the broken bone; it keeps the bones still to allow them to heal in the position intended. However, unlike a plaster cast, it is rare to take out the spinal metalwork once it has been put in. It is also used in those patients where the nerves in the spine are squeezed excessively (spinal stenosis) and a full decompression would remove sufficient bone to render the spine too mobile. The fusion stabilizes the spine in this instance.

Lumbar fusion is used in patients with:

  • Degenerative disc disease
  • Spondylolisthesis
  • Unstable spine (tumour, trauma, infection)
  • Deformity (ScoliosisKyphosis)

 

How spine fusion surgery works

In general, a lumbar spinal fusion surgery is most effective for those conditions involving only one vertebral segment. Most patients will not notice any limitation in motion after a one-level spine fusion.   Only in rare cases will a three (or more) level fusion surgery for pain alone be considered, although it may be necessary in cases of scoliosis and lumbar deformity.

When necessary, fusing two segments of the spine may be a reasonable option for treatment of pain. However, spinal fusion of more than two segments for back pain alone is unlikely to provide useful pain relief and is rarely performed.

There are several types of spinal fusion surgery options, including:

1. Posterolateral Fusion

This procedure is done through the back with or without metalwork (screws/rods also called an “instrumented posterolateral fusion”) but no interbody cage. Artificial bone graft or the patient’s own graft (with it’s own good and bad points), may be used for the fusion. After spine fusion surgery, the body tries to repair itself, which usually means growing bone. As the bone graft grows the spinal fusion is achieved and motion at that segment is stopped. Spine surgery instrumentation (metalwork and cages) is sometimes used as an adjunct to obtain a solid fusion. 
However, a solid fusion is not always achieved. There are a couple of key things that patients can do to control to help or hinder a fusion to grow solidly, including:

  • Smoking cessation. It is generally advisable to stop smoking prior to a spinal fusion surgery, 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 advised to avoid bending, lifting, and twisting for three months after spinal fusion surgery (although with metalwork involved, the need for a brace is minimal, which (along with the increased rate of fusion) is the reason for using it).

Most spine fusions will start to fuse within three months, and will continue to get stronger for one to two years. Once a solid fusion is achieved it is very unlikely that it will ever break. Recurrent pain after a successful spine fusion surgery is generally not from the fused level, but can be from any of the other joints.

The principal risk of this type of low back surgery is that a solid fusion will not be obtained (nonunion) and further surgery to re-fuse the spine may be necessary. Nonunion rates of between 10% and 40% have been quoted in the medical literature.

Nonunion rates are higher for patients who have had prior surgery, patients who smoke or are obese, patients who have multiple level spine fusion surgery, and for patients who have been treated with radiation for cancer.

Not all patients who have a nonunion will need to have another fusion procedure. As long as the joint is stable, and the patient's symptoms are better, more back surgery is not necessary.

Other than nonunion, the risks of a spinal fusion surgery include infection or bleeding. These complications are fairly uncommon (approximately 1% to 3% occurrence). In addition, there is a risk of achieving a successful fusion, but the patient's pain does not subside.

It is important to note that with any type of spine fusion surgery, there is a risk of clinical failure (meaning that the patient's pain does not go away) despite achieving a successful fusion.

2. Posterior Lumbar Interbody Fusion (PLIF)

The procedure is done from the back and includes removing the disc between two or more vertebrae and inserting bone (+/- metal cages) into the space created between the two vertebral bodies as well as the posterolateral fusion described above. As with all spinal fusion surgery, a posterior lumbar interbody fusion (PLIF) surgery involves adding bone graft 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.

Unlike the posterolateral gutter fusion, the PLIF achieves spinal fusion in the low back by inserting a bone graft and/or spinal implant (e.g. cage) directly into the disc space. When the surgical approach for this type of procedure is from the back it is called a posterior lumbar interbody fusion (PLIF). A PLIF fusion is often supplemented by a simultaneous posterolateral spine fusion surgery.

It is important to note that with any type of spine fusion surgery, there is a risk of clinical failure (meaning that the patient's pain does not go away) despite achieving a successful fusion.

PLIF spine surgery risks and complications

  • The principal risk of this type of low back surgery is that a solid fusion will not be obtained (nonunion) and further back surgery to re-fuse the spine may be necessary. Fusion rates for a PLIF should be as high as 90-95%. This does not necessarily equate to the “success” of the operation as this is sometimes different for surgeon and patient. It is always useful for both to define what they expect of the operation BEFORE it is done so that this is fully understood from both sides. This is true of any surgical procedure.
  • Nonunion rates are higher for patients who have had prior spine surgery, patients who smoke or are obese, patients who have multiple level fusion surgery, and for patients who have been treated with radiation for cancer.   Not all patients who have a nonunion will need to have another spine fusion procedure. As long as the joint is stable, and the patient's symptoms are better, more back surgery is not necessary.
  • Other than nonunion, the risks of a spinal fusion surgery include infection or bleeding. These complications are fairly uncommon (approximately 1% to 3% occurrence). In addition, there is a risk of achieving a successful spine fusion, but the patient's pain does not subside.

3. Transforaminal Lumbar Interbody Fusion (TLIF)

A transforaminal lumbar interbody fusion (called a TLIF) is essentially like an extended PLIF. It was developed in response to some of the technical problems with a PLIF procedure. The main difference between the two spine fusion procedures is that the TLIF approach to the disc space is by removing one entire facet joint on one side (whereas a PLIF is usually done on both sides by only taking a portion of each of the paired facet joints).

TLIF surgery risks and complications

These are the same as for a PLIF although the risk of injury to the nerve roots or dura is theoretically reduced by the method of the surgical approach.

It is important to note that with any type of spine fusion surgery, there is a risk of clinical failure (meaning that the patient's pain does not go away) despite achieving a successful fusion.

4. Anterior Lumbar Interbody Fusion (ALIF)

Cloward first performed an anterior lumbar interbody fusion (ALIF) surgery in the 1950's for treatment of low back pain for degenerative spine conditions.

While the ALIF is still a widely available spine fusion technique, this type of procedure is often combined with a posterior approach (anterior/posterior fusions) because of the need to provide more rigid fixation than an anterior approach alone provides.

In cases where there is not a lot of instability, an ALIF alone can be sufficient. Generally, this is true in cases of one level degenerative disc disease where there is a lot of disc space collapse. For patients who have a "tall" disc, or for those with instability (e.g. isthmic spondylolisthesis), an anterior approach to spine fusion may not provide adequate stability. In these clinical situations the anterior lumbar interbody fusion may be supplemented with a posterior (from the back) instrumentation and fusion to provide additional support to the fused level of the spine.

The ALIF approach has the advantage that, unlike the PLIF and posterolateral gutter approaches, both the back muscles and nerves remain undisturbed. Another advantage is that placing the bone graft in the front of the spine places it in compression, and bone in compression tends to fuse better.

ALIF surgery potential risks and complications

There is a major risk that is unique to the ALIF approach. The procedure is performed in close proximity to the large blood vessels that go to the legs. Damage to these large blood vessels may result in excessive blood loss. Quoted rates in the medical literature put this risk at 1% to 15%.

For males, another risk unique to this approach is that approaching the L5-S1 (lumbar segment 5 and sacral segment 1) disc space from the front has a risk of creating a condition known as retrograde ejaculation. There are very small nerves directly over the disc interspace that control a valve that causes the ejaculate to be expelled outward during intercourse. By dissecting over the disc space the nerves can stop working, and without this coordinating innervation to the valve, the ejaculate takes the path of least resistance, which is up into the bladder. The sensation of ejaculating is largely the same, but it makes conception very difficult (special harvesting techniques can be utilized). Fortunately, retrograde ejaculation happens in less than 1% of cases and tends to resolve over time (a few months to a year). This complication does not result in impotence, as these nerves do not control erection.

Apart from the risk to the bowel, the other risks of ALIF are the same as other fusion techniques (non-union, re-operation, etc).

It is important to note that with any type of spine fusion surgery, there is a risk of clinical failure (meaning that the patient's pain does not go away) despite achieving a successful fusion.

5. Anterior/Posterior Lumbar Fusion Surgery

Sometimes, both an anterior lumbar interbody fusion and a posterolateral fusion will be performed in the same patient at the same time.

This anterior/posterior (AP) lumbar fusion procedure is usually done for patients with a high degree of spinal instability (e.g. fractures), or in revision surgery (if the initial fusion did not fuse), although some spine surgeons do prefer the anterior/posterior fusion surgery as a primary spinal fusion technique.

Fusing both the front and back provides a high degree of stability for the spine and a large surface area for the bone fusion to occur. Also, approaching both sides of the spine often allows for a more aggressive reduction for patients who have deformity in the lower back (e.g. isthmic spondylolisthesis).

Most times, the anterior (from the front) approach is performed first. By removing the disc material and cutting the anterior longitudinal ligament (which lies on the front of the disc space), the spinal segment is "released" and allows for a more complete reduction. After the anterior and the posterior spinal implants are inserted, this segment is much more stable than even a normal spine segment.

Some spine surgeons feel that if stabilization is achieved both through an anterior and a posterior approach, patients can be mobilized earlier in the postoperative period. Studies have shown that fusing both sides of the spine in the lower back does lead to a very high fusion rate (greater than 95% of these cases will achieve a solid fusion).

A drawback of the procedure is that both an anterior incision in the abdomen and a posterior incision in the low back need to be done. Some spine surgeons prefer to achieve anterior and posterior stability through a PLIF procedure, although there are drawbacks to approaching the disc space through a posterior approach (please see the PLIF section). Spine surgeons with a strong comfort level with doing ALIF surgery generally prefer an anterior/posterior approach.

This technique does provide for very high rates of spinal fusion, but the spine fusion surgery is quite extensive and carries the risks inherent in both the ALIF and the posterolateral gutter fusion procedures.