Anterior Lumbar Interbody Fusion (ALIF) Surgery

Doctor Cloward first performed an anterior lumbar interbody fusion (ALIF) surgery in the 1950s for treatment of low back pain for degenerative spine conditions. The Cloward procedure did not gain immediate favor because of fairly high nonunion rates (30-40%). In the 1990s, however, there was a resurgence of popularity for anterior (from the front) lumbar interbody fusion surgery because of the advent of new threaded titanium cages that held the disc space better and allowed for a higher fusion rate.

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.

Anterior lumbar interbody fusion description

The anterior lumbar interbody fusion (ALIF) is similar to the posterior lumbar interbody fusion (PLIF), except that in the ALIF the disc space is fused by approaching the spine through the abdomen instead of through the lower back. In the ALIF approach, a three-inch to five-inch incision is made on the left side of the abdomen and the abdominal muscles are retracted to the side (see Figure 1).

Since the anterior abdominal muscle in the midline (rectus abdominis) runs vertically, it does not need to be cut and easily retracts to the side. The abdominal contents lay inside a large sack (peritoneum) that can also be retracted, thus allowing the spine surgeon access to the front of the spine.

Some ALIF procedures will be done using a minilaparotomy (one small incision) or with an endoscope (a scope that allows the surgery to be done through several one-inch incisions).

• The minilaparotomy allows better visualization and can be done with a minimal amount of postoperative pain. Most spine surgeons use the open, minilaparotomy approach.
• The endoscopic approach has more limited visualization, and it usually leads to larger surgical times and carries with it a much higher technical learning curve for the surgeon.

The results with either procedure are equivalent and the type of approach used should depend mostly on which procedure the spine surgeon is most comfortable using. The endoscopic approach has largely fallen out of favor because of the technical difficulties associated with it, and it has not been proven to generally lessen postoperative pain or hasten the healing process.

The large blood vessels that continue to the legs (aorta and vena cava) lay on top of the spine, so many spine surgeons will perform this surgery in conjunction with a vascular surgeon who mobilizes the large blood vessels. After the blood vessels have been moved aside, the disc material is removed and bone graft, or bone graft and anterior interbody cages, is inserted.

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 (see Figure 2).

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.

In general, the principal risk of this type of spine surgery is that a solid fusion will not be obtained (nonunion) and further surgery to re-fuse the spine may be necessary. Fusion rates for an ALIF should be as high as 90-95%.

Non-union rates are higher for patients who have had prior lower back 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 fusion procedure. As long as the joint is stable, and the patient's symptoms are better, more back surgery is not necessary.

Other than non-union, 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.