There has been a resurgence of popularity for anterior (from the front) lumbar interbody fusion surgery because of the advent of new spinal implants that hold the disc space better and allow 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 spinal 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. For more information, see Spinal Fusion Surgery for Isthmic Spondylolisthesis.
Description of Anterior Lumbar Interbody Fusion Surgery
The anterior lumbar interbody fusion (ALIF) is performed 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 lower abdomen and the abdominal muscles are retracted to the side.
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 without actually entering the abdomen.
There are large blood vessels that continue to the legs and 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.
Advantages of ALIF Surgery
The ALIF approach is advantageous in 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.
Lastly, a much larger implant can be inserted through an anterior approach, and this provides for better initial stability of the fusion construct. 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%, although this should be an uncommon complication in the hands of experienced vascular and spine surgeons.
Retrograde Ejaculation after ALIF Surgery
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.
With retrograde ejaculation, 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.
Other ALIF Considerations
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
- Smoke or are obese
- Have multiple level fusion surgery
- 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.
Indications and Contraindications for Anterior Cages
Because an anterior interbody spine fusion surgery relies on the strength of the vertebral body to keep from subsiding, an absolute contraindication to doing an anterior interbody fusion (without posterior supporting instrumentation) is osteoporosis. The cages do not fail by breaking. They fail because the bone in the vertebral endplates may not be strong enough to support the cages. This leads to a failure of the endplates, with the cage subsiding into the vertebral bodies.
In general, anterior cages are not strictly fixation devices for spine fusion. Pedicle screws used with posterior instrumentation systems provide excellent spinal fixation. Anterior intervertebral devices should be thought of as an interference type of fixation. They are implanted in between the vertebral bodies and do not strictly fixate the two vertebral bodies to each other. Until the bone knits them together, the cage is mostly held by an interference fit.
Because of this difference in mechanics, stand alone anterior fixation is best limited to collapsed disc spaces. It works better at L5-S1 where there is little motion. At L4-L5, there is more flexion/extension motion, and this allows more motion through the cages. Lastly, they work better in one-level spine fusions than two-level fusions, and most spine surgeons feel they should not be used as a stand alone device for three level fusions.
ALIF Video