Fusion is the process of joining bones with bone grafts, adding bone graft or bone graft substitute 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. The fusion process essentially "tricks" the body into thinking it has a fracture (see spinal disorders).

Anterior lumbar fusion is performed from the front of the low back regions for reasons such as instability of the spine, degenerative disc disease, or fracture. The goal with fusion is to stabilize the spine so that pain or deformity is reduced.

There are multiple different methods for obtaining a spinal fusion. One method is the Anterior Lumbar Interbody Fusion (ALIF). This type of spinal fusion, which involves placing bone graft with or without allograft strut graft or instrumentation in the disc space, has a long history. 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.

The General Procedure:

1. Surgical approach
• A three-inch to five-inch incision is made on the left side of the abdomen or alternatively in the midline. 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 surgeon access to the front of the spine.
• Alternatively, the peritoneum can be cut and the abdominal contents retracted to approach the spine. This is performed most commonly at L5-S1.
• The large blood vessels that continue to the legs (aorta and vena cava) are gently retracted off of the anterior spine.This part of the procedure is often performed by a general or vascular surgeon.
  
  
2. Disc removal
• A needle is then inserted into the disc space and an x-ray is done to confirm that the surgeon is at the correct level of the spine
• After the correct disc space has been identified on x-ray, the disc is then removed by first cutting the outer annulus fibrosis (fibrous ring around the disc) and removing the nucleus
pulposus (the soft inner core of the disc)
• Dissection is carried out from the front to back of the disc.
  
  
3. Preparation of the fusion bed
• After the disc is removed, a space remains between the vertebral bodies.
• Disc space shavers and spacers may be used to template the height, width, and depth of bone graft that is needed.
• The surfaces of the vertebral bodies are meticulously prepared for bone graft by burring any irregularities. This allows surface area for the ingrowth of bone.
  
  
4. Bone graft and fusion
• Cancellous bone graft is often obtained from the pelvis (the iliac crest). Alternatively or additionally, bone graft substitutes and extenders can be used.
• Since the lumbar disc spaces are tall, often a structural, weight-bearing component is necessary to maintain the disc height and lordosis. An allograft strut structural bone or instrumentation is often employed.
• The combination of the structural component (either allograft strut or instrumentation) and non-structural component (cancellous autograft or allograft and/or bone graft substitutes or extenders) are inserted into the disc space.

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 results with either procedure are equivalent and the type of approach used should depend mostly on which procedure the surgeon is most comfortable using.

However, a solid fusion is not always achieved. There are a few factors that patients can control that are important in determining whether or not a fusion grows in solidly, including:

• Smoking cessation. It is generally advisable to quit smoking prior to a spinal fusion procedure, 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 often advised to avoid bending, lifting, and twisting for three months after spinal fusion surgery.