Anterior Lumbar Interbody Fusion
INTRODUCTION:
Spinal fusion is a technique used to stabilize the spinal bones or vertebrae. The goal of a lumbar fusion is to create a solid bridge of bone between two or more vertebrae. Solid fusion occurs when two bones mend or weld together, much like a broken bone healing in a cast. Spinal fusion may be recommended for conditions such as spondylolisthesis (forward slippage of one vertebra on top of another), degenerative disc disease, recurrent disc herniation, or failed previous surgery.
ANATOMY:
The spine is composed of individual bones called vertebrae. Lumbar vertebrae are stacked one on top of another and are separated by the interior discs, which act as cushions or shock absorbers. A circle of bone extends from the vertebral body back around the sac of nerves and spinal cord. This circular protective tube of bone, called the spinal canal, protects the spinal cord and spinal nerves. In the lumbar spine the spinal nerves exit the spinal canal between the vertebrae at each level. Two nerves exit each level, one on the left and one on the right. These nerves exit through openings called foramina [Figure 1].
The interbody space is the disc space that is located between the vertebral bones. An interbody fusion is a surgical procedure performed by the spine surgeon to help a variety of spinal conditions. Interbody fusion involves placement of fusion cages and bone graft into the area between two vertebral bodies [Figure 2 & Figure3]. Interbody fusion is shown to be effective for achieving fusion. The intervertebral cage may be made from a variety of material including metal, carbon fiber, or bone. Bone graft and bone healing protein are also placed within the cage and within the interbody space to allow for bony healing to occur between two vertebrae, forming a solid fusion.
The cage helps in several ways. First, it separates and holds the two vertebrae apart. This makes the opening around the nerve roots at that level larger, relieving pressure on the nerves. The intervertebral cage and fusion also can be used to correct spinal deformity and restore proper alignment. Intervertebral cages can be implanted from the front or back of the spine. The location of the surgery is dependent on the specific anatomy of each patient, as well as the location and amount of pressure that may be occurring around the nerves in the spinal canal.
In some cases, an interbody fusion can be performed without the need for additional instrumentation or stabilization. For patients undergoing interbody fusion in the lumbar spine, anterior plating placed on the lumbar spine can be used for additional stability. An interbody fusion may also be used as part of a posterior instrumented fusion procedure using pedicle screws and instrumentation.
Figure 1:
Figure 2:
Anterior lumbar interbody fusion is generally used to treat back or leg pain caused by degenerative disc disease. The surgeon will stabilize the spine by fusing vertebrae together with bone graft material. The procedure is performed through a three to five inch incision on the stomach. Two common approaches are over the center of the stomach or slightly to the side. The damaged disc is partially removed. Some of the disc wall is left behind to help contain the bone graft material. A metal cage implant filled with bone graft is placed in the empty disc space. This realigns the vertebral bones, lifting the pressure off the pinched nerve roots. In some patients this will be enough to secure the vertebrae [Figure 3]. In other cases, the surgeon may need to implant a series of screws and rods along the back of the spine for additional support. Over time the bone graft will grow through and around the implants, forming a bone bridge that connects the vertebra below and above. This solid bone bridge is called a fusion.
Figure 3:
A lumbar fusion may be appropriate for patients with low back pain or pinched nerves. The specific decision to perform a lumbar interbody fusion depends on a number of factors that will be discussed with your spinal specialist.
