Lumbar Cage Fusions

Cages have been used since 1992 to help fuse lumbar vertebra. The lumbar vertebrae are the bones of the spinal column. These bones are separated from each other by the lumbar disc, which acts as a shock absorber. The spinal cord and spinal nerves run behind the vertebral bodies and disc and are covered by surrounding bone and joints that are on the back, or posterior, portion of the spine. Traditionally, spinal fusions were performed by laying bone graft on the back, or posterior, aspects of the spine in hopes that they would fuse, or heal, together. However, this necessitated incisions in the back and division of the back musculature. The fusion rate with laying bone on the spine only, was less than optimal and therefore, the systems to make the spine more rigid, such as screws and rods, were developed. However, these screw and rod systems also necessitated muscle dissection from the back of the spine.

Fusion cages were developed to allow the spine to heal between the vertebral bodies rather than along the back of the spine. By completely removing the disc, which is between vertebral bodies, and replacing it with cages and bone graft, a more stable fusion can be obtained. In years past, fusions of this type were attempted by replacing the disc with bone graft alone. However, this led to collapse of the graft and a poor rate of healing. By utilizing metallic or carbon fiber fusion cages, structural support is obtained from the cage while healing goes on both through the cage and around the cage with bone graft or bone substitutes.

The most common indication for an anterior fusion with cages is disc degeneration. In this case, a patient will have chronic low back pain because his disc has degenerated, or collapsed. This is often a consequence of a previous disc herniation, an injury where the disc is torn, or from accelerated degeneration from repetitive trauma, smoking or obesity. Patients often complain of chronic back pain that may radiate into the buttocks. Non-surgical treatments for degenerative disc disease include aggressive and active physical therapy for strengthening the trunk musculature, the short-term use of a brace or corset, anti-inflammatory medications. Most patients can learn to live with their back pain from disc degeneration through non-operative means. However, for those patients in whom pain is severe or unremitting, surgical fusion is an option.

Disc Degeneration

Post-operative X-Rays showing cage placement (LT cages)

Anterior fusion means the surgeon will approach the spine from the front. The surgeon can access the spine anteriorly using a vertical transperitoneal incision (vertical incision through the abdominal cavity), a horizontal retroperitoneal incision (horizontal incision behind the abdominal cavity), or laparoscopically.

Open Incision

In all three of these techniques, the internal abdominal organs are moved away from the spine and allow the surgeon to completely remove the disc from the front. This gives the surgeon a better view of the disc and allows a more complete disc removal. In surgery, the disc height can be restored by distracting within the disc space. This not only restores the normal height and alignment of the vertebral column but also provides stability by placing the ligaments at that level in tension. This new distracted height is then maintained by threading the fusion cages in place. These cages are first filled with bone graft, which can then heal between the end plates of the vertebral bodies. Finally, the space between the cages and in front of the cages is filled with bone graft as well.

Typically, patients remain in the hospital from one to three days after a fusion with cages. They are allowed to walk and perform non-impact aerobic exercise as tolerated within the first few weeks. More aggressive weight lifting and trunk exercises can usually be begun within six to eight weeks. In my experience, by performing an anterior interbody fusion with cages and avoiding any posterior incision, patients recover more quickly and more completely after this type of fusion.

Cage fusions have good results for one or two level degenerative disc disease. For fusions that entail more than two levels of fusion, the results of cage fusions have been less than optimal. Cage fusions are not indicated for high-grade spondylolisthesis or patients with marked instability of the spine.

Most patients, once their fusion is solid, can return to normal activities. I typically do not restrict my patients from aggressive athletic activities or manual labor following a successful fusion. Obviously, the individual indications for this procedure must be discussed with your spinal surgeon.