THE EMERGENCE OF ARTIFICIAL DISC REPLACEMENT

More than 80% of Americans will experience significant back pain at least once in their lives. The personal and monetary impact can be staggering. A major cause of back pain is the degeneration of the shock absorbers, discs that are positioned in between the bony vertebral bodies of the spine. disc degeneration can be painful and often difficult to treat long term. A promising surgical option recently approved by the FDA is the use of artificial discs.

The Spinal Disc

Spinal discs lie between the vertebrae in our spines, serve as shock absorbers, and allow range of motion. However, as early as in our 30's, these discs begin to lose their water content and then degenerate. This results in disc flattening, tearing or fraying which can irritate nerve endings resulting in back pain. We are not sure why some people experience these changes earlier than others although there is evidence that genetic influences, environmental stresses and accumulations of major and minor trauma can contribute to a painful disc.

Conservative Treatment Options

Initial treatment for a painful disc is always conservative care. Acetaminophen (Tylenol) or non-steroidal anti-inflammatory medications such as aspirin or ibuprofen can be helpful at reducing the back pain. Sometimes it is necessary to take a prescribed anti-inflammatory medication. It can be helpful to undergo trunk strengthening exercise programs in physical therapy since this approach can also reduce pain and help slow the degenerative process. Exercise programs must be continued on a regular basis to make a long term difference. As the trunk muscles become stronger, some of the load across the spine is alleviated and patients feel less back pain. For most patients, their pain and function are improved with nonoperative care to the point that they can lead a reasonably normal life. Unfortunately, a conservative treatment is not always successful at relieving pain and restoring function, which leads to the next step of surgical intervention. Up until this point, the surgical solution meant spinal fusion surgery. Recently, there is also artificial disc replacement surgery for select patients.

Minimally Invasive Procedures

For the small percentage of patients who fail conservative treatments, the minimally invasive options are limited. There is no FDA approved method of effectively reinflating the worn-out disc. Hopefully, this will be an option in the future. Recent interventions include Intra-discal Electrothermal Therapy (IDET) (1997). IDET involves inserting a probe into the affected disc and heating up the outer core of the disc space to 90 degrees (Celsius) for 15-20 minutes in an effort to cauterize tiny nerve endings in the disc, making them less sensitive to pain. Results have been limited, with the latest studies showing only 33-50% patient satisfaction at one year follow up.

Surgical Options

Surgical options for patients with degenerative disc disease who are deemed surgical candidates (not everyone with degenerative discs is a surgical candidate) involve removing the affected disc(s) and either: 1) Fusing the affected segment(s) or 2) Inserting an artificial disc.

Spinal Fusion

The mainstay of surgical treatment for patients with degenerative disc disease who have failed 6-12 months conservative care is to fuse the painful level(s). Spinal fusion entails stopping the motion at a painful motion segment (the joint formed by two vertebral bodies). Fusion takes place by placing bone in between the vertebral bodies. As the bone grows, it fuses the vertebrae together, thus, eliminating the motion at a specific level. Success rates with fusions performed for degenerative disc disease range in the literature between 65 and 93%. It has become the standard of care for discogenic pain and is often very effective in relieving pain.

Bone grafting is required for spinal fusion. The standard in spine surgery is harvesting bone from the patient's pelvis at the time of surgery. However, to improve healing and reduce risk of chronic pain at the bone graft site, other alternatives are now being used. Bone morphogenic protein (BMP) is now frequently used to enhance healing of the fusion. It not only improves the fusion rate but increases its success and often eliminates the need for harvesting bone graft.

Spinal fusion does have its drawbacks. First, the bone does not always heal or "fuse" correctly. A spinal fusion at one or more levels causes stiffness and decreased motion of the spine. Spinal fusion at one or more levels can increase the stress to the rest of the spine. Because of these problems, alternative treatment options such as the artificial disc have been pursued.

Artificial Disc Replacement

Based on the success of other joints in the body successfully treated with joint replacement, efforts began in Europe back in the 1980's to develop an artificial disc replacement. The potential benefit of the artificial disc is to preserve motion of the operated segment allowing the patient more flexibility to bend forward, backward, and rotate or twist. It is also hoped that adjacent levels of the spine will be less likely to become arthritic.

One of these, the SB Charite (Germany) artificial disc, recently completed Food and Drug Administration (FDA) clinical trials and received final approval in the Fall of 2004. Results from the FDA 2 year follow-up were as successful as an anterior fusion. A patient satisfaction survey showed a significant superiority of the Charite group over the fusion group. At 24 months, 88% of patients implanted with the Charite Artificial disc expressed satisfaction with the procedure, compared with 81% of fusion patients. On average, patients implanted with the Charite Artificial disc were discharged from the hospital a half-day sooner than fusion patients.

The materials, cobalt chromium (endplates) and ultra-high molecular weight polyethylene (sliding core) used in the Charite are similar to those used in hip and knee replacements. Patient selection is key to successful artificial disc replacement. Patients must have failed at least six months of conservative treatment such as pain medication or physical therapy. The typical patient is between 18 and 60 years old and has degenerative disc disease between L4-5 and/or L5-S1 with less than 3mm of vertebrae slippage. Candidates suffer from low back pain as the major complaint (rather than leg pain).

The disc is designed to restore disc space height, restore disc flexibility, prevent disc degeneration at adjacent segments and reduce or eliminate pain from motion and improve a patient's functional activities.

The surgical time it takes to implant an artificial disc is similar to that of a fusion, but the procedure is done from the front, as opposed to most fusions which are performed from the back. Typical hospital stay is between 2-4 days, and patients typically have minor motion and lifting restrictions for 6 weeks. These restrictions are less than with a spinal fusion.

Unlike spinal fusion, artificial disc replacement does not yet enjoy long-term follow up results. Considering the young age of most recipients, there is some concern over the long term success rate of these implants. The good news is that if the implant fails to eliminate pain or if the patient develops debilitating pain in the facet (adjacent small joints in the spine) joints, the patient can still undergo a fusion to alleviate the pain.

Artificial disc replacement is an exciting new development. It is a new tool available to certain patients and their spine surgeons to address chronic low back pain due to degenerative disc disease. Research has shown that it can be a benefit to those candidates who have failed conservative management and fit the criteria for patient selection. For more information, you should be evaluated to discuss your options.