Charité Artificial Disc and Degenerative Disc Disease
The Charité Artificial Disc (DePuy Spine, Inc.) was approved by the Food and Drug Administration (FDA) on October 26, 2004 for the treatment of severe low back pain due to a damaged or worn out lumbar intervertebral disc.
Charité Artificial Disc (DePuy Spine, Inc.)
Photograph Courtesy of DePuy Spine, Inc.
Conventional Spinal Fusion vs. Disc Replacement
The conventional treatment for a severely degenerated disc is spinal fusion. Fusion involves placing bone graft from the patient's iliac crest (pelvic bone) and inserting metal rods or cages to stabilize the spine. Although spinal fusion can relieve pain by eliminating movement at the motion segment, it can decrease the patient's functional range of motion and may increase stress to the adjacent discs and facet joints.
On the other hand, the artificial disc replaces the damaged disc with some preservation of motion which, theoretically, reduces the stress to the adjacent joints and improves overall motion of the lumbar spine. In addition, following an artificial disc procedure, the patient is encouraged to move their trunk rather than wear a rigid brace, which is often done following a fusion procedure. Early motion may translate into earlier rehabilitation and recovery.
Long-Term Outcome Studies Needed
Although artificial disc technology is a significant advancement in the treatment of degenerative disc disease, long-term outcome studies are necessary to better assess its advantages and disadvantages.
Discogenic Low Back Pain
It should be remembered that the diagnosis of discogenic low back pain (LBP) is elusive and controversial. Often, LBP is associated with other structural changes in the spine such as the muscles, ligaments, facet joints, bone (vertebrae), nerves, and other anatomy. Provocative discography improves the diagnostic accuracy of discogenic LBP but, still it is not precise. Consider the following:
1. Many patients with LBP resulting from structures other than the intervertebral disc, who undergo artificial disc replacement, will have a poor outcome.
2. The majority of discogenic LBP patients will respond well to conservative non-operative treatments that include non-steroidal anti-inflammatory drugs (NSAIDs), prescribed exercise, physical therapy, and injections.
3. Even though intradiscal electrothermal therapy (IDET) is controversial, it can serve to avoid invasive surgical procedures such as fusion or disc replacement in some patients.
4. The number of patients who undergo disc replacement should be relatively small - if surgeons and patients are well-informed about the natural history of LBP and adhere to strict indications for this surgery.
5. The fusion outcomes to treat one- or two-level degenerative disc disease are good in carefully-selected patients. Artificial disc replacement may not offer such long-term advantages.
Artificial disc technology is often compared to total hip or knee arthroplasty, but trunk motion is not completely eliminated even if one- or two disc levels are fused. The motion of the trunk is actually a combination of the motions of multiple spinal vertebrae, the pelvis and hips. Rarely is trunk motion significantly compromised following a successful lumbar fusion of one or two motion segments (levels). In fact, following a successful fusion, trunk motion and function may improve due to the elimination of pre-operative pain.
The exact pathogenesis (i.e. cause) of LBP is unknown, and artificial disc prostheses do not change the posterior facet joints significantly. One of the relative contraindications for disc replacement is "significant facet disease". I submit to you that many patients with discogenic LBP and disc space narrowing exhibit changes in the facet joints. If the facet joint problem is a significant cause of the patient's pain, this new technology will not work initially and continued facet joint osteoarthritis due to preserved motion may affect the clinical outcome later. On the other hand, a fusion procedure eliminates motion at both the intervertebral disc and facet joints. The adjacent joint problem following spinal fusion versus disc replacement is unknown. Long-term studies lasting 10-20 years are needed to answer this question.
Finally, the potential complications associated with artificial disc replacement may include infection, breakage or loosening of the device, dislocation of the implant, and damage to adjacent structures including vital organs such as nerves and blood vessels. Like hip or knee joint replacement surgery, artificial implants may fail over time due to material wear and metal ion release into the blood and vital organs. Loosening of the device is of concern, as artificial discs are implanted in relatively younger patients with longer life expectancies.
Artificial disc replacement is a new and exciting technology. If the surgeon chooses the right patient and performs the surgery correctly, this technology can help patients who suffer from discogenic LBP. I recommend that strict indications for surgery be followed. Further, surgeons must have frank discussions with their patients about the advantages and disadvantages of disc replacement.