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
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.
Summary
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.
