Approximately 80% of Australians
experience significant back pain at least once in their
lifetime, and for many people, spinal disorders are
a lifelong problem. The personal and monetary costs
associated with this widespread problem are staggering.
One of the main causes of back pain and spinal disorders
is the degeneration of spinal discs. Disc degeneration
is painful and often difficult to treat. One of the
most promising surgical options currently being developed
is the use of artificial discs.
What is a Spinal Disc?
The spaces between each vertebra in your spine (spinal
discs) serve as shock absorbers for your spine. As we
age, these discs can deteriorate. When this happens,
they lose their shock absorbing abilities and cause
pain and wear and tear on the vertebra.
Current Treatment Options
Non-surgical options for people with neck and back pain
include rest, heat, pain medications, physical therapy
and chiropractic manipulation. Unfortunately, these
treatments fail in a significant number of patients.
When non-surgical treatment options fail, surgery is
often the next step. This usually means spinal fusion
surgery. Unfortunately, there are a number of drawbacks
to undergoing a spinal fusion. First, the bone does
not always heal or "fuse" correctly. In fact,
the overall success rates for these procedures range
from 48% to 89%. Second, a spinal fusion at one or more
levels causes stiffness and decreased motion of the
spine. Third, spinal fusion at one or more levels increases
stress to the rest of the spine. This transferred stress
may cause new problems to develop at the other levels,
which may lead to additional back surgery. Clearly,
an alternative treatment option is needed.
Artificial Discs - Why Are They Important?
We have all heard of hip and knee replacement surgeries.
These procedures have provided much relief for people
who suffer from pain in those areas. But what about
spinal disc replacement? Is this the option millions
of back pain sufferers have been looking for?
The idea of spinal disc replacement is not new. It
was first attempted 40 years ago when a surgeon implanted
stainless steel balls in the disc spaces of over 100
patients. These pioneering efforts were followed by
more than a decade of research on the degenerative processes
of the spine, spinal biomechanics and biomaterials before
serious efforts to produce an artificial disc resumed.
Today, artificial disc replacement is considered experimental
and is not yet approved by the Food and Drug Administration
(FDA), but the goal is to develop a device that will
eliminate the pain caused by disc degeneration while
maintaining mobility and function.
Artificial Discs - Key Design Features
There are a variety of factors designers must keep in
mind as they develop an artificial disc. The device
must be able to maintain proper intervertebral spacing,
allow for the full range of motion and provide stability.
It must also come in a variety of sizes to accommodate
patient height and spacing needs. Like a natural disc,
the artificial disc must act as a shock absorber, especially
if it is going to be used in several levels of the spine
at one time. Finally, the artificial disc must be very
durable. The average age of a patient needing a lumbar
disc replacement is about 35 years. This means that
to avoid the need for revision surgery, the artificial
disc must last at least 50 years. It has been estimated
that an individual takes 2 million steps per year and
bends 125,000 times; therefore, over the 50-year life
expectancy of the artificial disc, there would be over
106 million cycles. This estimate does not even include
the subtle disc motion that occurs with the 6 million
breaths we each take per year!
What an artificial disc is made from is also an important
factor in the development of this technology. It must
be made of materials that are safe to be implanted in
the human body, not cause allergic reactions and not
damage other parts of the spine. Also, it would be ideal
if the artificial disc were made of a material that
could easily be seen on an x-ray or other imaging test.
This would make it easier for the surgeon to monitor
the effectiveness of the artificial disc over time.
Artificial Discs - What's on the Horizon?
A prospective, randomised, controlled IDE clinical
study performed in the US consisted of 541 patients.
There were 276 enrolled in the investigational group
(Prestige Disc Replacement), with the 265 control patient's
receiving a bone and plate fusion.The Prestige group
had statistically lower rates of secondary surgical
procedures related to revisions and supplemental fixations.
Their neurological success rate was statistically higher
than the control group.Of great interest is the fact
patients returned to work more quickly in the investigational
group, with a median time of 45 days (16 days earlier
than the control group). The full report of this IDE
study and the determination of the safety and effectiveness
of the Prestige Device can be found on the FDA website.
here to see the FDA report.
Today, there are 4 "types" of artificial
disc being studied and tested. They include composite,
hydraulic, elastic and mechanical discs. The following
is a brief description of each.
The most widely implanted disc to date is a composite
disc called the Link SB Charité disc (now the
CHARITÉ Artificial Disc, DePuy Spine, Inc.).
This device is made of a polyethylene spacer and two
separate metal endplates and comes in different sizes.
It also has a ring around it to make it visible on an
Photo: CHARITÉ Artificial Disc
Courtesy of DePuy Spine, Inc.
This device has been implanted in over a thousand European
patients with relatively good results. Additional clinical
trials using this device are ongoing in Europe, the
United States, Argentina, China, Korea and Australia.
There have also been several reports on results from
an artificial cervical disc, which was originally developed
in Bristol, England. This disc is a ball and socket
type device made of stainless steel. It is secured to
the vertebra with screws. The results of this device
have been good and additional clinical studies are being
conducted in Europe and Australia.
The Bryan Cervical Disc System is
another composite type artificial disc designed with
a low friction, wear resistant, elastic nucleus with
two anatomically shaped metal plates. A flexible membrane
forms a sealed space and contains a lubricant to reduce
friction and wear and tear. The implant allows for normal
range of motion and comes in five sizes. The initial
clinical experience with the Bryan Total Cervical Disc
Prosthesis has been promising.
Photo: Bryan Cervical Disc Prosthesis
Hydraulic Artificial Discs
Hydraulic artificial discs have a
gel-like core covered with a tightly woven polyethylene
"jacket". Before it is implanted, the pellet-shaped
hydrogel core is compressed and dehydrated to minimize
its size. Once it is implanted, the outer woven covering
allows fluid to pass through to the core, which immediately
begins to absorb fluid and expand. Most of the expansion
takes place in the first 24 hours after surgery, although
it takes about 4-5 days for the hydrogel core to reach
maximum expansion. Placement of two hydraulic implants
within the disc space generally provides the lift that
is necessary to restore and maintain disc space height
in most patients.
Photo: PDN Prosthetic Disc Nucleus
This type of artificial disc has been extensively
tested, and the results have been good. Currently, further
clinical evaluation is being conducted in Europe, South
Africa and the United States.
Elastic type artificial discs are
made of a rubber core bonded to two titanium endplates.
The results of testing have been mixed. 6 patients who
received this type of artificial disc were evaluated
after a minimum of 3 years, at which time the results
were graded as follows: 2 excellent, 1 good, 1 fair,
and 2 poor. One of the elastic discs in a patient with
a poor result developed a tear in the rubber. Since
that time, a second-generation elastic disc made of
silicone rather than rubber has been approved for more
Photo: Acroflex Disc
Several pivot or ball type artificial discs have been
developed for the lumbar spine. One device, made of
metal-hinged plates with an interposed spring, has been
tested on sheep with good results. Another device has
a polyethylene core and metal endplates with two vertical
wings. Patients who received this implant reported good
to excellent results.
The Future is Bright
Artificial spinal disc replacement is not only possible
but it has the potential of revolutionising the treatment
of spinal degeneration and providing relief to millions
of back pain sufferers. The development of an artificial
disc still has many challenges, but the results from
initial efforts have been promising. Stay tuned
future is bright.
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