A Flexicore artificial disk, shown as it would be implanted between vertebrae.
Artificial Disks Replace Worn-Out Ones to Stop
Back Pain from Degenerative Disk Disease
I
f your knee or hip wears out, you
can get it replaced. But if a disk in
your spine degenerates, your only
choice is the same one that existed
nearly a century ago: have two adjacent
vertebrae fused together. But soon,
those in chronic pain from degenerative disk disease will have a better
option: permanent replacement with
an artificial disk.
For the past two years, a team led
by Thomas J. Errico, M.D., Associate
Professor of Orthopaedic Surgery and
Neurosurgery and Chief of the Spine
Surgery Service at the Hospital for
Joint Diseases (HJD), has been part of
a clinical trial in which surgeons have
replaced disks in the lower, or lumbar,
spines of nearly 100 patients at HJD.
Dr. Errico is now working on two new
artificial disks, including one for the
upper, or cervical, spine.
A disk, the gel-like connective tissue
between vertebrae, acts as a shock
6
NYU PHYSICIAN / Winter 2004–2005
absorber, rubber band, and ball joint
all in one. It is the element that enables
you to bend, flex, and stretch your
back. But in degenerative disk disease,
the spine undergoes a downhill cascade of events: Biochemical changes
cause the disk to shrink, allowing the
vertebrae to slip out of alignment,
which can tear or rupture disks and
pinch nerves. The result is excruciating back and leg pain.
The current treatment for this often
debilitating back condition is a procedure called spinal fusion. The worn-out
disk is removed and a piece of bone is
grafted between the vertebrae above
and below it. In the new experimental
procedure, instead of fusing the vertebrae, surgeons insert an artificial disk
between them, a device made of two
metal plates connected by a moving
joint. Of the approximately half a million fusion patients in the U.S. each
year, Dr. Errico estimates that a third of
them could benefit more from disk
replacement than fusion.
The artificial disk allows the affected
part of the spine to bend normally.
When vertebrae are fused, they cannot
move, which forces the rest of the spine
to take up more of the burden of bending and flexing. As a result, as many as
30 percent of fusion patients will suffer degeneration of one or more additional disks within a decade after
surgery. By maintaining movement in
the affected area, artificial disks may
prevent further degeneration.
Several brands of artificial disks
have been in clinical trials, and one
received Food and Drug Administration (FDA) approval in October 2004.
Most of these artificial disks, including
the FDA-approved model and the one
that has been in trials at HJD, contain
both metal and plastic parts. But plastic wears out over time, a fact that concerns some orthopaedic experts. Since
most patients requiring disk replacement are relatively young, the ideal
material is one that is more durable.
Dr. Errico recently helped to
develop a disk, called Flexicore, made
entirely of a metal alloy called cobalt
chrome. “That’s the material they use
on the tips of bunker buster missiles,”
says Dr. Errico. “We’ve tested Flexicore
to the equivalent of 60 years of life, and
there’s no visible wear.”
The Flexicore disk is currently in
two clinical trials—one in the U.S. at
22 institutions, and one in Europe. Dr.
Errico is the principal investigator overseeing the U.S. trial. He is also helping
to develop an artificial disk for the cervical spine. Called Cervicore, this new
disk may undergo clinical trials beginning in early 2005.
The artificial disk replacements have
had encouraging early results. One of
the Flexicore clinical trial patients is
an avid figure skater who had been
unable to do any advanced moves for
several years because of lower back
pain. “Three weeks after surgery,” says
Dr. Errico, “she was out on the ice doing
turns and spins.” ■
— By Fenella Saunders
photography courtesy of stryker corp.
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