The spine is a column that is made of up bones, discs
and ligaments. The blocks of bone (or vertebrae) provide the anterior
support and structure of the spine. The discs are in between the bones
and act like a “shock absorber” between the vertebrae. The discs also
contribute to the flexibility and mobility of the spinal column. The
discs are made up of two parts:
1) the
inner portion of the disc is a jelly-like material and is called the
nucleus pulposus and
2) the
outer part, called the annulus fibrosus of the disc, is stronger and more
fibrous. The anulus fibrosus surrounds and supports the inner jelly
material.
Disc material is mainly composed of water and other proteins. As a
normal part of aging, the water content gradually reduces. This can
cause the disc to flatten out and even develop tears or cracks
throughout the annulus fibrosus. These discs are often referred to as
“degenerative” discs and may or may not cause pain.
In the case of a degenerative disc, the inner jelly material (the
nucleus pulposus) can bulge out and press up against the annulus
fibrosus. This can stimulate the pain receptors causing pain to occur.
The cracks or tears that develop within the annulus fibrosus can also
become a source of pain. Finally, the inner nucleus can also come out
through the cracks in the annulus and compress nerves or spinal cord, a
condition that may cause weakness, pain, pins and needles or numbness,
and may require surgery.
Current Treatment Options for Prolapsed Discs
Non-surgical options for people with disc protrusions in the neck
include rest, heat, pain medications and physiotherapy. When
non-surgical treatment options fail, surgery is often the next step.
This usually means spinal fusion surgery. Neck pain with compression of
the nerves in the neck or spinal cord is a common condition that affects
the spine and may require surgery. If only nerves are compressed, with
symptoms in one arm, a period of conservative management is instituted
and if this fails surgery is contemplated. Early surgery is performed if
there is severe weakness or pain that cannot be effectively controlled
with available analgesia. If the spinal cord is being compressed,
surgery to decompress the spinal cord is usually recommended. This
compression can be caused by bulging disc or bony spurs.
Surgery on the spinal cord is performed either from the back of the
neck (laminectomy) or through the front of the neck (cervical discectomy
or vertebrectomy). If the compression of the spinal cord is from the
front, then the decompression must be done from the front (anterior
decompression). Typically if the entire disc is removed, a wedge of bone
is taken from the hip and put into its place, possibly with a plate and
screws to hold it into place (see below). This is commonly referred to
as an anterior cervical decompression and fusion.
(Above left): MRI scan of the cervical spine showing a typical disc
protrusion between the 5th and 6th cervical
vertebra compressing the spinal cord
(Above middle): A Schematic diagram of a typical anterior discectomy
and fusion procedure. A block of bone graft is placed into the space
left when the disc is removed
(Above right): A postoperative x-ray on the patient shown to the
left. The disc has been removed, a block of bone has fused the 5th
and 6th vertebrae and a plate with screws holds it into place
This
is a common operation and often no bone graft from
the hip is taken nowadays. Instead bone from a bone bank (donated
cadaver bone called allograft) or plastic cages filled with bone
substitutes are used. Whilst it takes pressure off the spinal cord,
it necessitates that at least 2 of 7 bones in the neck are fused. This
does reduce some of the movement in the neck, but patients typically do
not notice it unless several levels are fused. Typically after this
surgery, the patients were a neck brace for 6 weeks.
The problem with fusing bones in the neck are that adjacent levels in
the neck are placed under more strain. This has increased “wear and
tear” at the surrounding disc space levels has been termed “adjacent
segment stenosis”. We now know that if 10 people have a single level
fusion, at 10 years 3 have had to have another operation for narrowing
at the next level either above or below. Secondly, the bone does not
always heal or "fuse" correctly. In fact, the overall success rates for
these procedures range from 48% to 89%. Finally, 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 surgery.
Cervical Disc Replacement
Instead of Cervical Fusion
A new technique which has been
available throughout the world since 2001 is removing the disc and then
replacing it with an artificial disc. This has 2 main benefits:
1)
Motion is maintained and the patient will not feel a restriction in the
range of motion.
2)
Theoretically adjacent segment disease will not occur.
Consequently, patients undergoing decompression and placement of an
artificial cervical disc do not need a brace after surgery and may need
less surgeries on their neck in the future.
The
idea of spinal disc replacement is not new. It was first attempted 40
years ago when implanted stainless steel balls were implanted into 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. The Bryan cervical disc prosthesis
represents a state of the art disc prosthesis, although several are now
available. A newer prosthesis, termed Prestige LP
The
Bryan Cervical Disc System is a 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.
Expect US release in 2008
.
(Above)
X-rays of the cervical spine after implantation of an artificial disc.
Normal movement is preserved.
The
initial clinical experience with the Bryan Total Cervical Disc
Prosthesis has been promising.
(Above
left): The Bryan artificial disc prosthesis.
(Above
right): A skeletal model of the cervical spine showing how the
artificial disc is placed.
