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The future is bright
for new, improved methods of spinal surgery. Other technological and biological
advances are on the horizon that will work in concert with minimally invasive
techniques. Several of these, such as computer-assisted image-guided technology,
bio-resorbable, flexible and radiolucent spinal implants, and genetic-engineering
of disc tissue, bone fusion, vertebral bone, and other steps forward, are worthy
of discussion.
Spinal Navigation Technology
Conventional surgery of the spine often involves taking an x-ray during the
procedure to confirm the location of the spine or to confirm satisfactory placement
of spinal implants (e.g. screws, rods, hooks, plates). Often, surgeons use "live"
x-rays during surgery (called fluoroscopy, floor-ah-sko-pee) to obtain this
information.
In the past decade, great advances have been made that has taken navigation
of the spine (or localization) to a new height. Also known as "computer-assisted,
image-guidance," navigation technology is advancing at a rapid rate. More powerful
and elegant than simple x-ray technology, spinal navigation technology uses
a computer and radiographic studies (x-rays) of the patient to allow the surgeon
to know precisely where he/she is at all times.
Spinal navigation technology enables the surgeon to more accurately place spinal
instrumentation, perform decompression (e.g. eliminate pressure on nerves),
remove tumors, and other tasks. Three-dimensional models of a patient's own
spine appear on a computer screen with virtual representations of real surgical
instruments that the surgeons have in their hand. Surgeries can even be planned
'virtually' on the computer before a patient even goes to sleep under anesthesia.
For example, screw diameter, length, and other measurements can be made with
greater accuracy.
The future of spinal navigation is exciting. Rather than send a patient for
an preoperative CT or MRI scan, in the future surgeons will be able to obtain
images in the operating room that can instantly create computer models of the
patient's spine. These models can be used to help navigate the spine during
surgery. Intraoperative CT, MRI, and fluoroscopy-based CT offer great potential.
The end result is enabling the surgeon to visually "travel" in and out of a
patient's spine on computer, thereby allowing them to see things that the human
eye cannot during a typical surgery. As spinal navigation technology advances,
newer minimally invasive techniques will become available.
Future Biomaterials for Spinal Implants
Titanium
Great success has been achieved thus far using cages, rods, screws, hooks, wires,
plates, bolts, and other types of spinal implants made from stainless steel
and (more recently) titanium metal. The great advantage of titanium is that
it is allows for better CT and MRI imaging to be performed after implantation
with little interference. Stainless steel causes significant "blurring" of CT
and MRI images.
Bone Graft
Other types of materials used in spinal surgery include bone graft. Bone is
either harvested from the patient's own body (autologous bone) or bone from
a bone bank can be used. Bone bank bone (allograft) comes from cadavers and
is commercially processed for transplantation into patients. One problem is
bone taken from the patient's pelvic bone (ileum) can cause chronic pain; the
other is the supply of cadaver bone can be limited.
Bone Morphogenetic Proteins (BMP)
Molecular biological advances will tie in with these navigational and biomaterial
advances. Very soon, genetically-engineered proteins called Bone Morphogenetic
Proteins (BMP) will be commercially available for bone fusion surgery. This
will likely eliminate the need for either autologous or allograft bone use and
all of the potential morbidity and limitations inherent in these grafts. BMP
can be placed inside a collagen (protein) sponge or other ceramic-type implants
and used instead of bone in areas of desired fusion (e.g. disc space, backside
of the spine). Thus, in the future, we may be using biodegradable spacers or
"fusion carriers" that house BMP, allow for a solid fusion, and then dissolve
away themselves leaving only fusion bone behind.
Ceramic and Carbon Fiber
Other materials have been used as carriers of bone graft or vertebral body replacements
such as ceramic and carbon fiber. Carbon fiber is radiolucent, which means that
implants made of this material do not show up on x-ray. This has the advantage
of allowing the bone fusion to be better seen. Future developments will bring
even greater advances.
Plastics and Polymers
Because of the potential morbidity of using a patient's own bone (autologous
bone) and the limited supply of cadaveric bone, attention has been directed
to developing newer materials to serve as spacers and conduits for bone graft
material. Other forms of plastic are being developed such as polyether ketone
combinations that will be radiolucent yet provide strength and support.
Polylactic Acid (PLA) polymers are also being developed that can actually biodegrade
over time. In other words, the PLA will do its job in holding bone graft material
and providing support long enough for a fusion to take place, and then it slowly
dissolves (hydrolyzes) away after a year or so. Still other materials are being
developed that would allow some flexibility and dynamism in a spinal implant.
There is some agreement that certain spinal implants may be too rigid and more
natural, flexible substances may be a better substrate from which implants could
be made.
Disc Replacement or Disc Regeneration
In the future, disc replacement or regeneration may replace the role of fusion
in some patients. Though fusion will likely always be a very useful form of
treatment in many patients, there may be some patients that will benefit from
an implantable artificial mechanical disc. Several forms of artificial disc
implants have been used in Europe and are currently being tested in clinical
trials in the United States.
The theoretical advantage is that artificial disc replacement will result in
improved pain and function with maintenance of some motion at a disc space that
otherwise may have been fused solidly by more conventional techniques. Other
forms of disc replacement may involve re-establishing the inner nucleus of the
disc only with a gel-like material and utilizing the natural anular lining of
the disc to contain it (without a metallic component).
Equally as exciting is the possibility that genetically-engineered cells may
be surgically implanted or injected into a degenerated disc, allowing for regeneration
of disc material that can serve as a shock absorber like the disc we are all
born with. There is some experience already with the use of engineered cells
in reproducing knee cartilage, so the possibility of use in the spine is real.
Summary
Great advances in just the past decade have allowed physicians to treat spinal
disorders more effectively. Further advances in biomaterial development, computer-assisted
image-guided technology, molecular biology of bone and disc will all be integrated
together to develop very powerful techniques for treating spinal disorders.
It is this integration of emerging technology and biological advances that will
result in smaller incisions, less trauma to normal tissues, faster healing time,
equivalent or better relief from pain and neurological problems, and quicker
return to functional status.
This article is an excerpt from a book titled Save Your Aching Back and
Neck, A Patient's Guide (Second Edition, May 2002, completely revised).
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