Spine Surgery For The Next Millennium
Although back pain has been around since the beginning of human history, most of our understanding of
spinal problems developed only in the last 65 years, especially in the last three decades. Before the 1930's,
there was a scarcity of literature regarding spinal disease. In 1934, Mixter and Barr first described
herniation of the lumbar intervertebral disc and surgical treatment for this condition. In 1949, Verbiest
published the first article on spinal stenosis. Disc disease and spinal stenosis came to be known as the two
major causes of spinal disorders, yet spinal problems did not have the socioeconomic significance, as we see
today, until the 1950s
Posterior view of lumbar vertebral segment.
In the past three decades, great progress in the operative and nonoperative treatments of spinal disorders
has been made. Today, every advance in the diagnostic capability or surgical technique opens up new
possibilities for successful treatment. We now have improved spinal decompression and fusion techniques,
as well as bone grafts and bone substitutes. There are great varieties of instrumentation, including
segmental fixation devices, pedicle screw systems, fusion cages, as well as rods and plates. The new
fixation systems allow more adequate decompression of entrapped neural tissues without jeopardizing spinal
stability. As a result, we are now able to perform more aggressive surgical decompression, extensive bony
removal, corpectomy, radical tumor resection and correction of severe spinal deformities. With the superior
diagnostic studies available today, it is not necessary to "explore" the spine. In fact, there should be few
surprises during surgery. Every spine surgeon should have the exact surgical technique planned in advance.
Normal lumbar disc.
In spite of the tremendous strides made in science and technology, the diagnosis and treatment of spinal
disorders are still challenging. At this time, it appears that spine care is more and more influenced by
economic, political and sociological factors. For example, there are less resources and more constraints
imposed by managed care organizations. For the next several years at least, surgical trends will favor doing
less rather than more. There will be more emphasis on minimallyinvasive surgeries. The main intended
objective will be to reduce cost from the standpoint of the business interest. Hopefully, these less invasive
techniques will also reduce patient morbidity and mortality. In reality, many of the new surgical techniques
have not been analyzed rigorously in terms of outcome. These have to pass the test of time.
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The ball-bearing disc prosthesis. It failed due to loosening and expulsion.
In the year 2000 and beyond, there is no doubt technological progress will impact treatment of spinal
disorders. Information or computer technology, as well as imaging and other diagnostic techniques, will
have a significant influence. Advances in basic science will allow revolutionary application in diagnosis and
treatment of spinal problems. Particular attention should be paid to molecular biology. New discoveries are
being made of genes involving tumors, neurological, metabolic and degenerative spinal diseases. The new
knowledge will increase our ability to treat these conditions. Currently, genetic engineering techniques are
being used to produce substances which stimulate spinal fusions. Many bone growth factors have been
identified. One group of these factors is the bone morphogenic proteins (BMPs), which are lowmolecular
weight proteins, isolated from bone matrix, some of which are obtained through recombinant DNA
synthesis. These BMPs presumably stimulate local progenitor cells in tissues to enhance bone collagen
production. This initiates the bone formation necessary in spine fusions.
The multielastomeric disc replacement. It has a woven outer layer and a soft nucleus. Attachment to bone is
a problem.
In the future, there will be greater understanding of neurological function. This will allow us to modify "pain
experience" and provide relief through targeted therapies. This new knowledge can also be applied in more
effective electrophysiological techniques to be used in diagnosis and at the time of spinal surgery.
Thermoplastic elastomeric disc spacer. Three different durometers: nucleus, annulus, and endplates.
There will be more advanced imaging technologies, which will increase the sensitivity and specificity of
diagnosis. MRI, for example, will have better resolution and will be obtained in a shorter period of time, with
more patient comfort. The MRI machine will be smaller, but will be more "open," thus causing less
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claustrophobia in patients during the examination. The studies may be obtained with the patient in a sitting,
standing, prone or supine position, even when moving. There will be therapeutic MRI, which will allow
surgery with real time visualization. These advance 1 imaging technologies will enhance minimally invasive
spine surgical techniques.
Inflatable flexible disc prosthesis.
The minimally invasive procedures will be more developed as diagnostic tools and therapeutic approaches.
Percutaneous discectomy and fusion will be more effective. There will be more "userfriendly" endoscopic
instruments for spine procedures. Thoracoscopy, laparoscopy and retroperitoneoscopy will become less time
consuming with improved optics, electronics and engineering. Many of the instruments will be computer
aided, in fact, the computer and surgical technologies are converging, and are leading to more virtual reality
surgeries.
Disc prosthesis with metal plate, cushion, and anchoring screws between the plates is an elastomeric
cushion.
otally different therapeutic approaches may emerge and become more accepted for certain spinal disorders.
At this time, there is no satisfactory treatment for patients with multilevel painful degenerative spinal
disease. The problem becomes more compounded when the patients are overweight and Reconditioned. The
wide abdominal rectus plication surgery may be an answer for such patients. This is an actual back surgery
without touching the back itself.
Disc replacement with nested box and springs.
Severe spinal stenosis occurs in the elderly, many of whom also have other significant medical problems.
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For some of these patients, general anesthesia is a major risk. There will be minor surgical procedures which
will provide relief with minimal risk. This type of "unconventional" or "indirect" surgical approach may
become more popular in the future.
The sandwich disc prosthesis with porous metal plates and elastomer cushion.
Although we will continue to see newer techniques of spinal instrumentation and fusion, there will be a
general trend away from spinal fusions. Today, spinal arthrodesis provides satisfactory relief for many
patients; however, there are major problems for at least 30% of the patients over time. Some of the
problems include donor site pain, nonunion and failure of the metal fixation. Degeneration of adjacent
motion segments is a long term sequelae. Surgical complications, early and longterm problems tend to
increase with longer fusions. In general, patients who undergo spinal fusions for multilevel degenerative disc
disease tend to do poorly. Even after solid fusion, pain relief is less than expected or it does not last as long.
Instability and additional degeneration is accelerated at the adjacent levels, if there are already some
degenerative changes at the nonfused level. In view of these problems associated with spinal fusions, it is
therefore logical to develop a physiological disc replacement to preserve normal motion, disc height and
stability.
The disc prosthesis of hinged metal components with springs and screens.
A normal, natural intervertebral disc has a deceptively simple appearance with an outer annulus fibrosus
and an inner nucleus pulposus; however, it is extremely difficult to design an effective artificial disc
replacement. The basic requirements of a disc prosthesis include biocompatibility of the material, normal
disc geometry, kinematics, dynamics, motion constraints, endurance and good fixation to bone. In addition,
it must be failsafe. Let us consider only one of the basic requirements, endurance. Today, a typical spinal
fusion is performed on patients between the ages of 35 and 50; therefore, the life span of a disc
replacement should be at least 40 years. An average person experiences two million strides or one million
gait cycles in one year and 125,000 spinal flexion and extension movements per year. These add up to at
least 85 million spinal loading cycles in 40 years. Kostuik believes that the device and material should be
tested to a least 100 million cycles. This number is a factor of 6.5 more than the longest wear and fatigue
tests of any other orthopedic implant.
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The disc prosthesis with pinned metal plates separated by high-molecular-weight polyethylene ball.
There have been numerous attempts to develop an ideal disc replacement. One of the earliest attempts was
the ballbearing implant, which was used in a large number of patients. The disc space was often
hypermobile, and the patient developed more pain. After several months or years, many of the ball bearings
eroded into the vertebral bodies or displaced into the spinal canal and even into the abdominal cavity. There
were many other failed prosthesis, such as the nested boxform device, with springs inside which became
ineffective after scar tissue invasion. A number of "sandwich" implants were also designed with metal plates
and silicone or elastomeric cushions; however, major problems developed, and they had to be discontinued.
The disc prosthesis with metal plates pinned into the vertebral endplates. A silicone cushion is between the
plates.
At this time, the Kostuik device, with hinged metal components containing springs, is being studied. In this
prosthesis, fibrous tissue may grow into the springs and hinges, causing it to be less effective. One concern
with this type of articulating implant is the wear product. The body reacts to the volume of the wear
particles, as well as to the biological incompatibilities. The SB Charite disc and endoprosthesis probably has
the largest tract record. It was initially developed in East Germany and has been used in several hundred
patients so far. It has two metal end plates and a highdensity polyethylene center; however, the motion is
in the middle of the disc space, which is actually too anterior. The true physiological center of rotation is in
the posterior aspect of the disc space.
The disc prosthesis with nucleus replacement made of metal, hard plastic, or elastomers, allowing flexion
and extension movement.
Ray is using Hydrogel placed in a pair of doublewoven jackets to replace the nucleus only. This device swells
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and locks in position after it is inserted after discectomy through an endoscopic approach or by open
surgery.
The disc replacement folded before insertion. It is inserted into the enucleated disc space and unfolded.
A healthy, natural disc functions far superiorly to any manmade replacement available today. It is
reasonable to transplant a normal disc from a different level of the same patient or from another individual
or even a different species. Luk and Associates have performed disc autografting in monkeys. Others have
published experiments in dogs, using allografts for disc replacement. An intact disc with its adjacent
endplates or parts of the vertebral bodies is being transplanted as a unit. In dogs, the normal disc
mechanical properties were preserved for as long as 1.5 years, but all dog allografts eventually developed
loss of disc height and degenerative changes. The lack of diffusion of nutrition to the allografts may be the
problem. In monkey autografts, there was minimal evidence of gross degeneration for up to one year.
Although gradual loss of water content was noted, the nucleus pulposus reaccumulated proteoglycans after
an initial drop in the first four months. There was significant increase in the hydroxyproline content in the
annulus fibrosus and the nucleus pulposus. The study with monkey autografting showed that the
transplanted disc could survive a period of ischemia. Other researchers are planning the use of xenografts in
disc transplantation. Instead of the entire disc and endplate unit, only parts of the disc may be transplanted.
There are still major hurdles to overcome, including the lack of diffusion of nutrition, biocompatibility in
allografts and xenografts and other problems inherent in transplant surgery.
It is probably too early to predict the future of disc transplantation. Yet, we can look back to only 50 years
ago when no one predicted the possibility of heart and kidney transplantation.
In the next millennium, I believe that there will be developments in spine surgery which are unimaginable
today. We may learn to cure most spinal diseases and repair or replace parts of the spinal cord or even the
brain itself.
The paired double-woven disc prosthetic nuclei inserted after discectomy. The prosthesis swells after
insertion. There is hygroscopic gel inside semipermeable membrane.
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