Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6011_Библиотеки_им_академика_М_И_Перельмана.pdf
C H A P T E R 6 6 Economics of Spine Care
445
In analyzing surgery for cervical spine disease, Patil et al found that the
number of procedures doubled in the years from 1990 to 2000.
14
During
that time, the patient age and number of comorbidities increased; however,
mortality and length of hospital stay decreased. Inflation-adjusted costs of
cervical surgery increased 48% during the decade, to surpass $2 billion.
The many recent and emerging advances in spine care contribute to this
being a very exciting time for spine care providers. Alternatives to spinal
fusion using the patient’s own iliac crest for graft material have been realized
in the form of BMP and other fusion materials. Even more exciting has
been the development of total disc replacements for the lumbar and cervical
spine. Designs of dynamic stabilization devices are numerous. Total facet
replacements are being evaluated. The arena of minimally invasive spine surgery is growing rapidly. However, who pays for all of these advances? Which
patients are most likely to benefit from expensive treatment options and
which can achieve good results with less expensive interventions?
The costs related to back pain were reported to range between $100 and
$200 billion a year in the United States.
15
Much of this cost was due to
patients missing work. The same authors reported that, annually, less than
5% of patients use 75% of the total cost of back pain. Another high cost
area for back pain is surgical implants. This was reported to be $2.5 billion
in 2003.
One component of back pain costs that is not often addressed is the cost
related to time off work. Ekman et al reported that costs related to loss of
productivity were about 84% of the total societal costs of back pain.
16
These
data suggest that one means of reducing the overall costs of back pain is
incorporating strategies to keep back pain patients at work as long as possible and to return them to work as soon as possible after back pain–related
absence.
Osteoporosis
Osteoporosis is a major concomitant factor in aging patients with back pain.
It is estimated that 55% of Americans, or 44 million persons, who are at
least 50 years of age have either osteoporosis or osteopenia.
17
The costs
related to this disease were estimated to be $19 billion in 2005, and were
expected to rise to $25.3 billion by 2025. Although not all of these costs can
be attributed to spinal fractures in the elderly, these account for a significant
part of the costs in the osteoporotic population. In addition, new fixation
techniques designed to be employed in the elderly spine with osteoporosis
are being developed.
COMPENSATION
With the government’s emphasis on cost reduction, rising costs need to be
addressed. Part of cost-cutting to date has included decreasing compensation to surgeons. Data over the last 10 years show that hospital income has
increased 18%, spinal device companies’ income has increased 154%, while
the spine surgeon’s payment has decreased 30%. However, there not only
needs to be more appropriate dollar reconciliation of the entities, but plaintiff attorneys’ involvement in the system and malpractice settlements need to
be addressed, as well as the whole adjudication process. In addition, insurance companies need to redesign products to help reduce costs and make
portability possible or a one-payer government system will evolve.
the need to pay malpractice and similar insurances by physicians, clinics,
hospitals, and manufacturers does not exist. This also contributes significantly to the ability to charge less for medical care.
COST-EFFECTIVENESS
While the concept of assessing treatments based on cost-effectiveness certainly has merit and appears to be relatively straightforward, such studies
are extremely difficult to perform in the United States, due to HIPAA and
the lack of any comprehensive data-capture system to assess all costs, not
just the hospitalization costs related to a single surgical event. There is no
way for researchers to have access to complete patient records. A surgeon
can access the costs incurred at his/her center and possibly the operative
costs at the hospital where the surgery was performed. However, one cannot get access to costs related to treatment provided outside of these entities. Such costs would be any services provided off-campus such as physical
therapy, chiropractic, medication, pain management, and in some cases,
reoperation. In addition, care providers do not have access to the indirect
costs such as disability payments made to a patient due to their back pain.
All these are important in determining the true cost-effectiveness of an
intervention. These difficulties, coupled with the wide variety of procedures
and implants used, make detailed cost analysis very difficult. If such studies
are performed, they will likely be criticized by those who disagree with the
results due to all of the potential problems with getting reliable full datasets
for patients.
There have been a few cost-effectiveness studies performed for spinal
surgery. From the SPORT (Spine Patient Outcomes Research Trial) study,
the cost-effectiveness of decompression and decompression with fusion were
compared to nonoperative treatment for lumbar spinal stenosis.
the cost per quality-adjusted life-year (QALY) over a 2-year follow-up, the
authors reported that the economic value of spinal surgery for this group
compares favorably with other health-related interventions.
Considering the rapidly expanding number of treatment options and
additional items that may be used, the cost-effectiveness calculation becomes
even more complicated. For example, consider the cost-effectiveness of anterior lumbar fusion. The simplest procedure may use a femoral ring allograft
and a graft extender. The cost of this simple procedure is greatly reduced
compared to cages packed with BMP, use of an anterior plate, and the use
of interoperative neural monitoring. Can it be shown that any or all of the
additional costs associated with the latter procedure result in a proportionally better outcome? To date, there are too few outcome data available to
address questions such as these, but they are relevant to the tune of several
thousand dollars difference in the cost of a single-level ALIF. Unfortunately,
while there may be sound biomechanical or litigious reasons for many of
the implants used in spine surgery, there are currently no clinical data available to demonstrate the benefits of many such interventions. As with many
things, the key likely does not lie in a simplistic dichotomy, either beneficial
or not beneficial. The real answer more likely lies in the need to determine
which combinations of implants and services are needed in which subgroups
of patients. Those with multiple risk factors for failures or with unusually
shaped anatomy may merit the use of more expensive constructs, while such
costs cannot be justified in simple cases.
18
Based on
MEDICAL TOURISM
One issue that has arisen in recent years is medical tourism. There are many
web pages that offer highly discounted medical services with the added
allure of foreign travel. While some patients feel that this may be their only
option for some expensive procedures for which they do not have insurance
or for which their insurance denies coverage, it is a system that has yet to
be fully tested. Many questions arise, such as how can they be assured that
they are traveling to a quality facility? Will patients receive quality implants
including tissue transplanted from others? What happens if a complication
arises? What if the patient dies overseas? How will complications that arise
after return to the United States be treated and paid for? Also of concern is
can America compete fairly in this arena? In many countries offering medical tourism packages, the cost of health care delivery is heavily subsidized by
the government, which helps drive the cost down. Also, in those countries,
WHERE TO GO FROM HERE
As previously mentioned, there is a movement going on in general to shift
from the current practice of medicine to one employing evidence-based
guidelines and cost-effectiveness to determine care. While this approach
appears logical, there are several potential shortcomings. These include lack
of rigorous research, inability to collect comprehensive cost data, and decisions made by bureaucrats in Washington without appropriate input from
physicians or patients.
Care providers have been reluctant to embrace treatment based solely
on evidence-based– and cost-effectiveness–based information. It is essential
to allow doctors the freedom to use their education and experience gained
from many years of practice. However, just as with residency training,
accountability with, perhaps, peer review might prove efficacious. The allimportant relationship of physician with industry needs clarification with
appropriate compensation. No one wishes for businessmen or engineers to
446
P A R T V I I I The Future of the Aging Spine
design new implants in isolation. In no other field other than those receiving
bailout support has any professional organization agreed with a government
or Advamed mandate as to hourly consulting fees. If this is to be accepted in
medicine, the authors suggest that a cap be applied to apply to Wall Street
executives, lawyers, accountants, etc.
In closing, no doubt there are changes on the horizon in spine medicine.
If health care is allowed to expand undeterred, our country will be bankrupt.
Hard decisions need to be made. It is in our common interest to involve all
factions, which must include patients and doctors, with transparency and
full disclosure as to the goals and consequences of various scenarios.
References
1. S. Keehan, A. Sisko, C. Truffer, et al., Health spending projections through 2017: the baby-
boom generation is coming to Medicare, Health Affairs 27 (2008) w145–w155.
2. National Center for Health Statistics: Health, United States, 2008, Hyattsville, MD, 2009.
3. Centers for Disease Control: Early release of selected estimates based on data from the 2007
national health interview survey, June, 2008.
4. Employee health benefits: 2008 annual survey. In: The Henry J. Kaiser Family Foundation
1-8, 2008.
5. R.D. Guyer, The paradox in medicine today: exciting technology and economic challenges,
Spine J. 8 (2008) 279–285.
6. K. Singh, A.R. Vaccaro, T.J. Albert, Assessing the potential impact of total disc arthroplasty
on surgeon practice patterns in North America, Spine J. 4 (2004) 195S–201S.
7. I.H. Lieberman, Disc bulge bubble: spine economics 101, Spine J. 4 (2004) 609–613.
8. D.W. Polly, S.D. Glassman, J.D. Schwender, et al., SF-36 PCS benefit-cost ratio of lumbar
fusion comparison to other surgical interventions: a thought experiment, Spine 32 (2007)
S20–26.
9. S.J. Ackerman, M.S. Mafilios, D.W. Polly, Economic evaluation of bone morphogenetic
protein versus autogenous iliac crest bone graft in single-level anterior lumbar fusion: an
evidence-based modeling approach, Spine 27 (2002) S94–99.
10. R .D. Guyer, S.G. Tromanhauser, J.J. Regan, An economic model of one-level lumbar arthroplasty versus fusion, Spine J. 7 (2007) 558–562.
11. V.V. Patel, S. Estes, E.M. Lindley, E. Burger, Lumbar spinal fusion versus anterior lumbar disc
replacement: the financial implications, J. Spinal Disord. Tech. 21 (2008) 473–476.
12. D.A. Levin, J.A. Bendo, M. Quirno, et al., Comparative charge analysis of one- and twolevel lumbar total disc arthroplasty versus circumferential lumbar fusion, Spine 32 (2007)
2905–2909.
13. E. Schluessmann, P. Diel, E. Aghayev, et al., SWISSspine: a nationwide registry for health
technology assessment of lumbar disc prostheses, Eur. Spine J. 2009.
14. P.G. Patil, D.A. Turner, R. Pietrobon, National trends in surgical procedures for degenerative
cervical spine disease: 1990-2000, Neurosurgery 57 (2005) 753–758.
15. J.N. Katz, Lumbar disc disorders and low-back pain: socioeconomic factors and consequences, J. Bone Joint Surg. Am. 88 (Suppl. 2) (2006) 21–24.
16. M. Ekman, O. Johnell, L. Lidgren, The economic cost of low back pain in Sweden in 2001,
Acta Orthop. 76 (2005) 275–284.
17. National Osteoporosis Foundation: Fast facts, http://www.nof.org/osteoporosis/disease
facts.htm. Accessed February 17, 2010.
18. A.N. Tosteson, J.S. Skinner, T.D. Tosteson, et al., The cost effectiveness of surgical versus
nonoperative treatment for lumbar disc herniation over two years: evidence from the Spine
Patient Outcomes Research Trial (SPORT), Spine 33 (2008) 2108–2115.
Micro- and Nanotechnology
and the Aging Spine
Lisa A. Ferrara
67
INTRODUCTION
In the United States by the year 2000, approximately 20% of all Americans
were older than 65. Twelve percent were older than 85. With an aging population, a higher proportion of the elderly seek orthopedic treatment, due
to the prevalence of musculoskeletal complaints. Currently, 25% of orthopedic patients are 65 and older. The Census Bureau projects that the 65
and older population will double from 33 million to 65 million by 2030,
while the younger age groups will remain the same. Physicians will be faced
with a greater number of individuals who are experiencing intellectual failure, immobility, instability, incontinence, insomnia, degenerative musculoskeletal disorders, and iatrogenic problems.
The aging process presents a cascade of events that affect the health of
the musculoskeletal system, in particular, the human spine. The maximum
bone mineral density of an individual is reached between the ages of 18
to 20 years of age. As aging progresses, muscle size and strength begin to
decrease, by as early as age 25. Accompanying these changes are reductions
in hormone levels for both men and women, contributing to a decline in
bone density and muscular strength. As we age, the musculoskeletal system
experiences degenerative changes resulting in fibrosis, stiffening, and shrinkage of the soft tissue; bone loss; joint changes; and tissue desiccation due to a
reduction in proteoglycans and a change in collagen type (i.e., intervertebral
10
disc).
With respect to the aging spine, this fibrosis and stiffening reduces
the osmotic properties of the disc and the ability of the disc to obtain and/
or maintain vital nutrients while eliminating noxious wastes. Disc desiccation initiates a cascade of progressive degenerative events leading to loss of
disc height, degenerative facets, and compression of the neural structures
resulting in pain. The degenerative process continues as the discs of the spine
undergo these arthritic bony changes, resulting in altered loading patterns
on the spine, further enhancing the patient’s pain and neurological deficits.
As a result, the elder population suffers from a variety of degenerative
disorders afflicting the spine, such as osteoporosis, degenerative disc disease,
compromised facet joints, spondylotic myelopathies, and stenosis, all resulting in pain and loss of motion. However, the longer life expectancies and
increased levels of activity at a much later stage in life place greater demands
on the spine and musculoskeletal system. Over the last decade, there has
been a surge in orthopedic implant development and spinal arthroplasty
devices to preserve or restore long-term joint motion.
As the overall life expectancy continues to increase worldwide, the need
for improved medical care increases and is expected to continue as the baby
boom generation crosses into the senior phase of their lives. With continued
development of novel medical technologies and a changing health care environment, microinvasive technological advancements in medicine continue to
progress, especially within the orthopedic and neurosurgical arena, where a
new generation of medicine is evolving.
Smart technology or “smart systems” are terms used to define systems
that are capable of imitating human intelligence. A smart system with respect
to medical devices is a system that can automatically sense and respond to
a changing environment once implanted into the human body. Smart technologies employ smart microsensors that can sense minuscule changes in
pH, chemistry, stress, strain, pressures, and temperatures; smart materials
that change their properties in response to a particular stimulus; microelectromechanical technologies that can sense and respond at the cellular level;
and nanoelectromechanical technologies that behave at the molecular level.
With respect to the aging spine, the ability to sense adverse changes in
vivo and manipulate cells and molecules presents the possibility of promising treatments for debilitating diseases and musculoskeletal disorders.
Smart materials that have the ability to repair and reorganize human tissue
and eventually allow for an engineered material and scaffold to be substituted by newly regenerated tissue provide an attractive solution for implant
and tissue longevity. Such novel materials should be capable of nonlinear
responses to imitate the mechanics of living tissue. Smart biosensors and
tooling can lend to improved surgical techniques and patient outcomes.
The incorporation of micro- or nanotechnology into spinal implants and
surgical tooling can enhance surgical accuracy; provide precision cutting
techniques for microsurgery with minuscule tissue damage; manipulate
cellular and subcellular structures; develop genetic engineering clinical
strategies; monitor and respond to tissue-targeting feedback; and create
biosensors that can provide the surgeon with real-time, continuous biofeedback with respect to implant performance during the lifespan of the applied
treatment. Smart materials with preprogrammed porosities can function as
biological sieves for implantable drug delivery systems, controlled differentiated tissue growth, and disease barriers. Finally, ultra-small tweezers that
are of nanosize allow for manipulation of molecules to change the course
of a disease.
The areas in which such interventions may become clinically applicable
in the aging spine include nuclear regeneration and replacement technologies, neural regeneration, localized delivery of pharmaceuticals such as bone
morphogenetic proteins for localized and controlled bone growth, delivery
of antibiotics and pain medications for long-term steady-state delivery,
and monitoring of implant lifespan. Nucleus regeneration may involve
the employment of semipermeable membranes that allow specific cells or
humoral agents to pass into a disc space that spur and nurture the regeneration process. Neural regeneration techniques must not only overcome the
humoral stimulation barriers required to induce regeneration, they must
overcome physical barriers and the complexity of the nervous system involving complex synaptic connections that are poorly understood. MEMS/
NEMS and polymer technologies can be utilized to create textured surfaces
that facilitate neural growth, while grids and tubes that can be electrically
stimulated can be used for orienting neuronal growth.
SPINAL ETIOLOGIES
12,13,21
Degenerative Disc and Congenital Disorders
The normal aging process results in degenerative disorders due to normal wear and tear of the joints and soft tissues. Although the process of
aging results in disc desiccation, facet degeneration, osteophyte formation,
and a cascade of mechanical and chemical events that lead to degenerative
447
448
P A R T V I I I The Future of the Aging Spine
conditions that cause pain and neurological changes, the ability of the body
to heal the tissues still occurs, although at a slower rate with progressive
aging.
Arthritis affects approximately 80% of people over the age of 55 in the
United States.
1,12
It is often triggered by injury, a weakened immune system,
and/or hereditary factors. Symptoms include inflammation, joint pain, and
progressive deterioration of joint surfaces over time which may result in anatomical changes of the joint surface, and edema inside the joint accompanied
by tissue debris. This condition demonstrates mechanical instability in the
joint related to the wearing away of the cartilage that is responsible for friction-free motion of the joint. The debris causes an inflammatory response
that can induce bone overgrowth and osteophyte formation that eventually
interferes with joint mobility. Rheumatoid arthritis is a progressive form of
arthritis that can be painfully destructive and may cause the interior joint
tissues to swell and thicken, resulting in joint disintegration and eventual
significant deformity.
Osteophytes or bone spurs are visible indications of a changing mechanical environment and are often found in areas affected by arthritis such as
the disc or joint spaces where cartilage has deteriorated. The formation of
osteophytes is the body’s attempt to halt the motion of the arthritic joint
and deal with the degenerative process, but often causes impingement on
the surrounding nerve roots.
Ankylosing spondylitis is a chronic hereitable disease characterized by
progressive inflammation of the spine with early sacroiliac joint involvement, followed by hardening of the anulus fibrosus and surrounding
connective tissue and arthritic changes in the facet joints.
5;6
The disease
eventually results in a loss of segmental mobility and “stiffening” of the spinal tissues.
Spinal Stenosis
Spinal stenosis is a disorder causing narrowing of the spinal canal or the
neuroforamen through which nerves exit the spinal column, thereby placing
pressure on the spinal cord. It occurs in all areas of the spine, however, most
often in the lumbar and cervical areas. Lumbar spinal stenosis-related symptoms include pain, weakness, or numbness in the legs, calves, or buttocks,
and are exacerbated when walking short distances and reduced when sitting, bending forward, or lying down. Cervical spinal stenosis demonstrates
similar symptoms in the shoulders, arms, and legs, in addition to fine motor
skill and balance disturbances. Treatment for spinal stenosis includes drug
therapy such as nonsteroidal antiinflammatory drugs to reduce swelling and
pain, and analgesics to relieve pain. Further conservative approaches to pain
involve corticosteroid injections (epidural steroids) to reduce swelling and
treat acute pain. Certain medical conditions may confound the diagnosis
and affect treatment choices. Diabetes-related peripheral vascular disease
and diabetic neuropathy or polyradiculopathy may superficially mimic the
neurogenic claudication of spinal stenosis, causing pain and neurological
deficits to the patient.
Osteoporosis
Osteoporosis is defined as the loss of bone mass and density due to a loss
of calcium exchange, which significantly compromises the strength of the
vertebral body.
1
It is often detected during the later stages of bone loss and
will weaken the mechanical integrity of the spinal column. Deformities may
develop as the vertebral segments lose a great deal of the cancellous structure, and eventually lead to compression and crush fracture resulting in a
kyphotic posture. Loss of bone strength may cause spontaneous fractures to
occur, in which the patient’s own body weight alone may cause vertebrae to
collapse leading to compressed nerves.
Spinal Deformity (Scoliosis, Kyphosis)
Scoliosis, kyphosis, and sagittal imbalance are spinal deformities that are
degenerative in nature in the older spine. Scoliosis is a three-dimensional
deformity that affects the coronal, sagittal, and axial planes. Kyphosis causes
sagittal imbalance and is identified as a degenerative curvature that affects
the sagittal plane. Lumbar deformities can be classified as idiopathic with
superimposed degenerative changes and de novo degenerative scoliosis, in
which the deformity starts at age 40 or greater, resulting from osteoporosis
and/or age-related degenerative disc changes. These deformities are characterized by the location of their curvatures (i.e., thoracic, lumbar, or thoracolumbar) and can be biplanar in nature. Treatment for such pathology
often results in a fusion with rigid instrumentation for curvature correction.
Currently, trapezoidal mesh cages with bone morphogenic protein (BMP)
are used to provide the anterior column support and improved curve correction with BMP to ensure fusion incorporation. However, this is a surgicallyinvasive approach requiring significant rigid stabilization implants, and is
subject to early failure if the surrounding bone integrity is suboptimal or
compromised, as that of the older spine.
Spinal Tumors
These are rare in occurrence. The physician is interested in determining the
cause of the tumor, whether there is a past history of cancer, and relieving
associated pain. If the patient’s primary condition is breast or lung cancer, it
is possible for the cancer to metastasize to the spine. Tumors can occur in
anyone without a history of disease. Fortunately not all spinal tumors are
malignant.
The foregoing are just a few of the spinal etiologies that can be associated
with the aging spine. Currently, there are conservative and surgical treatment options for these disorders. However, the conservative treatments do
not address the individual’s long-term pain and well-being, while the surgical options provide immediate treatment and address the pathology, but are
much more invasive and short-lived with respect to the patient’s lifespan and
quality of life.
NANOMEDICINE AND THE AGING SPINE
Bionanotechnology is the merging of biology with nanotechnology (performs at the molecular level) by incorporating fabricated nanostructured
materials and electronics into a living biological environment with functions
that will diagnose and respond therapeutically. This term also applies to
biomicrotechnology, which incorporates microstructured materials (performs at the cellular level) and electronics into a living environment. The
application of these technologies in a clinical environment has been termed
nanomedicine. Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) are microsized systems capable of performing biological tasks at the cellular or molecular level and are deemed “smart
technologies.” The specific application of micro or nanobiotechnology to
develop micro/nanosized medical devices will revolutionize medicine with
the potential to regenerate tissue, restore mobility, and increase the longevity of spinal implantation, as well as improve the quality of life and activity
levels for the aging population.
Drug Delivery Therapies
Over the last few decades, considerable advances have been made toward
drug delivery technologies. However, considerable challenges still exist. The
continuous release of therapeutic agents over extended time periods following a preprogrammed temporal profile, local delivery of the drug at a constant rate to the diseased microenvironment to overcome systemic toxicity,
improved ease of administration, increased patient compliance, minimized
risk of side effects, reduced hospital stay, and independent application all
pose significant challenges to the effectiveness of the delivered pharmaceutical. Injected or ingested drugs follow first-order kinetics with high blood
levels of the drug immediately after initial dosing, followed by an exponential decay in blood concentration. The rapid rise in the drug can lead to
toxicity, and the efficacy of the drug is diminished as the drug levels fall
exponentially. A continuous drug release profile in a controlled manner for
maintaining blood levels is an optimal release design. Currently, most controlled drug delivery systems are transdermal and subcutaneous in nature,
with current research, focused on the development of implantable systems
that will deliver therapeutic agents in a steady state manner, well underway.
The treatment of certain diseases such as osteoporosis and arthritis that
require the chronic administration of drugs could benefit from the presence
of implantable devices. These devices have the capabilities to provide localized continuous delivery to the physiological site. The benefits of implantable
7,19
C H A P T E R 6 7 Micro and Nanotechnology and the Aging Spine
449
drug delivery systems include the reduction of side effects with improved
feedback in a manner that mimics the physiological release profiles of the
immune system.
Micro and nanoengineered delivery devices have the potential to improve
drug delivery. Numerous materials that were once injected are now capable
of being inhaled or swallowed through novel nanodelivery devices, thus
improving patient compliance. However, the issues with fluctuating blood
levels and drug maintenance still exist. Therefore, a variety of microfabricated devices such as microparticles, microneedles, microchips, nanoporous
membranes, and micropumps have been employed in the development of
drug delivery systems for the goal of long-term implantation. In essence, this
is analogous to the behavior of the immune system. MEMS and NEMS
have provided an alternative to current means of drug delivery. The technology allows for systems to be employed that will ease application of the drug
and reduce the pain of delivery for injectable drugs. Microneedles of accurate, repeatable micron dimensions have been precisely designed in arrays
with reproducible lumen dimensions that pierce tissue allowing for delivery
of the drug in a localized manner, yet are small enough to avoid pain and
significant tissue damage (
Figure 67-1). Human nerves are insensitive to
micro- or nanoscale needles, making microneedle arrays for drug delivery
ideal for the elderly patient with fragile skin. Implantable nano-channeled
needles for drug delivery can provide improvement of control and optimization of pharmocodynamics, by maintaining prolonged steady state of the
drug performance and reducing the blood level fluctuation potential and
toxicity risks associated with conventional drug delivery. The drug release
rates can be accurately modeled and predicted due to the reproducibility of
the microneedles.
7
Eventually, these systems will be externally controlled by
telemetric means where a small drug delivery “chip” is implanted directly to
the diseased site and the chemical environment monitored and pharmaceutical agents delivered in response to a change in the chemistry, thus serving
both as a diagnostic tool and therapeutic agent for diseased tissue.
Nanopore technology has been implemented in the development of
microfabricated nanoporous membranes that are biologically, thermally,
chemically, and mechanically stable once implanted into tissue and are also
ideal for drug delivery systems and molecular sieves. These membranes are
ideal biological sieves that have uniform pore size and very low thickness,
making them ideally suited for drug delivery due to the ability of the membranes to have controlled diffusion and sustained release. The pore size, pore
length, and pore density can all be highly controlled and serve as ideal diffusion barriers. A drug reservoir can also be fitted to the device for sustained
delivery to the tissues.
7,19
Micro- and Nanoscale Smart Polymer Technologies
There are numerous types of smart polymers or polymers that exhibit a
sharp phase transition from hydrophilic to hydrophobic in response to
an environmental stimulus such as pH, temperature, pressure, or strain.
Numerous applications exist for these smart polymers or stimuli-responsive
polymers, such as drug delivery and drug targeting systems, biodetectors,
biosensors, and artificial muscles. Smart polymers are macromolecules capable of undergoing rapid, reversible phase transitions from a hydrophilic to
a hydrophobic phase and are thermodynamic systems that undergo a phase
transition for a certain range of parameters such as pressure, temperature,
8,15-18,20
and pH.
Furthermore, there are protein-based polymers that will
adhere to surrounding tissue or behave as a barrier to scar tissue, as well as
polymers that are electroactive in nature whose properties change drastically
upon change of stimulus. Additionally, polymers that respond differently to
changing mechanical properties such as strain rates have numerous potential
uses in the musculoskeletal system in terms of replacement devices or shock
absorbers in the human joints. Aging often results in degenerative joints that
have less efficient shock-absorbing behavior, which is further amplified in
the spine, where each intervertebral disc serves as a shock absorber to spinal
motion. Fast strain rates imposed on these types of polymers would elicit a
stiffening response, whereas slow strain rates would elicit a greater elastic
zone with greater deformation. Finally, the physical state of a smart polymer
coating on the surface of another material can switch from hydrophobic to
hydrophilic, where in the hydrophobic state, the surfaces have been found to
adhere to proteins and cells and can be patterned after human cells. In the
hydrophilic state, these proteins would be released. Such a technology can
be incorporated into applications toward engineering human tissue, such as
an intervertebral disc or cancellous bone and can provide adhesive or barrier
functions to the surrounding tissues.
Nanocoatings
With the advent of spine arthroplasty implants for motion preservation,
adherence of the implant to the surrounding bony interface is often challenging for long-term fixation. Biocompatible thermal spray coatings such as
titanium plasma sprays and hydroxyapatite coatings (HA) are the conventional means for improving an implant’s fixation to the surrounding bone
environment by promoting osseointegration at the interface. The HA coatings are generally 50 to 75 μm thick, and have a mean roughness of 7.5 to
9.5 μm, with a porosity of 1% to 10%, and a bond strength between 20
and 30 MPa. Titanium powders are generally sprayed and exhibit thickness of 350 μm to 600 μm, with a mean roughness of 30 μm and a porosity of 15% to 40%, with a bond strength of 25 MPa.
wide range in porosity and thickness can have limiting effects with respect
to osseointegration.
Nanocoatings or nanostructured thermal spray coatings exhibit
enhanced mechanical performance when compared to the conventional biomedical thermal spray coatings used on orthopedic implants, due to the uniformity and consistency in porous replication. Further characteristics such
as higher wear resistance, higher bond strength with the substrate, higher
resistance to delamination, higher toughness, and higher plasticity have
also been observed with nanostructured coatings.
been used extensively in the dental arena and tend to have a higher affinity
for osteoblast proliferation and uniform bone formation at the interfaces.
Improvement of these qualities using nanostructured technologies can lead
4,14,14
However, the
4,9
These structures have
F IG UR E 6 7- 1 Microscope image shows an array of hollow microneedles that are approximately 1000 microns tall next to a hypodermic needle typical of
those now used to inject drugs and vaccines. (Images from Google image, Microneedles. From Mark Prausnitz, Georgia Tech’s School of Chemical and Biomolecular
Engineering.)
450
P A R T V I I I The Future of the Aging Spine
to improved fixation of implants at the bone interface and the potential to
increase the implant’s lifespan within compromised or osteoporotic bone of
the aging spine.
Biosensors and Biochips
Although the exact pathomechanism by which a degenerative interverte-
bral disc leads to neural inflammation and pain has not been determined,
modern techniques of chemical analysis can be implemented to identify biochemical markers that participate in the degenerative cascade, and possibly
with the onset of pain. Clinical studies have shown that both the anulus
fibrosus and nucleus pulposus cells of the intervertebral disc express factors
such as neurotrophins NGF and BDNF that may influence and enhance
innervation and pain in the degenerated disc. Expression of such markers as
oncogenes Trk-A and Trk-B by the cells of the nondegenerated and degenerated disc suggests an autocrine role for neurotrophins in the regulation
of disc cell biology. Additionally, several cytokines have been implicated in
the process of IVD degeneration and herniation, with the investigations
predominantly focused on interleukin 1 (IL-1) and tumor necrosis factoralpha (TNF-α) as possible markers involved in the pathogenesis of IVD
degeneration.
Chemical markers are macromolecules present in the membranes and
fluids in the vicinity of the pathology. The ability to identify degenerative
markers could lead to treatment strategies that could diagnose early spinal
degeneration and provide treatments at an early stage, when the tissue is
capable of healing and reversal of the disease is possible. Microfabricated
biosensors can detect and target particular disease-related molecules and
proteins. The current methods for protein detection involve labeling procedures that are time-consuming; also, proteins must be in high concentrations for detection, at a point that may not be reversible with respect
to tissue healing. Implantable microsized biosensors provide a favorable
approach that allows for real-time analysis in minuscule dosages to shorten
the detection time and treatment options for the patient. Cantilever-based
biosensors for diagnostics have become a promising tool for detection of
biomolecular interactions with greater accuracy than conventional methods
(
Figure 67-2). A nanocantilever and/or microcantilever are devices that can
act as physical, chemical, or biological sensors by detecting changes in cantilever bending or vibrational frequency. It is the miniaturized counterpart of
a diving board that moves up and down at a regular interval, thus translating molecular or protein recognition into a mechanical motion, at either the
nano- or microscale. The mechanical motion can be detected by an optical
or piezoresistive readout detector system and, therefore, molecules adsorbed
on a microcantilever can cause vibrational frequency changes and deflection
of the microcantilever. Biomolecules that are immobilized on the surface of
the cantilever beam relay a surface stress to a readout system. If this surface
stress is disrupted by a variation in molecular mass or when a specific mass
of a molecule is adsorbed on its surface, such as that of a diseased molecule,
the readout will reflect the change and the diseased molecule can be detected
at a very early time point and at small manageable dosages for successful
treatment. Using a cantilever based on the detection of changes in vibrational frequency, the viscosity, density, and flow rate also can be measured
and monitored.
2
Biochips or Lab-on-a-chip (Figure 67-3)3 are microfluidic devices
that can conduct several laboratory functions and fluid analyses at rapid
speeds designed with microchannels smaller than a single cell, with large
surface-area-to-volume ratio where liquids follow a laminar flow pathway.
“Lab-on-a-chip” indicates generally the scaling of single or multiple lab processes down to chip-format. Conventional lab work conducted on patients’
blood samples are used to detect disease-related biochemical changes, and
often take as long as one to two weeks to obtain diagnostic results. The
biochip can conduct a continuous analysis on minuscule amounts of blood
within seconds in multiple iterations, and provide more than just a snapshot of information. In doing so, earlier detection of degenerative disease
is possible.
Early detection of diseased molecules can lead to earlier treatment of
the degenerative processes related to the aging spine, with the potential to
halt or reverse the progression of the disease. The degenerative cascade may
start with disc degeneration and desiccation, resulting in height loss, facet
hypertrophy, and the bony abnormalities that accompany the degenerative
cascade, including osteoporosis. If detected early, the cascade could be interrupted and the progression halted.
THE POTENTIAL FOR MICRO/NANOTECHNOLOGY IN THE AGING SPINE
The advancement of micro and nanotechnologies discussed in this section
presents novel opportunities for increasing the lifespan and improving the
quality of life for the aging population. Micro/nanomedicine has the potential to change the future of medicine and patient care. The areas of concentration for micro/nanomedicine are: (1) therapeutic delivery systems with
the potential to deliver gene and pharmaceutical targeting specific cellular
pathways, (2) development of novel biomaterials and tissue engineering to
guide tissue regeneration, and (3) biosensors and biochips for diagnostic
monitoring and therapeutic responses. For the aging patient with the degenerative spine, micro/nanomedicine provide the potential of reversing osteoporosis through nanomanipulation of molecules, gene therapy, localized
F IG UR E 6 7- 2 NEMS piezoresistive cantilever structures fabricated as cancer detection systems or to detect molecular changes in living tissue or fluids. The
right image shows actual multiplanar cantilever detection systems. (Left image from http://www.eurekalert.org/features/doe/2001-10/drnl-cm061802.phpen. Right
image from Li X, Yu H, Gan X, Xiaoyuan X, Pengcheng X, Jungang L, Liu M, and Yongxiang L: Integrated NEMS/MEMS resonant cantilevers for ultrasensitive biological
detection, ed 2 Journal of Sensors (637734): 1-9, 2009.)
C H A P T E R 6 7 Micro and Nanotechnology and the Aging Spine
F ig ur e 67 - 3 Example of the Lab-on-a-chip concept, in which blood
can be repeatedly sampled in minuscule amounts and the data accurately
transmitted remotely.
drug delivery, and the development of nano- and microscaffolds that are
osteoinductive and osteoconductive and can regenerate bone tissue. Biosensors and biochips will not only diagnose degenerative disorders of the spine,
but provide the possibility of treating degenerative etiologies detected early
in the cascade, to avoid the eventual fusion alternative, which has numerous
challenges in the compromised spine of the aging individual.
References
1. http://www.spineuniverse.com/displayarticle.php/article65.html. Accessed February 17,
2010.
2. http://www.azonano.com/details.asp?ArticleID=1927. Accessed February 17, 2010.
3. http://en.wikipedia.org/wiki/Lab-on-a-chip. Accessed February 17, 2010.
451
4. P. Bansal, N.P. Padture, A. Vasiliev, Improved interfacial mechanical properties of Al2O313wt% TiO2 Plasma-sprayed coatings derived from nanocrystalline powders, Acta Materialia. 51 (2003) 2959.
5. E. Benzel, L. Ferrara, S. Roy, et al., Biomaterials and implantable devices: discoveries in the
spine surgery arena, Clin. Neurosurg. 49 (2002) 209–225.
6. E. Benzel, L. Ferrara, S. Roy, A. Fleischman, Micromachines in spine surgery, Spine 15 (29)
(2004) 6–601.
7. T. Desai, S. Bhatia, Therapeutic micro/nano technology, Springer, 2006.
8. I.Y. Galaev, B. Mattiasson, ‘Smart’ polymers and what they could do in biotechnology and
medicine, Trends Biotechnol. 17 (1999) 335–340.
9. M. Gell, Development and implementation of plasma sprayed nanostructured ceramic coatings, Surface and Coatings Technology 48 (2001) 146–147.
10. B.H. Guiot, R.G. Fessler, Molecular biology of degenerative disc disease, Neurosurgery 47
(2000) 1034–1040.
11. X. Li, H. Yu, X. Gan, X. Xiaoyuan, X. Pengcheng, L. Jungang, M. Liu, L. Yongxiang, Inte-
grated NEMS/MEMS resonant cantilevers for ultrasensitive biological detection, J. Sensors
(637734) (2009) 1–9.
12. Millenium Research Group: US markets for spinal implants, 2006, 5413, 2006.
13. C.A. Niosi, T.R. Oxland, Degenerative mechanics of the lumbar spine, Spine J. 4 (202S)
(2004) 208S.
14. C.J. Oosterbos, A.I. Rahmy, A.J. Tonino, Hydroxyapatite coated hip prosthesis followed up
for 5 years, Int. Orthop. 25 (2001) 17–21.
15. N.A. Peppas, P. Bures, W. Leobandung, et al., Hydrogels in pharmaceutical formulations,
Eur. J. Pharm. Biopharm. 50 (2000) 27–46.
16. N.A. Peppas, K.B. Keys, M. Torres-Lugo, et al., Poly(ethylene glycol)-containing hydrogels in
drug delivery, J. Control. Release 62 (1999) 81–87.
17. N.A. Peppas, J.J. Sahlin, Hydrogels as mucoadhesive and bioadhesive materials: a review,
Biomaterials 17 (1996) 1553–1561.
18. N.A. Peppas, K.M. Wood, J.O. Blanchette, Hydrogels for oral delivery of therapeutic pro-
teins, Expert Opin. Biol. Ther. 4 (2004) 881–887.
19. D.E. Resiner, Bionanotechnology; global prospects, CRC Press, 2008.
20. K.E. Uhrich, S.M. Cannizzaro, R .S. Langer, et al., Polymeric systems for controlled drug
release, Chem. Rev. 99 (1999) 3181–3198.
21. A. White, M. Panjabi, Clinical biomechanics of the spine, ed 2. J.B. Lippincott Company,
Philadelphia, 1978.
Guided Lumbar Interbody Fusion
Ali Aragbi
68
k e y p o i n t s
Guided lumbar interbody fusion (GLIF) technique is a curvilinear minimally
invasive approach to the lateral spine, leveraging all adherent benefits of
lateral procedures with the patient in the prone position.
Allows for a circumferential fusion without repositioning the patient.
is minimizes procedural time and allows simultaneous access to
the posterior and anterior columns, enabling the surgeon to perform
circumferential releases prior to placement of structural anterior column
support.
Delivers a large implant with a large amount of bone graft directly across the
anterior column engaging the apophyseal rings for maximum support.
Allows for direct visualization through the ARC Portal System, via the
hinged lids, allowing the surgeon to easily confirm anatomy, to inspect disc
preparation and to ensure safe implantation of the interbody spacer.
Provides an alternative approach where other conventional access methods
may be difficult, to better accommodate patient pathologies.
INTRODUCTION
Interbody lumbar fusion techniques have become increasingly popular
because of improved rates of fusion, restoration of disc and foraminal height,
and promotion of lordosis.
spine lowers the incidence of pseudoarthrosis and recreates the patient’s
normal sagittal alignment.
posterior fixation techniques alone show a significant loss of disc height at
the injured segment and kyphotic deformation,
anterior column of the spine for interbody fusion. Conventional methods
for accessing the anterior spine use an anterior retroperitoneal approach
known as an anterior lumbar interbody fusion (ALIF), whereby a surgeon must mobilize the great vessels, sympathetic plexus, and ureter. This
approach is associated with considerable surgical trauma, and higher rates
of morbidity. As a result, most of these techniques typically require the presence of an experienced general or vascular surgeon, due to the risk of serious
complications.
Gaining popularity are techniques that access the anterior lumbar
spine from a lateral retroperitoneal approach with the patient positioned
in a lateral decubitus position. These procedures allow access to the anterior spine with little risk of injuring the peritoneum or great vessels, reducing the surgical risks compared to a standard ALIF operation. Since 1973,
similar retroperitoneal approaches were documented to access the lumbar
spine for performing lumbar sympathectomies and, starting in 1997 and
1998, Rosenthal et al. and McAfee et al., respectively, reported on minimally
invasive anterior retroperitoneal approaches to the spine for anterior lumbar
fusion. Early results show these alternative lateral approaches to the lumbar
spine to be safe and effective for anterior fusion of the first through the fifth
lumbar vertebrae.
The guided lumbar interbody fusion (GLIF) technique is a lateral
retroperitoneal approach whereby the lateral spine is accessed through
2
2
1
Accessing the anterior column of the lumbar
2
Late results of alleviating these effects through
3
necessitating access to the
452
a curvilinear portal with the patient in the prone position. Accessing the
lateral spine while maintaining the patient in a prone position offers many
advantages over similar lateral retroperitoneal approaches and conventional
ALIF techniques. First and foremost, this procedure allows the addition of
posterior fixation without having either to break the sterile field to rotate
the patient mid-surgery or to stage a series of surgeries. This reduces the
surgical time required for a full circumferential fusion procedure (otherwise
known as a 360), which directly relates to decreased anesthesia time and
costs for the patient, surgeon, and hospital.
INDICATIONS/CONTRAINDICATIONS
Surgical indications for spinal fusion include discogenic pain, segmental
spinal instability, progressive degenerative scoliosis, symptomatic spondylolisthesis, postsurgical pseudarthrosis, discitis, stenosis, degenerative disc
disease, and lumbar vertebral fractures that may be alleviated with a lateral
transpsoas approach.
Contraindications include systemic infection, osteoporosis, significant
comorbidities, degenerative spondylolisthesis grade 3 or higher, and bilateral
retroperitoneal scarring.
Additionally, the GLIF technique should be considered for revision
surgery on patients with significant scar tissue from previous anterior or
posterior approaches to the spine.
DESCRIPTION OF THE DEVICE
At the center of the GLIF technique is the ARC Portal System, a curvilin-
ear lighted retractor system with a hinged top (Figure 68-1). This instrument is delivered over sequential dilators to the disc space, and the hinged
top can be opened to gain direct visualization of key surgical landmarks
during disc preparation. The device has proximal and distal stabilization
capabilities to prevent portal migration during the procedure. In addition to the ARC Portal System, the GLIF technique utilizes specialized instrumentation to efficiently prepare the disc space for implant
delivery.
BACKGROUND OF SCIENTIFIC TESTING / CLINICAL OUTCOMES
Bergey and Regan report, in a study conducted on 28 patients between 1996
and 2003, that early results show the lateral endoscopic transpsoas approach
to the lumbar spine to be a safe, minimally invasive method for anterior
fusion of the first through the fifth lumbar vertebrae. Their study indicates
a risk of groin/thigh paresthesias and/or pain, but they report that these
symptoms have proven to be transient. Of the 28 cases, eight patients experienced the transient groin/thigh numbness and/or pain; six patients experienced a small peritoneal perforation due to blunt dissection, with no bowel
injuries; and two patients were converted to a mini-open lateral approach.
Their report concludes that “this approach can be successfully combined
with percutaneous pedicle screw fixation to provide a minimally invasive
approach for circumferential fusions.”
4
F IG UR E 6 8 - 1 The retracted ARC Portal System against a representa-
tive lumbar spine.
C H A P T E R 6 8 Guided Lumbar Interbody Fusion
F IG UR E 6 8- 2 The Calibrated Introducer delivering the Initial Dilator.
453
More recently, an extreme lateral interbody fusion technique (XLIF) has
been adopted, with positive results. Pimenta indicates, in a study conducted
to evaluate the XLIF technique for fixating lumbar degenerative scoliosis,
that the transpsoas lateral approach has lower morbidity, does not require
the use of endoscopes, avoids risks associated with anterior approaches, and
avoids the invasion of the posterior spinal canal. Analyzing a consecutive
series of 80 patients, Pimenta found the transpsoas approach to be a safe,
reproducible, minimally invasive technique able to reconstruct sagittal balance, correct degenerative scoliosis, avoid the potential risks to the anterior
approach, and promote rapid recovery.
5
Wright reports similar results in a study of his first 10 patients to
undergo the XLIF technique at Washington University. He reports the ability to perform a full discectomy, restore disc and foraminal height, as well as
to achieve indirect canal decompression from L1 to L5. There were no vascular, visceral, or neurological complications. Nine out of ten patients ambulated on the day of surgery and were discharged on postoperative day one.
One-year radiographic follow-up showed evidence of fusion. Additionally,
the study indicated minimal narcotic requirement. Complications included
three of 10 patients having transient pain with hip flexion that resolved by
6 weeks. His paper compared patients over 300 lb to those less than 300 lb,
and found the surgical corridor to remain essentially the same length with
no difference in outcomes, OR times, or blood loss. Hence, among one of
the advantages of this technique he cited was that it is particularly useful
in obese patients in whom anterior or posterior approaches would be more
6
difficult.
CLINICAL PRESENTATION AND EVALUATION
This technology is novel and is currently in the alpha phase of release. At
the time this chapter was published, only a few devices had been implanted
using this technique. There have been no surgical complications to date, and
follow-up data are presently being collected for better clinical evaluation.
OPERATIVE TECHNIQUE
Proper patient positioning and delivery of the initial dilator are integral to
the success of a GLIF technique. To facilitate proper trajectory of the instrumentation, the Calibrated Introducer was developed to repeatedly and reliably deliver the instruments to the surgical site (Figure 68-2).
The patient is positioned on the operating table in the prone position,
and lateral fluoroscopy is used to locate the proper operative level. The Calibrated Introducer is placed along the midline of the patient’s back, directly
above the operative level, and then secured with a Table Fixation Arm. The
Calibrated Introducer is adjusted to locate the posterior one third of the
operative disc space, which in turn identifies the axis of rotation for the curvilinear trajectory. Dilator 1 is attached to the Calibrated Introducer swing
arm (centered on the identified axis of rotation) and rotated until the distal
tip of Dilator 1 touches the patient’s skin. At this location, a 4 cm transverse
incision is made through the patient’s skin and fascia. A finger is used to
palpate through the subcutaneous tissue into the retroperitoneal space, and
can be used to sweep the peritoneum anteriorly and identify either the psoas
muscle or the anterior tops of the transverse processes.
Using the surgeon’s finger as a guide, Dilator 1 is advanced along the calibrated trajectory and delivered into the retroperitoneal space, through the
psoas muscle, and up to the annular wall of the desired location. Throughout
this step and the following sequential dilaution procedure, standard neuromonitoring technology can be utilized to ensure safe delivery of the dilators around the nervous structures. Proper dilator placement is confirmed
with lateral fluoroscopy, then anterior-posterior fluoroscopy. A guidewire is
delivered through the cannula of Dilator 1 into the vertebral disc and then
Dilator 1 is impacted into the intervertebral disc space, approximately 3 to
4 cm or to the midline. At this point, fluoroscopy can be used to verify final
placement of the initial dilator. The guidewire and Calibrated Introducer
can then be removed. Dilator 1 implanted into the intervertebral disc space
provides a fixed trajectory to the surgical site for the following access instrumentation.
Sequential dilation is performed using Dilator 2 and Dilator 3 to retract
the soft tissue through the retroperitoneal space and psoas muscle in preparation for the delivery of the access portal. The ARC Portal is delivered over
Dilator 3 and gently manipulated until the instrument is fully seated against
the lateral wall of the anterior spinal column (Figure 68-3). Throughout
the procedure, anterior-posterior fluoroscopy is used to confirm instrument
placement and trajectory. Final placement of the device is maintained using
a Table Fixation Arm. An Anterior Awl that retracts from the ARC Portal is
deployed into the intervertebral disc space to establish distal fixation to the
spine, and the dilators are removed.
The hinged top of the ARC Portal is then opened using a toeing wrench
to expose the operative site (Figure 68-4). Direct visualization is used to
identify local anatomy and prepare the operative corridor for the subsequent
disc-preparatory and implant insertion steps/operations. The distal perimeter of the ARC Portal can be explored using standard neuromonitoring
equipment. Penfield dissectors or elevators can be used to isolate and tuck
residual tissue behind the edges of the portal. Bipolar electrocautery can
also be used, if necessary, to further prepare for disc visualization. A Posterior Tang, which extends into the intervertebral disc space and attaches to
the ARC Portal, is assembled using the Posterior Tang Guide to complete
the protected working zone within the intervertebral disc space between the
Anterior Awl and Posterior Tang.
Specialized instrumentation is used to efficiently clean the disc space
through the ARC Portal. The lateral annulus and disc nucleus are removed
using an adapted annulotomy knife, annulus punch, and a series of curved
pituitary rongeurs. Specialized osteotomes, Cobb elevators, curettes and
rasps may be used to remove cartilaginous material from the endplates and
release the contralateral annulus. Alternatively the Rotating Actuator with
auxiliary Shaver Blades and Rotating Distractor attachments can be used to
454
P A R T V I I I The Future of the Aging Spine
clear the disc space (Figure 68-5). The Shaver Blade and Rotating Distractor attachments can be used as a guide to determine an appropriate Implant
Trial size used in the following step.
After the disc space has been sufficiently cleared, Implant Trials are used
to determine the appropriate size of the implant with respect to height and
foot print size. The GLIF system offers a range of footprint sizes: lengths,
heights, and lordotic angles. Anterior-posterior fluoroscopy is used to verify
placement of the Implant Trial. An implant is attached to the Impacting
Inserter, and the interior channels of the implant are filled with graft material. The Impacting Inserter and implant are delivered through the ARC
Portal into the disc space (Figure 68-6). Ideal implant placement is centered across the disc space, resting on both lateral edges of the disc on an
anterior-posterior projection. On a lateral view, the implant should ideally be
placed between the anterior third and middle of the disc space. Placement of
the implant is confirmed by both anterior-posterior fluoroscopy and lateral
fluoroscopy. The ARC Portal can be collapsed and all instruments are then
removed.
POSTOPERATIVE CARE
Radiographic follow-up until fusion has occurred is prudent. Postoperative
bracing is predicated on the patient’s bone quality, the degree of instability
present preoperatively, the choice of additional fixation, and intraoperative
variables, as well as surgeon choice.
COMPLICATIONS AND AVOIDANCE
The GLIF technique is a curvilinear access to the lumbar spine with the
patient in the prone position, affecting the anatomic areas between the following borders: the 12th rib and diaphragm in the cephalad direction; the
erector spinae, abdominal and oblique muscles posteriorly; the peritoneum,
aorta, and vena cava anteriorly; and the iliac crest in the caudal direction.
This window of anatomic landmarks confines the fascia, peritoneal fat, spinal plexus, and various traversing nerves. The following analysis reviews surgical techniques and anatomic precautionary areas that may be encountered
with the GLIF technique.
Dissecting from the skin to the retroperitoneal space should be
approached in a muscle-splitting approach. Mayer describes a blunt, musclesplitting approach in which each muscular layer (external oblique, internal
oblique, transverse abdominal muscles) is dissected in the direction of its
fiber orientation. Care is taken to preserve the iliohypogastric and ilioinguinal nerves, which occasionally cross the surgical field at the level of
L4-L5 between the layers of the internal oblique and transverse abdominal
7
muscles.
The major drawback in a lateral retroperitoneal approach is traversing
past the large psoas muscle, which covers the spine along its lateral aspect.
Additionally, the psoas muscle has various nerves bordering and traversing
through its confines, including the genitofemoral nerve and spinal plexus.
The psoas muscle acts as a stabilizer for the lumbar spine, like guy wires
F IG UR E 6 8- 3 The ARC Portal delivery over sequential dilators.
F IG UR E 6 8 -4 A retracted ARC Portal System, with inset view showing
an exposed annulus view down the ARC Portal.
F IG UR E 6 8- 5 The Rotating Actuator delivered through the ARC Por-
tal. The Proximal T-Handle is used to actuate the attached shaver bit, which is
delivered into the intervertebral disc space.
F IG UR E 6 8 -6 Delivery of an implant through the ARC Portal using the
Impacting Inserter.