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C H A P T E R 5 8 e Role for Biologics in the Aging Spine
385
(8 of the 50 patients) in this population. In fact, there were increased perioperative complications in the autograft group (23 of the 52 patients). These
complications included donor site infections, cardiac issues, pain, urinary tract
infections, and neurologic deficit. Additionally, they found that the rhBMP-2
group had significantly better fusion grades on radiographic imaging and equivalent improvements in health-related quality of life outcomes for both groups.
Though BMPs provide substantial benefits in spinal arthrodesis, their
use is not always without complication.
12
Potential complications include
the formation of ectopic bone, hematoma and seroma formation, bone
resorption and graft subsidence, antibody formation, and possible carcinogenicity. While some of the effects may be dose or carrier related, many of
the applications currently considered for their use are off-label and their use
has to be considered carefully. Further, the cost-to-benefit considerations
remain to be elucidated.
OTHER BONE GRAFT ALTERNATIVES
Many other potential bone graft materials have also been considered for use
alone or in combination with local bone to limit morbidity associated with
iliac crest autograft. Some of these alternatives include allograft, demineralized bone matrix (DBM), and synthetic materials such as ceramics.
While none of these bone graft alternatives possess all three factors necessary to promote osteogenesis, their utility in specific clinical situations is
being studied. No matter what substance is chosen, the local and systemic
environment must be hospitable to the formation of new bone, and there
must be adequate blood supply, mechanical stability, and a lack of growthinhibiting factors (e.g., nicotine, infection).
Allograft
Allograft bone provides an osteoconductive scaffold for new bone formation.
Various allograft bone types are available. Successful use of allograft bone
in spinal surgery is largely dependent on its placement. When structural
allograft is implanted in the anterior column, it is associated with relatively
high fusion rates, both in the cervical and the thoracolumbar regions of the
13,14
spine.
sion, as in the posterior spine, it incorporates at a slower rate than autograft
and leads to lower rates of arthrodesis when used alone.
However, when nonstructural allograft bone is placed under ten-
15,16
A recent study by Anderson and associates17 evaluated the use of morcelized femoral head allograft with and without instrumentation in the elderly.
The study did not harvest autograft from any of the patients. The demonstrated successful fusion, determined by radiographs, is 68% with allograft
alone and 81% with allograft plus instrumentation. Additionally, there were
15 of the 94 patients treated who required revision surgeries, a revision rate
that is similar to what is seen when using autograft alone. This study demonstrated superior outcomes with allograft plus instrumentation for posterolateral fusion surgeries. However, more importantly for this review, it is one
of the few studies to specifically evaluate allograft in an elderly population.
Demineralized Bone Matrix
Demineralized bone matrix is allograft bone that has been decalcified to
produce a product of collagen and noncollagenous proteins. Multiple products are available, but there are relatively limited data available regarding
their efficacy, as limited regulatory requirements have been established for
these minimally manipulated tissue products. Further, studies have questioned the osteoinductive nature of one product versus another, as well as
lot-to-lot variability.
There are few randomized controlled clinical trials evaluating the use of
DBMs in humans. In one series, 77 patients underwent one, two, or three
level noninstrumented anterior cervical discectomy and fusion procedures,
using freeze-dried structural allografts filled with a DBM or autogenous
iliac crest bone graft alone.
were 54% and 74% for the allograft/DBM and autograft groups, respectively. Despite this relatively easy fusion environment, inferior fusion rates
were observed in the experimental study arm.
In contrast, another study, involving 50 subjects who received lumbar
interbody fusions, reported a 96% success rate after implanting titanium
mesh cages packed with a DBM and a coralline hydroxyapatite carrier.
18,19
20
At a minimum of 1-year follow-up, fusion rates
21
The authors performed circumferential fusions with posterior instrumentation and autograft but they did not have a control group to compare against.
However, they only used the DBM anteriorly. Again, this study only used
the DMB in the anterior spinal column where fusion is generally more easily
achieved. This is an excellent example of how DBM could be used as a bone
graft extender by eliminating the need for iliac crest bone graft (ICBG) in
the anterior fusion construct.
Unfortunately, there are no studies specifically evaluating the use of
DBM in the elderly. However, given the highly variable composition and
ability to induce fusion between different DBM products, it is doubtful that
a definitive study could be adequately performed in an elderly population
that could be generalized across multiple DBM products or even across different production lots of the same product.
Synthetic Materials (Ceramics)
Synthetic materials are being considered with increased frequency as bone
graft materials. These provide an osteoconductive scaffolding and are generally used as bone graft extenders or supplements to local or iliac crest bone
graft. Again, because the regulatory pathways for approval of such products
are not as stringent as for other products, such as the BMPs, the studies are
generally less controlled and rigorous, making the efficacy of such products
more challenging to interpret.
One of the inherent disadvantages of ceramics is that they are relatively
weak and brittle. When ceramics are introduced into the anterior spinal
column they must be protected from the significant compressive forces by
internal fixation until the graft is incorporated into the new bone growth.
Like allograft, ceramics are also inferior to autogenous bone when placed
under tension.
22
Other biologically active materials, such as local autograft,
demineralized bone matrices (DBMs), or osteoinductive growth factors,
may be combined with ceramic osteoconductive matrices to form a composite graft that can then lead to increased amounts of bone formation.
Bone Marrow Aspirates
Autologous bone marrow represents another source of osteogenic cells and
osteoinductive proteins for spinal fusion. The most significant advantage of
this technique is that aspiration of bone marrow has much less morbidity
than the procurement of iliac crest autograft. However, it must be used in
combination with an osteoconductive matrix, bone marrow aspirate to form
a composite graft. The major limitation to this technique is that unfractionated bone marrow has only moderate osteogenic potential. Even in
healthy adults, it is estimated that only 1 out of every 50,000 nucleated bone
marrow cells is capable of undergoing differentiation into an osteoblast.
Additionally, it has been shown that the number of viable bone marrow
cells decreases significantly with age, which may limit utility in an elderly
population.
an instrumented posterolateral fusion study.
26
One recent study demonstrated comparable fusion rates to autograft in
27
Both allograft and DBM can
be combined with the osteogenic elements of bone marrow aspirate to help
promote fusion. By adding bone marrow aspirate, osteogenic elements may
be added to help promote fusion. Studies have shown improved fusion rates
with the use of bone marrow aspirate from iliac crest when used in conjunction with autologous autograft in a bone paucity model.
28
Recently, aspirates
from the vertebral bodies accessed during pedicle screw instrumentation
have been shown to be an excellent source of osteogenic cells with only modest depletion with serial aspirations.
29
However, there was a reduction in the
cellularity of the specimens in older individuals.
OTHER POTENTIAL APPLICATION OF BIOLOGICS IN THE AGING SPINE
Vertebral Body Augmentation in Vertebral Body Compression Fractures
Unique to elderly patients, vertebral compression fractures are the most
common type of osteoporotic fragility fracture that can occur from low
energy trauma, such as a fall from standing height or less. Although many
are asymptomatic, the possible consequences of such injuries can be serious,
23,24
13
25
386
P A R T V I I Surgical Treatment Modalities: Lumbar Spine
resulting in limited ambulation, chronic pain, depression, and loss of independence. The primary goals for treatment include pain control and treatment, surgical or nonsurgical, aimed at returning the patient to full activity
as quickly as possible to avoid long-term sequelae of deconditioning and
muscle weakness.
Surgical options for vertebral body compression fractures include vertebroplasty and kyphoplasty to inject bone cement into the collapsed vertebrae with or without the use of an inflatable balloon to elevate the endplates
prior to injecting the cement. Both procedures provide short-term improvement in pain and correction of the deformity, and long-term benefits for
functional capacity and prevention of recurrent pain.
30
A recent meta-analysis30 comparing kyphoplasty and vertebroplasty
found that both treatments resulted in significant improvements in pain and
functionality compared to baseline. Compared to medical treatment there
was improvement in function, but not pain. Comparing the two surgical
treatments, this meta-analysis concluded that balloon kyphoplasty provided
better correction of the kyphotic angle and vertebral height while also having less complications from cement extravasation and pulmonary embolism.
This study concluded that balloon kyphoplasty is likely superior to traditional vertebroplasty for compression fractures refractory to conventional
medical therapy; however they based their assessments on level III data
because no randomized control trials were available to appropriately evaluate these treatments.
30
Newer alternatives to the traditional polymethylmethacrylate (PMMA)
bone cement used for these procedures are also being evaluated. The current cement material has a number of shortcomings including a strong exothermic polymerization reaction, which could damage surrounding tissues,
lack of bioavailability and osteoconductivity, toxicity of the cement, and
extremely limited resorption over time.
31,32
Thus newer cements are being
developed to address some of these issues. A recent study evaluating the use
of two novel variants (aluminum-free and zinc-based glass polyalkenoate
cement) in an in vitro model of osteoporotic compression fractures found
them to have similar material properties (injectability, radiopacity, uniaxial
compression strength, and biaxial flexural modulus) to traditional cement
and performed well over serial compression tests in the lab.
33
Clinical trials for some of these new cement alternatives have begun
with differing results. One study of calcium phosphate cement in balloon
kyphoplasty demonstrated improvement in pain and disability outcomes,
but poor resistance to flexural, tractive, and shear forces, which resulted in
radiographic loss of correction.
34
The authors ultimately recommended
against the routine use of this cement alternative to traditional PMMA.
The hope for future advances in cement technology is to develop materials that will accomplish the pain relief and structural correction in the short
term while allowing gradual bony healing and replacement of the cement
with new bone in the long run. Future research must be done for developing
both the basic material science and clinical efficacy before cement alternatives are widely accepted.
Nonfusion Applications: Addressing Disc Degeneration Directly
Much of low back pain in the aging spine is believed to be a result of
disc pathology. Various studies have attempted to identify changes in
disc anatomy that may play a role in the generation of back discomfort.
Recent studies have demonstrated that there is an overall decrease in cellular density within the disc as well as a reduction in the production of
cartilage-specific extracellular matrix components.
is an overall loss of water-binding capacity and thus an alteration in the
biomechanics of the disc. Despite the paucity of cells within the disc, it
plays an integral role in the maintenance of matrix proteins. The reduction
in cells during aging is believed to be attributable to both apoptotic and
necrotic processes. A focus of recent scientific work has been to induce or
augment these cells.
36
Cellular transplantation offers potential promise in
the treatment of degenerative disc disease; other therapies that have been
proposed are the injection of biomaterials into the disc to augment the
nucleus pulposus.
However, as noted previously, these technologies are very early in their
development from a clinical standpoint. Most of these technologies are only
being evaluated for use early in the degenerative cascade. By the time that
35
As a result, there
degeneration is more advanced, such as in the elderly population being considered here, this technology may not be applicable.
CONCLUSION
Performing spinal surgeries in the elderly presents significant challenges to
the surgeon with regard to advanced pathology and preexisting illness, which
may complicate the treatment options. Iliac crest autograft has long been the
gold standard treatment option for patients of all age groups because it is
the only graft option that contains osteogenic cells, osteoinductive growth
factors, and an osteoconductive matrix. Unfortunately, harvesting autograft
also forces the patient to undergo an additional invasive procedure, which
can result in significant postoperative morbidity, particularly in the elderly.
The evolution of bone graft alternatives and supplements provides exciting,
less morbid alternatives to the use of iliac crest autograft for spinal fusion
that may be considered for use alone or in combination with local bone graft
material.
The use of biologics in the elderly offers the potential to reduce complications associated with harvesting ICBG while maintaining successful fusion.
A number of different types of biologics are currently available, including
various recombinant growth factor signaling proteins (rhBMPs), demineralized bone matrix, and synthetic ceramics. The future of these technologies
likely lies in composite grafts that use these and other biologic materials in
combination to attempt to recreate and stimulate the native bone formation
system. There are similar advances being made in nonfusion alternatives to
surgery, such as in the treatment of vertebral compression fractures in the
elderly, an increasingly common condition as the population ages and osteoporotic, fragility fractures become more prevalent. New cements used for
these treatments are being developed as alternative to PMMA bone cement
and will likely play an increasingly important role in the future treatment of
vertebral compression fractures. Additionally, there may be a role for biologics to assist in the restoration of disc health. This may be accomplished
through possible chondrocyte transplantation or through the use of BMP.
This may offer the possibility of avoiding the cascade of degenerative spine
disease.
As these graft alternatives continue to advance, it will be important to
carefully evaluate their use in the elderly, who are the most likely to require
surgery for degenerative, age-related conditions of the spine. However,
regardless of how these new technologies are employed, the success of these
complex surgeries will remain dependent upon the basic principles essential to achieving a solid arthodesis: proper patient selection, optimization
of the biological environment and selection of the best bone graft material,
preparation of the fusion bed, and maintenance of adequate biomechanical
stability during bone formation.
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Minimally Invasive Spinal Surgery
(MISS) Techniques for the Decompression
of Lumbar Spinal Stenosis
Zachary A. Smith, Farbod Asgarzadie, and Larry T. Khoo
59
k e y p o i n t s
Lumbar spinal stenosis has classically been treated via decompressive
techniques, such as laminotomy, laminectomy, and foraminotomies, which are
traditionally associated with a good early postoperative neurological outcome.
Because the targeted population is elderly, however, perioperative and
postoperative complications, such as wound infections, deep vein thrombosis,
and stasis types of events, are not uncommon.
Traditional wide bony decompressive techniques as well as their attendant
musculoligamentous injury are associated with delayed instability, recurrent
stenosis, and progressive back pain in a significant percentage of patients over
time.
Minimally invasive surgical techniques are associated with decreased
tissue exposure and injury, thereby sparing the stabilizing soft tissue
musculoligamentous and bony complexes.
As a result, published perioperative complication rates for minimally
invasive spinal surgery (MISS) decompressive techniques have been lower
than traditional open decompressive rates, with equivalent 1- and 2-year
neurological outcomes and efficacies. Preliminary long-term data also indicate
a trend toward decreased rates of progressive axial back pain, recurrent
stenotic symptoms, and delayed radiographic instability.
New stabilizing interspinous and interfacet devices may effectively
decompress vertical stenosis (i.e., neurological compression due to facet
subluxation at the level of the spinal recess and foramina) without the need
for excessive resection of the bony elements via classical midline approaches.
INTRODUCTION
In elderly patients afflicted with lumbar spinal stenosis (LSS), the simple act
of walking can often be rendered so painful as to be unbearable. Although
standard open posterior laminectomy is well established and familiar to virtually all spine surgeons, this traditional surgical treatment of LSS is often
associated with significant postoperative pain, disability, and dysfunction.
With their mobility limited by the pain of recovery, these patients can also
suffer from other perioperative sequelae, including deep vein thrombosis,
pulmonary atelectasis, pneumonia, gastritis, ileus, pulmonary embolism,
urinary tract infections, and pyelonephritis. Because LSS patients are typically elderly and frail, the morbidity of the two-edged surgical sword cuts
particularly deep in them. Primum non nocere. Thus surgeons have increasingly employed less destructive means of achieving decompression in the
hope of minimizing iatrogenic injuries.
Minimally invasive foraminotomies and discectomies have gained
increasing popularity among spine surgeons for the treatment of herniated
intervertebral discs. The minimally invasive miscroendoscopic discectomy
has been particularly attractive for its small skin incision, gentle tissue dissection and excellent visualization. The technique has been shown to provide
388
symptomatic relief equivalent to that achieved with open discectomy, with
significant reductions in operative blood loss, postoperative pain, hospital
stay, and narcotic usage. The evolution of minimally invasive techniques has
led to safe and effective applications for the treatment of LSS. The minimally invasive percutaneous microendoscopic approach for bilateral decompression of lumbar stenosis via a unilateral approach has been described for
the treatment LSS and has been shown to offer a similar short-term clinical
outcome as compared to open techniques with a significant reduction in
operative blood loss, postoperative stay, and use of narcotics.
reviews the pathophysiology of LSS; explains the rationale, indications and
surgical techniques for minimally invasive LSS surgery; and presents our
4-year outcomes data.
1
This chapter
PATHOPHYSIOLOGY
The clinical entity of lumbar spinal stenosis is one that is familiar to almost
all physicians who treat the elderly. From a pathophysiological perspective,
lumbar stenosis typically results from a complex degenerative process that
leads to compression of neural elements from a combination of ligamentum
flavum hypertrophy, preexisting congenital narrowing (e.g., trefoil canal),
intervertebral disc bulging or herniation, and facet thickening with arthropathy of the capsule soft tissues.
in imaging, it has become evident that the majority of these changes and
thereby the neurological compression are typically seen at the level of the
interlaminar window.
responsible for the clinical symptoms of lumbar stenosis. For these patients,
the sine qua non feature of the history is low back and proximal leg pain
that worsens with standing and walking and is alleviated by sitting and
bending forward. Whether this phenomenon occurs as a result of direct
neural compression or from secondary vascular ischemia of the nerve roots
remains unclear. Nevertheless, this presentation of neurogenic claudication,
anthropoid posture, and low back pain is becoming increasingly common as
our population demographic grows older and older. Indeed, stenosis of the
lumbar canal is now the most common indication for surgery of the spine
for patients over the age of 65 years.
population makes the surgical treatment of spinal stenosis particularly difficult because these patients are at significantly increased surgical risk because
of their often poor medical condition.
2,5
2-4
With the unparalleled recent advances
These pathological changes are thus thought to be
6-9
This peak incidence in the geriatric
TREATMENT OPTIONS AND GUIDELINES
The traditional treatment of lumbar stenosis usually entails an extensive
resection of posterior spinal elements such as the interspinous ligaments,
spinous processes, bilateral lamina, portions of the facet joints and capsule,
and the ligamentum flavum. Additionally, wide muscular dissection and
retraction usually are required to achieve adequate surgical visualization.
These classical operations of a wide decompressive laminectomy, medial
C H A P T E R 5 9 Minimally Invasive Spinal Surgical (MISS) Techniques for the Decompression of Lumbar Spinal Stenosis
389
facetectomy, and foraminotomy have been used for decades with a variable
degree of success.
8-11
Such extensive resection and injury of the posterior
osseous and muscular complex can lead to significant iatrogenic pain, disability, and morbidity. Loss of the midline supraspinous–interspinous ligament complex can lead to a loss of flexion stability, thereby increasing the
risk of delayed spinal instability.
12,13
Extensive laminectomy can also be
associated with significant operative blood loss as well as prolonged postoperative pain and weakness secondary to the extensive surgical dissection and
muscle detachment. Such iatrogenic injury can lead to paraspinal muscle
denervation and atrophy, which may correlate with an increased incidence of
“failed back syndrome” and chronic pain.
14,15
Because patients with lumbar
stenosis are usually elderly and often medically frail, this delayed recovery
can often result in significant morbidity. Deep venous thrombosis, pulmonary embolism, pulmonary atelectasis, pneumonia, urinary tract infections,
ileus, and narcotic dependency are but some of these potentially devastating
sequelae.
Whereas conservative therapy initially is a reasonable recommendation,
there will inevitably be a significant proportion of patients with progressive stenotic symptoms who will ultimately require surgical intervention. In
the Maine Lumbar Spine Study group, Atlas and coworkers
16
prospectively
followed 97 patients over a 10-year interval. Of these, 56 were surgically
treated and 41 were conservatively managed. Based on patient satisfaction
assessment vehicles, 54% of surgically treated patients reported improvement versus 42% of nonsurgical patients at 10 years. In comparison, the
4-year data from the Maine Lumbar Spine Study group revealed that 70%
of surgically treated patients reported a clear improvement, compared to
52% in the nonoperative group.
6
This decrease in patient satisfaction indicates that surgical benefits may not be stable over the course of time because
LSS is typically a chronic and progressive disease. Hurri and colleagues,
in 1998, reported their longitudinal 12-year study of 75 patients with lumbar stenosis. Using the Oswestry index, their disability was scored over
many years and could demonstrate no clear difference between those who
were operated on versus those managed conservatively. From an extensive
review of the literature, Turner concluded from his attempted meta-analysis
that approximately 64% of surgically treated patients had a good outcome
over a midterm period of follow-up (3 to 6 years). However, he also noted
that delayed clinical progression and recurrence of stenosis symptoms was
extremely common, thus reflecting the chronic degenerative nature of the
underlying disease process.
13
Thus although surgical treatment appears to
have a positive effect on the natural history of LSS, clinical progression
and recurrence is likely. Moreover, several subgroups have been consistently
identified that are particularly prone to recurrence of symptoms. These
include patients with preexisting spondylolisthesis, scoliosis, prior destabilizing laminectomies, and the presence of segmental vertebral motion on
flexion–extension radiographs.
17,18
According to the treatment guidelines
set forth by the AANS/CNS Joint section on Disorders of the Spine and
Peripheral Nerves, fusion is recommended for patients with lumbar stenosis
and associated degenerative spondylolisthesis who require decompression.
In addition, wide decompressions leading to disruption of the facet joints
has also been associated with poorer outcomes.
19
In light of these considerations, the need for a less invasive means of decompression without major
disruption of the facet joints and muscular attachments as well as the option
of fusion for the treatment for LSS is evident.
SURGICAL RATIONALE
Over the past two decades, numerous surgeons have worked toward the
goal of reducing the surgical morbidity of the procedure. The ideal operation for LSS would be one that could simultaneously achieve an adequate
decompression of the neural elements, while at the same time minimize
damage to the posterior muscular, ligamentous, and bony complex. Because
the pathological changes typically are concentrated at the level of the interlaminar space, focal laminotomy was the natural first step in the evolution
of surgical procedures for LSS. By sparing most of the lamina, spinous
processes, and interspinous ligamentous complex, laminotomy helped to
preserve the biomechanical integrity of the spine. Aryanpur and Ducker,
in their description of multilevel open lumbar laminotomies, reported
a longitudinal good outcome rate of 79% to 85% at 2-year follow-up. As
the use of the operating microscope became increasingly common among
spinal surgeons, unilateral microscopic hemilaminotomy was developed as
a means of sparing the contralateral musculature as well. This procedure
was characterized by unilateral multifidus retraction, ipsilateral decompression, and also contralateral microscopic decompression performed under the
midline bony and ligamentous structures. For this microscopic laminotomy
as described by McCulloch
21
and Young and colleagues,22 an 80% to 95%
improvement rate was reported over a 9-month follow-up period. Despite
this progressive movement toward less extensive resection of the posterior
bony elements, symptomatic outcomes have remained similar regardless of
the aggressiveness of the surgical procedure utilized to treat LSS.
in one of the only studies correlating the degree of radiographic with clinical
outcome, it was observed that the satisfaction of patients with the results of
surgery (e.g., Oswestry score and walking capacity) was more important in
surgical outcome than the degree of decompression as seen on a postoperative CT scan.
5
In the past decade, significant strides in microendoscopic visualization
technology have been made. Accordingly, endoscopic-assisted procedures
have become increasingly popular for the treatment of a wide range of spinal
pathologies, including hyperhydrosis, herniated discs, tumors, and fractures.
In the lumbar spine, microendoscopic-assisted discectomies (MEDs) have
been used in treating herniated discs successfully for the last 5 years. The
MED procedure has been particularly attractive for its small skin incision,
gentle tissue dissection, excellent visualization, and ability to achieve results
equivalent to those with open techniques. The microendoscopic decompressive laminotomy (MEDL) technique was thus developed as a synthesis
of the unilateral hemilaminotomy, described earlier, and these MED techniques. The MEDL technique was initially validated in a series of cadaveric studies in which the equivalent bony decompressions were achieved via
7
either an open or an endoscopic technique.
studied clinically with resultant good surgical outcomes, low morbidity, and
a rapid postoperative functional recovery.
24
Since then, it has also been
1
A bilateral decompression via a
unilateral minimally invasive approach thus represents the next logical step
in the evolution of modern surgical treatment for LSS.
INDICATIONS FOR MISS DECOMPRESSIVE TECHNIQUES
Patients undergoing microendoscopic decompressions for LSS should meet
the same selection criteria as those for open decompressive laminectomy or
laminotomy. As reviewed earlier, these patients should have low back pain
associated with the sine qua non description of neurogenic claudication.
Because the MEDL technique is capable of decompressing the central canal,
lateral recess, and the proximal part of the ipsilateral neural foramen, symptoms of radiculopathy from either foraminal stenosis or disc herniation can
be successfully addressed by MEDL as well. When evidence of nerve compression is present, the MEDL should ideally be performed on the same side
as these symptoms to afford maximal surgical exposure. Patients who have
19
radicular symptoms on both sides should either be treated via a bilateral
MEDL procedure or open type decompression. Similarly, a far-lateral disc
herniation with coexisting central stenosis must be treated via either two
MED approaches or an open technique.
Patients with evidence of LSS in addition to spondylolisthesis, deformity, or severe degenerative disc disease may benefit from a minimally
invasive transforaminal interbody fusion and percutaneous posterolateral
instrumentation.
mity, infection, tumor, arachnoiditis, pseudomeningocele, or cerebrospinal
fluid fistula are generally not suitable candidate for MEDL. A thorough
clinical and radiographic evaluation with use of dynamic flexion, extension,
and lateral-bending radiographs, contrast-enhanced MRI and CT, and isotope scans should be performed to exclude these conditions. Prior surgery
at the same level as the present stenotic area is also a relative contraindication. For these cases, significant epidural scarring and dense adhesions can
make the MEDL technique particularly difficult with an increased risk of
durotomy. However, in cases with a limited amount of decompression, a
relatively intact facet complex, and little epidural scarring as shown on gad-
20
olinium-enhanced MRI, the MEDL procedure can be used to successfully
achieve a repeat decompression. Redo procedures should be attempted only
by surgeons who have already gained facility with the MEDL technique
in a good number of simple cases. Additionally, patients undergoing redo
19
Patients with severe spondylolisthesis or severe defor-
23
Indeed,
390
P A R T V I I Surgical Treatment Modalities: Lumbar Spine
decompression with MEDL should be clearly informed about the increased
surgical risks and the possibility of conversion to an open procedure.
Surgical Technique
After appropriate preoperative evaluation and medical clearance, the patient
is brought to the operative suite where general endotracheal anesthesia is
induced with adequate intravenous access and an intraarterial monitoring catheter. Local and intravenous sedation alone is generally inadequate,
because the MEDL procedure requires the patient to be still for a prolonged
period of time. A Foley catheter should be used for most cases. After induction, we refrain from the use of neuromuscular paralytics to better assess the
nerve root during decompression. This will provide for intraoperative feedback as well as to allow for a more rapid reawakening of the patient at the
end of the procedure. Because blood loss for the MEDL procedure has typically been minimal, it is important to avoid excessive fluid hydration during the case, which can often lead to cardiopulmonary complications in this
population of older patients. Overall, it is crucial for the operative surgeon
to have a clear working dialogue with the anesthesiologist before and during the case to clarify the nature of the procedure. This will greatly help to
reduce unfortunate miscommunications and their attendant complications.
The patient is then turned into a prone position onto a radiolucent Wilson frame and Jackson table. Utmost care should be made to insure adequate
padding of all pressure points, eyes, and extremities. The fluoroscopic Carm should then be brought into the surgical field so that real-time lateral
fluoroscopic images can be obtained. Ideally, this should be draped and positioned such that it can be easily swung in and out during the procedure
without having to interrupt the flow of the case. The operative surgeon generally stands on the side of the approach with the C-arm and video monitors placed opposite him. However, the ultimate arrangement of the video
monitor and C-arm monitor can be varied to allow for optimal ergonomic
movements during the operation (Figure 59-1). Electromyographic (EMG)
monitoring of motor nerve root responses can be used if desired.
Under fluoroscopic guidance with a Steinmann pin held laterally to
the patient, the approximate level of the incision is marked approximately
1 to 1.5 inches off midline on the side of the approach. This incision is
marked to facilitate targeting of the laminofacet junction at the spinal level
to be decompressed (Figure 59-2A). A small stab incision is then made in
the middle of the marked incision through which the Steinmann pin is then
passed down to the medial bony facet margin. Particular care should be
made to begin this approach laterally to avoid inadvertent dural penetration. The placement of the pin is then confirmed with the fluoroscope to
ensure a good working trajectory (Figure 59-2B). Although we have not
routinely done so, anteroposterior radiographic images can be obtained to
guarantee proper pin positioning. In our early experience with minimally
invasive stenosis decompression, we decompressed the ipsilateral lateral
recess before decompressing the contralateral side. For the last 4 years, we
have changed our approach to contralateral decompression, a technique
that has been described previously.
25
Once the guidewire has been docked
on the spinolaminar junction, a skin incision is made above and below the
Steinmann pin for a total length of approximately 2.5 cm. The METRx
(Medtronic, Sofamor-Danek, Memphis, Tenn.) microendoscopic system’s
set of serial dilators (Figure 59-3) are then passed over then Steinmann pin
to gently dilate the lumbar musculature and expand the lumbodorsal fascia
away. Medial angulation of up to about 45 degrees is desirable at this point
to ensure optimal visualization of the spinolaminar junction and ensure a
proper trajectory for drilling of the anterior aspect of the lamina to the contralateral lateral recess and foramen (Figure 59-4). The 18-mm final working channel is then passed over the dilators and secured to the flexible-arm
METRX retractor mounted to the table side rail. Final fluoroscopic confirmation of the working channel position is then obtained, an 18-mm working
channel of adequate depth (usually 5 to 6 cm) is placed and the serial dilators
are then removed. The endoscope is then attached to the tubular retractor or
the operating microscope is used for the remainder of the procedure.
Bovie cautery with a long tip is then used to remove the remaining
muscle and soft tissue overlying the lamina and spinolaminar junction. A
long high-speed burr (e.g., AM-8, Midas Rex) is then used to core out the
cancellous and deep cortical surface of the contralateral lamina, preserving
the ligamentum flavum underneath and using it as a protective layer over the
dura. This “intralaminar” drilling is carried out laterally to the contralateral
lateral recess and foramen. Kerrison rongeurs may be used to remove the
remaining laminar edge and the medial contralateral facet. After adequate
contralateral bony decompression, the ligamentum flavum can be removed
with use of up-angled curettes and Kerrison rongeurs.
A
Monitor
Surgeon
F IG UR E 5 9- 1 A view of the typical operative set-up for an MEDL pro-
cedure. The patient is placed in the prone position. The C-arm is placed into
the field to allow for intraoperative lateral fluoroscopy. The video monitors are
placed opposite the operative side to allow easy visualization by the surgeon.
C-arm
B
F IG UR E 59 - 2 A, Dorsal view of interlaminar space with highlighted
spinolaminar junction target. B, Lateral fluoroscopic image showing percutaneous Steinmann pin placement.
C H A P T E R 5 9 Minimally Invasive Spinal Surgical (MISS) Techniques for the Decompression of Lumbar Spinal Stenosis
B
A
C
F IG UR E 5 9 -3 METRx (Medtronic Sofamor Danek, Memphis, Tenn.).
Equipment Set. A, Sequential soft tissue dilators. B, 18-mm working channel
with retractor arm attachment. C, Flexible bed-mounted retractor arm.
391
Attention is now directed toward the ipsilateral lateral recess and foramen. The tubular retractor is angled laterally toward the ipsilateral laminamedial facet junction and drilling is carried out to thin the lamina and
the medial facet complex down (Figure 59-5). With the bony edges well
visualized, a small straight curette is used to scrape the inferior edge of the
adjacent lamina and the medial edge of the facet complex. This exposure is
then carried underneath the lamina and facet with the use of a small angled
endoscopic curette (Figure 59-6 A and B). Proper placement of the curettes
should be confirmed under fluoroscopy. Good dissection of the underlying
flavum and dura from the bone is crucial in preventing incidental dural tears
and cerebrospinal (CSF) fluid leaks. Bleeding from epidural small and edge
of the flavum was controlled via long-tipped endoscopic bipolar cautery. A
small angled Kerrison rongeur is then utilized to begin the laminotomy (see
Figure 59-6 A to D). After adequate drilling, endoscopic Kerrison rongeurs
are used to continue the removal of the lamina and medial facet. Frequent
dissection with the small angled curette before biting with the Kerrison rongeur should be used to free the underlying ligament and nerve root. In this
fashion, bilateral hemilaminotomies, medial facetectomies, and foraminotomies are completed (Figure 59-7).
For cases in which an ipsilateral bulging or herniated disc is present, the
nerve root is retracted and the epidural veins are coagulated with bipolar
cautery and dissected free over the underlying disc space. A sharp annulotomy is then made with a special endoscopic knife and a standard discectomy
and internal decompression is then performed.
In cases of multiple adjacent level stenoses, the initial placement of the
dilators and tubular retractor should be midway between the stenotic levels.
In a patient with both L3-L4 and L4-L5 stenosis, for example, the working
channel should be first docked on the L4 lamina and then swung caudad to
decompress the L4-L5 level, and cephalad to subsequently decompress the
L3-L4 level. For patients with a larger vertical distance between spinal segments, sharp incision of the lumbodorsal fascia and superoinferior translation of the working channel may also be needed. Figure 59-8 demonstrates
the extent of multiple level decompression than can be obtained through
repositioning of the working channel through a single incision. Figure 59-9
demonstrates a typical decompression achieved via MEDL for a representative case of lumbar stenosis.
F IG UR E 5 9 -4 Medial angulation of the retractor tube ensures optimal
visualization of the spinolaminar junction and facilitates a proper trajectory for
drilling of the anterior aspect of the lamina to the contralateral lateral recess
and foramen.
F IG UR E 5 9 -5 The tubular retractor is now angled laterally toward the
ipsilateral lamina–medial facet junction.
392
P A R T V I I Surgical Treatment Modalities: Lumbar Spine
A
C
F IG UR E 5 9 -6 The MEDL technique utilizes standard techniques of decompression through the working channel under endoscopic guidance: A, A small
angled curette is used to define the laminar edge and to mobilize the flavum. B, An intraoperative view through the endoscope of this maneuver is shown.
C, Endoscopic Kerrison rongeurs are used to begin the laminotomy and decompression. D, An intraoperative view of the Kerrison used for the laminotomy.
B
D
In cases in which an interbody fusion is indicated, the drill is used to
remove the medial aspect of the superior articular process and expose the
superior and medial aspects of the pedicle and the adjoining foramen to the
level of the top margin of the disc. Coagulation and division of the inferior
foraminal veins allows for about 10 to 12 mm between the exiting and traversing roots at the upper margin of the disc, allowing for thorough discectomy and interbody fusion using a single intervertebral spacer is then placed
and directed just across the midline using biplanar fluoroscopy (Traxis MIS
TLIF set, Abbot Spine, or Concorde Cage, Depuy Spine) (Figure 59-10).
Bilateral percutaneous pedicle screws and connecting rods (Pathfinder,
Abbott Spine) are placed under compression to lock the interbody fusion
cage and to minimize the risk of cage migration.
26
A detailed discussion of
a minimally invasive transforaminal lumbar interbody fusion is beyond the
scope of this article.
After inspection of the thecal sac and nerve roots, hemostasis is obtained
by bipolar cautery and gentle tamponade with thrombin-soaked Gelfoam
pledgets. A single dose of intraoperative Cefazolin (Ancef ) or vancomycin
is typically employed during the procedure and a second dose can be given
at the surgeon’s discretion. The area is then copiously irrigated with lactated
ringers impregnated with bacitracin antibiotics. A small piece of Gelfoam
soaked with methylprednisolone (Solumedrol) was typically gently placed
over the laminoforaminotomy defect. Use of epidural morphine paste or
similar cocktails is reasonable if there is not evidence of dural erosion or
tear. Such agents may help to reduce postoperative pain and allow for more
rapid recovery and ambulation. The tubular retractor and endoscope are
then removed. Because the defect is typically quite small, only a limited
F IG UR E 5 9 - 7 Bilateral hemilaminotomies, medial facetectomies, and
foraminotomies are completed.
amount of closure need be performed and a drain is not needed. A 0-Vicryl type of reabsorbable suture is used to close the lumbodorsal fascia in a
C H A P T E R 5 9 Minimally Invasive Spinal Surgical (MISS) Techniques for the Decompression of Lumbar Spinal Stenosis
Patients should be allowed to ambulate early on after surgery. Foley
catheters, arterial lines, and unneeded intravenous lines should be removed
as early as possible. Early evaluation and treatment by experienced physical therapists are important to begin the recovery and rehabilitation
process. As most patients with LSS present with a limited capacity for
ambulation, walking at the preoperative level should be encouraged. We
typically have not used a rigid external orthosis after MEDL with or without TLIF and pedicle screw fixation, but use of a lumbar corset with metal
stays or similar brace is reasonable for the patient’s comfort. Depending
S1
L5
L4
on the level of analgesic and narcotics used preoperatively, we have generally aimed to minimize usage of postoperative pain medications. We typically employ strong nonsteroidal antiinflammatory agents in nonfusion
cases (e.g., celecoxib [Celebrex], rofecoxib [Vioxx]) combined with muscle
relaxants (e.g., cyclobenzaprine [Flexeril], baclofen, methocarbamol [Robaxin]). Oral narcotic medications such as hydrocodone/acetaminophen
(Vicodin) and oxycodone/acetaminophen (Percocet) are used primarily
A
on a breakthrough basis. In a comparison of MEDL with open decompression, we found that LSS patients after MEDL use significantly less
narcotic medication.
1
Patients are typically discharged when they are able to ambulate on their
own and their pain on oral agents only. For patients with mild to moderate
preoperative symptoms and gait limitation, discharge can frequently occur
within 24 to 48 hours after surgery. For patients with long-standing severe
symptoms and gait dysfunction, a course of inpatient rehabilitation may be
needed to optimize their functional status before sending them home. It is
important to inquire about the patient’s home living situation to ensure that
L3
L4
L5
appropriate support and safety is available there before discharge. We routinely recommend a structured course of truncal stabilization and aerobic
conditioning for these patients.
393
B
F IG UR E 5 9 - 8 Intraoperative fluoroscopic images demonstrate the
long multilevel decompression that can be achieved through a single incision by
simply angling the working channel.
figure-of-eight. Bupivacaine (Marcaine [0.25%]) is used to inject the skin
edges before closure. Inverted stitches of 2-0 Vicryl suture are used to close
the subcutaneous layer. A 4-0 clear Vicryl subcuticular closure is then used
to carefully reapproximate the skin edges, with care taken to avoid inversion. Either Steri-Strips or Dermabond can then be used to cover the skin.
Dermabond is attractive because it keeps the skin edges closely approximated for 7 to 10 days and provides a waterproof barrier. The patient can
thus shower almost immediately after surgery.
For cases in which a CSF leak occurred, direct repair of the durotomy
is extremely difficult because of the small size of the endoscopic procedure.
Fortunately, most dural tears that occur with the microendoscopic technique
are typically small as well. Thus we have typically not employed lumbar
drains. Fibrin glue, fat, or muscle grafts were typically used to tamponade
the dural violation. For large CSF leaks, direct repair can be attempted if
specialized instruments are available for use through the endoscopic tube. A
Castro-Viejo type of needle holder and long forceps are particularly useful
in this regard.
POSTOPERATIVE MANAGEMENT
The patient is awakened from anesthesia and taken to the postanesthesia
recovery unit. For single-level MEDL procedures, for which an early discharge is anticipated, it is important for the surgeon to communicate preoperatively with the anesthesiologist. Long-acting inhalational and intravenous
agents should be avoided to allow for rapid awakening of the patient postoperatively. Additionally, use of only short-acting muscle relaxants for initial
induction will allow for better monitoring of nerve root function as well as
quicker extubation of the patient after surgery.
CLINICAL OUTCOMES AND COMPLICATIONS
The results of our first 48 MEDL patients are presented here to serve as a
useful guide in what to expect during clinical follow-up. As with all surgical procedures, the results of treatment with MEDL will vary directly with
the patient population and selection criteria of the surgeon. Additionally,
operative times, blood loss, complication rates, and postoperative length of
stay will typically improve as a surgeon’s facility with the MEDL procedure
grows.
The patients had a mean age of 64.5 years. There was a male-to-female
ratio of 3:2. The patients’ clinical presentations were scored into four clinical categories: back pain, leg pain, gait limitation and distance, and urinary
dysfunction. Patients who underwent fusion and patients with evidence of
lumbar instability, severe deformity, spondyloptosis/severe spondylolisthesis, infection, tumor, and cauda equina syndrome were excluded from the
MEDL study group. All patients had pain in their lower back, 80% reported
some degree of radiating leg pain, about 96% had significant limitation in
their ambulatory ability, and about 16% reported symptoms of urinary
dysfunction. Before surgery, all MEDL patients demonstrated compressive
central canal stenosis with or without lateral recess stenosis on MRI or CT
myelogram. A historical comparative cohort of 32 patients with LSS of similar age and symptoms, and of the same gender, from the same institution
treated via open laminectomies were used as a comparison.
Twenty-eight patients had a one-level procedure performed, with 20
patients having two levels done at one sitting. Overall, a total of 68 spinal
segments were decompressed in the 48 patients. Typically, the choice of side
for the surgical approach was that of the most clinically symptomatic side.
The operative time for a single-level MEDL procedure averaged 55 minutes.
The average blood loss per level decompressed was 25 ml for the MEDL
group and 193 ml for the open group. No patients in the MEDL group
required intraoperative or postoperative transfusions.
Our rate of dural violations and CSF leak is 4% compared to previous
rates of up to 16%.
nosis decompression, we decompressed the ipsilateral lateral recess before
decompressing the contralateral side. We believe that this approach may
in fact increase the risk of dural violations while drilling the contralateral
side, since unprotected dura is exposed. With the technique described
earlier and published previously,
sides during contralateral drilling. There were no cases of neural injury
1
In our early experience with minimally invasive ste-
25
the dura is entirely protected on both
394
P A R T V I I Surgical Treatment Modalities: Lumbar Spine
A
FI G U RE 5 9 -9 Illustrative case of a 57-year-old man who presented with a 16-month history of neurogenic
claudication type symptoms and some left-sided L5 radicular symptoms. A, CT myelogram shows marked L4-L5 stenosis
from facet and flavum hypertrophy. B, Postoperative CT demonstrates the extent of decompression afforded by MEDL.
F IG UR E 5 9- 10 Illustration depicting insertion of intervertebral spacer
through a retractor tube.
associated with the MEDL cases, and to date there have been no cases of
iatrogenic or delayed spinal instability requiring fusion.
The average length of stay for the MEDL and open surgery patients
was 36 hours as compared to the significantly longer average stay of 94
hours for open surgery patients. The length of stay was often affected by
postoperative problems arising from the often numerous comorbid medical conditions that these elderly patients often had. Of 48 patients with
LSS initially enrolled, 4-year outcomes are available on 32 patients. All
B
patients reported an increase in walking endurance at 6 months that was
maintained in 80% of patients at a mean of 38 months. Satisfaction of
patients at 4 years was reported by 78% of the patients, with 88% reporting
improvement in symptoms. Overall, the ODI scores were as follows: 46
preoperatively, 20 at 1 year, 21 at 2 years, 26 at 3 years. The SF-36 scores
went from an average of 2.2 preoperatively, 3.1 at 1 year, 2.9 at 2 years, and
2.8 at 3 years.
EMERGING TECHNOLOGIES
Although this chapter focuses primarily on direct decompressive techniques
for LSS, posterior lumbar arthroplasty devices may provide symptomatic
relief without direct decompression. The simplest posterior lumbar arthroplasty devices are those of interspinous distraction or blockade devices.
These include the X-STOP (Saint Francis Medical, Alameda, Calif.), the
Wallis System (Abbott Spine, Austin, Tex.), the Diam Device (Medtronics, Memphis, Tenn.) and the Coflex system (Paradigm Spine, New York,
N.Y.) (Figure 59-11). These devices are placed between the bases of the
spinous processes and provide mild distraction or blockade of the functional
middle column at a given motion segment. As a result of this interposition,
the volume and height of the spinal neural foramen and the lateral recess are
maintained and/or slightly increased. Zucherman and colleagues
191 patients were treated, 100 in the X-STOP group and 91 in the control
group. At every follow-up visit, X-STOP patients had significantly better outcomes in each domain of the Zurich Claudication Questionnaire.
At 2 years, the X-STOP patients improved by 45.4% over the mean baseline Symptom Severity score compared with 7.4% in the control group;
the mean improvement in the Physical Function domain was 44.3% in the
X-STOP group and −0.4% in the control group. In the X-STOP group,
73.1% patients were satisfied with their treatment compared with 35.9% of
control patients.
Additionally, biomechanical cadaveric and finite modeling studies have
demonstrated an increased overall stiffness of the motion segment, presumably from middle column augmentation, as well as decreases in the stresses
and loading across the posterior aspect of the intervertebral disc and annu-
27
reported