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56
J. C. Patt and D. P. Leas
failure of stability, but the passive structure of
the spinal column is most commonly the region
affected by metastatic disease [3–5].
Pain continues to be a signicant clinical nding and the most common presenting symptom
in patients with metastatic spine disease [6]. This
pain is an indicator of the failure of the spinal
column to maintain anatomic relationships under
physiologic stresses [2, 7].
As with any initial patient encounter, time must
be dedicated toward a thorough patient interview
and physical exam. It is important to consider that
some patients will already have a preexisting oncologic diagnosis or are in the process of a formal
workup, while others may have been sent from a
primary care provider or an emergency room for
evaluation of pain or neurologic decit. Taking
the time to recognize what the patient understands about their symptoms at baseline will help
in establishing a rapport and improve the ow of
information between parties throughout the visit.
Careful questioning regarding the length and
character of symptoms should elicit enough information to start down a differential path, as well
as help determine whether this patient is at risk
for more rapid progression of symptoms. Classic
descriptors of pain, such as pain with activity, nighttime pain, or progression of symptoms (both pain
and neurologic) over longer periods of time, can be
hints that the patient may suffer from a spine that
is not capable of resisting physiologic stresses and
at risk of mechanical failure. Questions should also
highlight symptoms of neurologic dysfunction,
such as trouble with ne motor skills or balance,
indicative of a myelopathic process, radicular pain
(a very common scenario in the lumbar spine), or
even bowel/bladder changes in a more urgent presentation such as a frank cauda equina syndrome.
Radiographic Evaluation
Before discussing the evidence surrounding imaging of suspected metastatic disease, it is important
to understand the translation of bone loss to actual
instability. Cadaveric studies perfumed by Abumi
etal. provided signicant insight into progressive
instability from the loss of posterior elements.
Two-level lumbar specimens were sequentially
released in stepwise fashion and subjected to
vectored stresses to determine the loss of intrinsic stability, starting with division of the posterior ligamentous complex and working through
unilateral medial facetectomy, bilateral medial
facetectomy, unilateral complete with contralateral medial facetectomy, and nally bilateral total
facetectomy [8]. Their ndings correlated with a
progressive increase in relative range of motion
that has been critical for interpreting ndings of
bone loss in axial and sagittal imaging studies.
Relative increases in exion, lateral bending, and
axial rotation were signicantly different, implying a translation to invivo loss of these structures.
Plain Radiographs
Standing radiographs are of foremost importance
when initiating a workup of pain in the setting of
potential metastatic disease. Standing anteriorposterior and lateral lms allow an outlined look
at existing bony anatomy, providing contrast
between adjacent levels of normal and abnormal
bony structure [9]. An upright lm or gravity stress
view is the simplest form of a stress radiograph of
the spine. An interesting direct translation of the
work done evaluating the contribution of the posterior facet structure to spinal stability is the “winking owl” sign. In this case, the A/P lm shows an
absence of a clinically involved pedicle, causing
the absence of its circular cortical rim (Fig.5.1).
Functional radiographs continue to be a core
component of imaging in the ofce, both at initial encounter and following progressive disease
over time. Dynamic instability can occasionally
be visualized with exion and extension views
either in an upright or lateral decubitus position.
Some authors advocate for a lateral position as it
relaxes the paraspinal musculature and will allow
for a purely passive exam of structural instability.
In a study by Wood etal., they found that 31 of
50 patients demonstrated instability with exion/
extension, and of the 31, 18 were only unstable
on lateral decubitus imaging [10]. This indicated
a potential increase in sensitivity but also a potential increase in false-positive test results.
Nizard and colleagues highlighted, however,
that there are multiple limitations to dynamic
radiography: First, functionally dynamic studies
are difcult to reproduce in patient populations.
5 Spinal Instability inMetastatic Disease
57
compared to supine imaging (x-rays, CT scans,
and MRIs) remain a mainstay in the identication of spinal instability, especially when accompanied by position-dependent pain.
Nuclear Medicine Scans
Nuclear imaging studies are an important tool
in the identication of metastatic disease, but do
not provide any clinical benet with respect to
determining stability or potential need for future
xation. It is routinely utilized as a supplemental
method of detecting skeletal metastases with a
new diagnosis of many soft tissue cancer including breast, lung, prostate, thyroid, renal, and
many others. In some cases, a positive bone scan
can be present 3–18 months before any other
radiographic abnormality appears [13].
Fig. 5.1 A/P radiograph of the thoracolumbar spine. This
patient was diagnosed with metastatic disease erosion of
the left T10 pedicle, as demonstrated by the “winking
owl” sign with the absence of the cortical rim at this level
on the left side compared to adjacent segments
Even small variations in imaging directionality
and patient positioning between studies can
result in up to 10–15% difference in the amount
of perceived translation. Second, while radiographic landmarks have been described, there is
no fundamentally standard technique to image
these patients. And nally, a lack of “gold standard” for the diagnosis of instability means that
any study obtained with conventional radiography
will provide only part of the whole picture [11].
Unfortunately, disease processes can advance
silently even with dedicated serial radiographs
obtained. In an early study by Edelstyn etal., a
cadaveric lumbar spine was sectioned in the sagittal plane, and the cancellous bone of the vertebral body was sequentially removed with interval
radiographs [12]. They found that 60% of the
bone had to be removed before any changes were
detected on lateral imaging, and the entire body
had to be decorticated before it was detectable
on an A/P view. Because of this important limitation, other advanced imaging modalities serve an
important role in characterizing spinal disease.
Despite these limitations, changes in alignment seen as both coronal and sagittal collapse as
Computed Tomography
Computed tomography (CT) continues to be the
gold standard with respect to evaluating bony
anatomy. Sagittal and coronal reformats, in addition to the standard axial sections, provide nearly
all bony parameters needed when dening lesion
size and quality.
Axial cuts provide an excellent look at facet
orientation, most importantly in the lumbar spine.
As these facets become more sagittally aligned,
experience with degenerative spondylolisthesis
has demonstrated a reduced mechanical resistance to listhesis under physiologic loads. These
facets may be at an increased risk for early instability as a disease process progresses (Fig.5.2).
Sagittal and coronal reformats provide measurable information with respect to single-level
translation in a supine position. Asymmetric disc
space collapse can represent early signs of facet
failure and unilateral subsidence. Finally, sagittal
images can also show disproportional interspinous
spacing that may indicate mass effect or compromise of the posterior ligamentous complex.
Magnetic Resonance
Utilization of magnetic resonance imaging (MRI)
in the setting of segmental instability is still in its
early stages. One well-understood benet of MRI
in the setting of spine pathology is its exceptional
soft tissue and uid characterization providing
insight into both specic tumor characteristics
58
ab
J. C. Patt and D. P. Leas
Fig. 5.2 Figure (a, b) demonstrates two adjacent levels in
a patient with back pain and clinical symptoms of instability. Figure (a) demonstrates a more typical alignment of
the lumbar facet orientation. Figure (b) demonstrates
facet articulations in a near completely sagittal plane
where the patient also demonstrated radiographic signs of
instability. This patient went on to instrumented fusion at
this level
and evaluation of potential spinal cord compression/involvement. The increasing prevalence of
upright MRI capabilities and the option for exion and extension imaging would theoretically
provide some information about stability in neoplastic disease; however to date it has only been
described in degenerative disease [14].
Classically, identication of increased uid
signal within the facet capsule is used as an
indication of hypermobility at that level. Data in
this realm exclusively centers on degenerative
cervical and lumbar disease processes. Axial T2
imaging allows for a strong contrast between the
darker bone structures and bright uid within
the facet capsule (Fig. 5.3). Increases in uid
appear to correlate in a linear fashion with instability, and uid space measuring over 1.5 mm
can suggest early instability in the absence of
translation on a supine MRI in degerative dis-
Fig. 5.3 Figure is an axial cut of the lumbar spine with
T2-weighted enhancement. Most notable is the high
intensity of the uid in the right facet complex, particularly compared to the less affected left facet complex
a discussion of the Spinal Instability Neoplastic
Disease Score (SINS).
ease [15–19].
Classication Systems
A number of authors have worked to quantify and
qualify the risk for instability based on clinical
and radiographic characteristics. This section will
outline several of these systems and nish with
Denis
The work done by Francis Denis is well quoted
in the spinal trauma, and with good reason. His
three-column model provides a fundamental
understanding of the different anatomic sections
moving from anterior to posterior, as well as
5 Spinal Instability inMetastatic Disease
59
providing analysis should one or more of these
columns show deciency [20, 21].
In an evaluation of over 400 injuries, Denis highlighted three separate zones of injury in the spine.
This was a departure at the time from the previous
two-column model. These three areas consisted of
the anterior, middle, and posterior columns. The
anterior column includes the anterior longitudinal
ligament, the anterior vertebral body cortex, and
the anterior aspect of the annulus and ends in the
AF
midpoint of the end plate. The middle column starts
at the midportion of the end plate and includes the
posterior annulus, the posterior cortex of the vertebral body, and the posterior longitudinal ligament.
Finally, the posterior column includes the ligamentum avum, the posterior bony elements (pedicle,
lamina, spinous process, facet articulations), and
the inter-/supraspinous ligaments (Fig.5.4).
His retrospective review of injury patterns
in trauma provided insight into the modes of
Fig. 5.4 Three-column model demonstrated by Denis. From Francis Denis, The Three Column Spine and Its
Signicance in the Classication of Acute Thoracolumbar Spinal Injuries, Spine, 1983 Jan 1;8(8)
60
J. C. Patt and D. P. Leas
failure with specic column incompetence. For
example, a spine with an insufcient posterior
column could be at risk for instability in both
exion and rotation. Disruption of the anterior
column would in theory fail in extension due
to the absence of a competent anterior longitudinal ligament. This foundation allowed future
research to incorporate his work into additional
classication systems as we will see moving
forward.
Taneichi
In a thorough assessment of risk factors for thoracolumbar collapse with metastatic disease,
Taneichi et al. took a series of 100 thoracic and
lumbar vertebrae with osteolytic lesions and
captured data points from radiographic studies. Particular data points of interest were tumor
size (in percentage of vertebral body occupancy),
pedicle destruction, posterior element destruction,
and costovertebral destruction. The last three data
points are again well demonstrated to have an
association with clinical instability based on the
cadaveric biomechanical studies done by Abumi
in 1990 [8].
A multivariate logistic regression model demonstrated that costovertebral joint destruction and
tumor size were predictors in the thoracic spine,
while size and pedicle destruction were the leading factors in the thoracolumbar region. These
data points were based on computed tomography
for better bony evaluation.
Ultimately, the following criteria were
selected by the authors as predictive of impending collapse [22]:
Thoracic spine:
50–60% involvement of the vertebral body in
isolation
25–30% involvement of the costovertebral
joint
Thoracolumbar/lumbar spine:
35–40% involvement of the vertebral body in
isolation
20–25% involvement of the posterior
elements
Asdourian
Using a series of patients with metastatic breast
cancer in the vertebral body, Asdourian and colleagues worked to dene a set of criteria for
instability and thus a protocol for treatment of
metastatic spinal disease [23, 24]. They took a
series of 31 magnetic resonance imaging studies
across 27 patients to dene these patterns prior
to suggesting the said criteria and subsequent
protocol.
Observationally, they identied four stages of
vertebral body deformity in the setting of metastatic disease. These stages accounted for percentage of body involvement as well as the degree of
body deformity compared to adjacent, unaffected
levels. Type I is assigned to vertebral bodies
with a degree of involvement or complete body
involvement but without any collapse (IA and IB,
respectively). Type II demonstrates endplate collapse on either one (IIA) or both (IIB) ends of the
body, again associated with the degree of marrow
replacement. Type III represents end- stage collapse with complete bony destruction. These are
subcategorized into those with kyphotic collapse
(IIIA) and symmetric collapse (IIIB). Finally,
Type IV is described to represent those with
translational deformity due to collapse. In each of
the ve patients studied with this deformity, there
was associated posterior element involvement of
the disease process (Fig.5.5).
These stages were then grouped into a classication system for instability as follows:
Impending axial instability: Type IA or IB
Axial instability: Type II or III
Impending translational instability: Type II or III
with posterior element involvement
Translational instability: Type IV
Finally, each class in the system was assigned
a treatment recommendation by the authors:
Impending axial instability without canal com-
promise: Radiation/chemotherapy
Impending axial instability with canal compro-
mise: Radiation/chemotherapy and surgical
decompression if radioresistant
T
T
T
T
5 Spinal Instability inMetastatic Disease
Fig. 5.5 Four stages of
vertebral body collapse as
dened by Asdourian etal.
From Asdourian PL, Mardjetko
S, Rauschning W, Jónsson H Jr,
Hammerberg KW, Dewald RL,
An Evaluation of Spinal
Deformity in Metastatic Breast
Cancer, Clin Spine Surg, 1990,
Jan 1;3(2)
ype IA
61
Type IB
ype IIA
ype IIIA
Type IIB
Type IIIB
(cervical)
ype IV
Type IIIB
(lumbar)
Axial instability: Anterior surgical stabilization if
single level, posterior if multilevel
Impending translational instability: Anterior ver-
sus anterior/posterior stabilization
Translational instability: Posterior stabilization
with posterolateral or anterior decompression
physiologic loads, protecting against initial or
additional neurologic decits, major deformity,
and incapacitating pain [2].
Initially, their work exploring the biomechanical properties of cadaveric cervical spine models
provided great insight into the passive restraints to
supraphysiologic motion [25–27]. They sequentially sectioned specimens in a controlled fashion,
White andPanjabi
rst in an anterior to posterior method followed by
independent specimens from posterior to anterior.
The conclusive denition of spinal instability
was provided by White and Panjabi in 1990 as
they outlined a series of evaluation criteria as a
“checklist” for instability. They stated that clinical instability was the loss of the spine’s ability to
maintain normal patterns of displacement under
These sections were then subjected to deforming
forces and the displacement was measured. Their
suggestion after the review of their own results was
that stability was an entity dened solely by osseous and ligamentous restraints and did not rely on
active management by cervical musculature [28].
62
J. C. Patt and D. P. Leas
Additionally, they were able to cement the concept
that anterior structures restrained extension forces,
while posterior structures were tethers to exion.
In total, the understanding offered by this
detailed look at the passive biomechanics in spinal
stability paved the way for creating the lower
cervical and lumbar spine checklists [2, 29]. In
each case, a cumulative score of ve points is
enough to have a high clinical suspicion of segmental instability of the spine (Tables 5.1 and 5.2).
Table 5.1 Lumbar spine checklist
Element
Anterior elements destroyed or unable to function
Posterior elements destroyed or unable to function
Radiographic criteria
Flexion-extension radiographs
Sagittal plane translation > 4.5mm or 15% 2
Sagittal plane rotation
15 at L1-2, L2-3, and L3-4 2
20 at L4-5 2
25 at L5-S1 2
Resting radiographs
Sagittal plane displacement >4.5mm or 15% 2
Relative sagittal plane angulation >22° 2
Cauda equina damage
Dangerous loading anticipated
From White A, Panjabi, M, Clinical Biomechanics of the Spine, 2nd ed., Wolters Kluwer, 1990
2
2
4
3
1
Table 5.2 Cervical spine checklist
Element
Anterior elements destroyed or unable to function
Posterior elements destroyed or unable to function
Positive stretch test
Radiographic criteria
Flexion-extension radiographs
Sagittal plane translation > 3.5mm or 20% 2
Sagittal plane rotation > 20° 2
Resting radiographs
Sagittal plane displacement >3.5mm or 20% 2
Relative sagittal plane angulation >11° 2
Abnormal disc narrowing
Developmentally narrow spinal canal
Sagittal diameter < 13mm 1
Pavlov’s ratio > 0.8 1
Spinal cord damage
Nerve root damage
Dangerous loading anticipated
2
2
2
4
1
2
1
1
Reproduced with permission from: White AA III, Panjabi MM: Update on the Evaluation of Instability of the
Lower Cervical Spine, in: Grin PP (ed): Instructional Course Lectures 36. Rosemont, IL, American Academy
of Orthopaedic Surgeons, 1987, pp513–520
5 Spinal Instability inMetastatic Disease
63
The editor applies White and Panjabi’s denition
of physiologic instability to help determine whether
a patient has spinal instability that may warrant stabilization. A clinical example of the utility of this
denition compared to Asdourian and SINS is the
example of symmetric, end stage vertebral body
collapse. Asdourian and SINS would consider this
an unstable spine. However, the editor has treated
many patients with this presentation who did not
demonstrate physiologic instability with progressive deformity, progressive neurologic dysfunction,
or pain recalcitrant to medical management. These
patients remained stable after radiation therapy and
corticosteroids. We have seen a couple patients with
complete vertebral body collapse and facet incongruity or diastasis who did demonstrate physiologic
instability. The editor believes that the White and
Panjabi denition of physiologic instability is helpful to determine spinal instability.
SINS
In 2010, the Spine Oncology Study Group released
a comprehensive review of the available literature,
combined with their own professional experience,
using the Delphi technique of assessing member’s
opinions on the relevant factors associated with
instability in the setting of an oncologic process.
These serial opinions were then adapted in tandem
with the existing literature base to create the Spinal
Instability Neoplastic Score (SINS) [30].
Variables including character of pain, disease
location, and descriptors of bony involvement
were presented before the study group, and a relative scoring system was then adapted as follows
in Table5.3.
The SINS system notably includes many characteristics from previous classication systems
covered and assigned relative scores to each category to help weight associated symptoms appropriately. As patients progressed with higher and
higher scores, the increased risk of instability is
immediately understood.
As a conclusion to their outlined scoring
system, the authors provided insight into what
numerical score denoted concern for instability
in the hope that oncologists and surgeons alike
Table 5.3 Spinal Instability Neoplastic Score (SINS)
Element Score
Location
Junctional (occiput–C1,
C7–T2, T11–L1, L5–S1
Mobile
spine (C3–C6, L2–L4)
Semirigid (T3–T10) 1
Rigid (S2–S5) 0
Pain relief with recumbency and/or pain with
movement/loading of the spine
Yes 3
No (occasional pain but not
mechanical)
Pain-free lesion 0
Bone lesion
Lytic 2
Mixed (lytic/blastic) 1
Blastic 0
Radiographic spinal alignment
Subluxation/translation
present
De novo deformity
(kyphosis/scoliosis)
Normal alignment 0
Vertebral body collapse
>50% collapse 3
<50% collapse 2
No collapse with >50%
body involved
None of the above 0
Posterolateral involvement of the spinal
elements
(Facet, pedicle, or CV joint
fracture or replacement with
tumor)
Bilateral 3
Unilateral 1
None of the above 0
3
2
1
4
2
1
would have guidance on the next step of treatment.
For patients with a score from 0 to 6, the authors
suggested that these were likely “stable” spines
and could be managed nonoperatively from the
perspective of stability. Consultation with a spine
surgeon was not necessary, and systemic and/or
radiation therapy could be considered. With a
score of 7–12, patients were categorized as indeterminate instability, and any score greater than 7
merited surgical consultation. Finally, scores of
13–18 denoted instability, and intervention was
likely necessary if the patient was deemed a reasonable surgical candidate.
64
J. C. Patt and D. P. Leas
When considering the SINS scoring system,
it is important to note at this point that while
patients may start at one end numerically, progressive disease processes may move their
score up with time and they should be monitored for these changes. Additionally, this scoring system is one dened around stability at a
single level and does not account for discontinuous lesions nor does it account for neurologic
symptoms.
The study group went on to provide a clinical
validation in 2011 where 30 patients were presented to the members of the study group individually [31]. Scoring of each subcategory and
the nal categorization of stable, potentially
unstable, and unstable were analyzed and interand intra-observer reliability calculated. There
was near-perfect correlation of the total SINS
score with an inter- and intra-observer reliability
of 0.846 and 0.886, respectively. The sensitivity
and specicity of the SINS scoring system were
demonstrated to be 95.7 and 79.5%, respectively.
Additionally, and perhaps most importantly, no
“unstable” were grouped into the “stable”
category.
Separate evaluations and validations were
performed using the SINS system. A validation
was performed in radiation oncologists where
they found substantial interobserver and excellent intra-observer reliability between providers. And again, most importantly, there were no
cases of an unstable spine being categorized as
“stable” by the providers [32]. A separate evaluation by oncologists noted the gradual decrease
in the mean SINS score for patients, positing
that an increased awareness of relevant clinical
criteria provided an earlier diagnosis of risk factors for instability and appropriate referral [33].
Galasko etal. highlighted a signicant need for
education of potential referring providers after
identifying that many patients present to their
clinic in a delayed fashion despite symptoms of
instability [34].
Conclusions
Instability of the spine from metastatic disease
is difcult to quantify, but there are a number
of systems that have been designed to assist
the clinician to appropriately stratify their
patient’s risks and direct them toward the most
appropriate treatment pathway.
Fundamental components of patient care,
such as a thorough history and physical examination, remain at the foundation of diagnosis
and treatment. Decision-making can be supported by routine and advanced imaging studies, conrming the clinical impression.
Baseline imaging studies with plain radiographs should always be obtained to allow for
longitudinal evaluation of disease processes
and progression, particularly as more advance
imaging modalities are both costly and less
convenient for routine follow-up. However, the
advanced studies of CT and MR imaging
should be part of the initial workup to help better understand the disease process that each
patient faces.
The Cancer Center at Memorial Sloan
Kettering uses a combination of clinical and
pathologic criteria to assist with determining the
treatment pathway for spinal neoplastic processes. One of their most important contributions is the neurologic, oncologic, mechanical,
and systemic (NOMS) decision framework.
This framework importantly includes the
mechanical impact of spinal neoplasms when
determining treatment pathways, and a thorough understanding of instability is a critical
step in providing excellent care for our patients
[35] (Fig.5.6).
There are many systems which can assist
the clinician with clinical decision-making
and help us to provide our patients with an
understanding of their individual risk of
instability and potential morbidity from
intrinsic spinal instability due to neoplastic
disease (both benign and malignant).
Depending on the clinical scenario, components of multiple systems may need to be
employed, so a thorough understanding of
these concepts is essential for the clinician.
This understanding of risk can be translated
to the bedside to help determine the potential
surgical and nonsurgical treatment options
best suited to the individual patient’s stage of
disease.
Systemic
5 Spinal Instability inMetastatic Disease
Low-grade ESCC
No myelopathy
65
Radiation
High-grade ESCC
+/− myelopathy
Radiosensitive
Radioresistant/
previously radiated
Stable
Mechanical Oncologic Neurologic
Unstable
Able to tolerate
surgery
Unable to tolerate
surgery
Fig. 5.6 Neurologic, oncologic, mechanical, and sys-
temic decision framework by Memorial Sloan Kettering
(2013). Republished with permission from John Wiley
and Sons, from Laufer I, Rubin DG, Lis E, Cox BW,
Stubbleeld MD, Yamada Y, Bilsky MH, The NOMS
cEBRT
SRS
Separation surgery
Stabilization
framework: approach to the treatment of spinal metastatic
tumors, Oncologist, 2013 Jun;18(6):744–51, doi: 10.1634/
theoncologist.2012-0293, epub 2013 May 24, permission
conveyed through Copyright Clearance Center, Inc.
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