Sternal metastasis - the forgotten column and its effect on thoracic spine stability

Abstract

Sternal metastases are not studied extensively in the literature. There is a paucity of information on their role in metastatic disease. The concept of the fourth column was described by Berg in 1993, and has been proven in case report, clinically and biomechanical studies. The role of the sternum as a support to the thoracic spine is well documented in the trauma patients, but not much is known about its role in cancer patients. This review examines what is known on the role of the fourth column. Following this we have identified two likely scenarios that sternal metastases may impact management: (1) sternal pathological fracture increases the mobility of the semi-rigid thorax with the loss of the biomechanical support of the sternum-rib-thoracic spine complex; and (2) a sternal metastasis increases the risk of fracture, and while being medical treated the thoracic spine should be monitored for acute kyphosis and neurological injury secondarily to the insufficiency of the fourth column.

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World Journal of
Orthopedics
World J Orthop 2017 June 18; 8(6): 441-523
ISSN 2218-5836 (online)

Contents Monthly Volume 8 Number 6 June 18, 2017
I June 18, 2017
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REVIEW
441 Perioperative blood management strategies for patients undergoing total knee replacement: Where do we
stand now?
Themistoklis T, Theodosia V, Konstantinos K, Georgios DI
MINIREVIEWS
455 Sternal metastasis - the forgotten column and its effect on thoracic spine stability
Piggott RP, Curtin M, Munigangaiah S, Jadaan M, McCabe JP, Devitt A
461 Role of fetuin A in the diagnosis and treatment of joint arthritis
Pappa E, Perrea DS, Pneumaticos S, Nikolaou VS
ORIGINAL ARTICLE
Retrospective Study
465 Emergent reintubation following elective cervical surgery: A case series
Schroeder J, Salzmann SN, Hughes AP, Beckman JD, Shue J, Girardi FP
471 Two-stage surgical treatment for septic non-union of the forearm
Perna F, Pilla F, Nanni M, Berti L, Lullini G, Traina F, Faldini C
Observational Study
478 Upper extremity disorders in heavy industry workers in Greece
Tsouvaltzidou T, Alexopoulos E, Fragkakis I, Jelastopulu E
484 Medial tibial plateau morphology and stress fracture location: A magnetic resonance imaging study
Yukata K, Yamanaka I, Ueda Y, Nakai S, Ogasa H, Oishi Y, Hamawaki J
SYSTEMATIC REVIEWS
491 Clinical application of concentrated bone marrow aspirate in orthopaedics: A systematic review
Gianakos AL, Sun L, Patel JN, Adams DM, Liporace FA
507 Distal triceps injuries (including snapping triceps): A systematic review of the literature
Shuttlewood K, Beazley J, Smith CD
514 Worldwide orthopaedic research activity 2010-2014: Publication rates in the top 15 orthopaedic journals
related to population size and gross domestic product
Hohmann E, Glatt V, Tetsworth K

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I-III Editorial Board
Contents
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World Journal of Orthopedics
Volume 8 Number 6 June 18, 2017
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AIM AND SCOPE
INDEXING/ABSTRACTING
FLYLEAF

Robert Pearse Piggott, Mark Curtin, Sudarshan Munigangaiah, Mutaz Jadaan, John Patrick McCabe,
Aiden Devitt
MINIREVIEWS
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Sternal metastasis - the forgotten column and its effect on
thoracic spine stability
Robert Pearse Piggott, Mark Curtin, Sudarshan Munigan-
gaiah, Mutaz Jadaan, John Patrick McCabe, Aiden Devitt,
Department of Trauma and Orthopaedic Surgery, Galway
University Hospitals, the West/North West Hospitals Group,
HSE, Galway H91 YR71, Ireland
Author contributions: All authors equally contributed to this
paper with conception and design of the study, literature review
and analysis, drafting and critical revision and editing, and nal
approval of the nal version.
Conflict-of-interest statement: Regarding the paper entitled
“Sternal Metastasis - the forgotten column and its effect on
thoracic spine stability”; the authors do not report any conict of
interest.
Open-Access: This article is an open-access article which was
selected by an in-house editor and fully peer-reviewed by external
reviewers. It is distributed in accordance with the Creative
Commons Attribution Non Commercial (CC BY-NC 4.0) license,
which permits others to distribute, remix, adapt, build upon this
work non-commercially, and license their derivative works on
different terms, provided the original work is properly cited and
the use is non-commercial. See: http://creativecommons.org/
licenses/by-nc/4.0/
Manuscript source: Unsolicited manuscript
Correspondence to: Robert Pearse Piggott, Orthopaedic
Specialist Registrar, Department of Trauma and Orthopaedic
Surgery, Galway University Hospitals, the West/North West
Hospitals Group, HSE, Newcastle Road, Galway H91 YR71,
Ireland. robpiggott1@gmail.com
Telephone: +353-091-544000
Received: December 13, 2016
Peer-review started: December 16, 2016
First decision: March 27, 2017
Revised: April 1, 2017
Accepted: April 23, 2017
Article in press: April 24, 2017
Published online: June 18, 2017
Abstract
Sternal metastases are not studied extensively in the
literature. There is a paucity of information on their role
in metastatic disease. The concept of the fourth column
was described by Berg in 1993, and has been proven
in case report, clinically and biomechanical studies. The
role of the sternum as a support to the thoracic spine is
well documented in the trauma patients, but not much
is known about its role in cancer patients. This review
examines what is known on the role of the fourth column.
Following this we have identied two likely scenarios that
sternal metastases may impact management: (1) sternal
pathological fracture increases the mobility of the semi-
rigid thorax with the loss of the biomechanical support of
the sternum-rib-thoracic spine complex; and (2) a sternal
metastasis increases the risk of fracture, and while being
medical treated the thoracic spine should be monitored
for acute kyphosis and neurological injury secondarily to
the insufciency of the fourth column.
Key words: Fourth column; Sternal fracture; Sternal
metastasis; Sternal-rib-thoracic spine complex; Spine
stability
© The Author(s) 2017. Published by Baishideng Publishing
Group Inc. All rights reserved.
Core tip: The sternal-rib complex provides additional
support to the thoracic spine. The role of sternal fracture
affecting the stability of the thoracic spine is well established
in trauma, to date however its role in metastatic disease is
unclear. Biomechanical studies highlight its importance and
the presence of sternal metastasis should be considered
when assessing the stability of the thoracic spine in
metastatic disease.
Piggott RP, Curtin M, Munigangaiah S, Jadaan M, McCabe JP,
Devitt A. Sternal metastasis - the forgotten column and its effect
Submit a Manuscript: http://www.f6publishing.com
DOI: 10.5312/wjo.v8.i6.455
World J Orthop 2017 June 18; 8(6): 455-460
ISSN 2218-5836 (online)

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Piggott RP
et al
. Sternal metastasis and spinal stability
on thoracic spine stability. World J Orthop
2017; 8(6): 455-460
Available from: URL: http://www.wjgnet.com/2218-5836/full/
v8/i6/455.htm DOI: http://dx.doi.org/10.5312/wjo.v8.i6.455
INTRODUCTION
Cancer remains the second leading cause of death in the
United States, with 589430 cancer related deaths each
year[1]. In Europe, collective data from 40 countries has
yielded an annual incidence of 3.45 million new cases per
year, with 1.75 million cancer related deaths[2]. With early
detection and increased treatment options, prolonged
survival in patients with metastatic disease will result
with increased incidence of skeletal related events (SREs)
that will require orthopaedic intervention. The skeleton
is the third most common site for metastatic disease to
occur in the body, with only the lungs and liver with a
higher incidence. Within the skeletal system, the spine
is the most common site of metastases. The thoracic
spine is most prone to metastatic disease as it contains
the greatest volume of bone marrow per vertebrae[3].
Bone metastases are associated with a considerable
degree of morbidity both due to pain and SREs. SREs
are dened as a pathological fracture, a requirement for
surgical intervention and palliative radiotherapy to a bone
lesion, hypercalceamia of malignancy, and spinal cord
compression. Metastatic spinal cord compression occurs
in 3.4% patients with cancer per year in the United
States[4] is a source of considerable morbidity. Breast,
prostate, renal, lung, and haematopoietic tumours most
commonly metastases to the spine and are discussed
elsewhere in more detail. But what of sternal metastases
which occur in the setting of spinal metastatic disease.
Do they have an effect on the spine and its stability?
Sternal metastases are a rare phenomenon[5,6] and
there is a paucity of information published regarding their
incidence and also their effect on spine stability. Best
medical therapy, such as external beam radiotherapy
or chemotherapy, is advocated for the vast majority of
cases[7] however when a pathological fracture occurs, then
there is potential for delayed union and deformity. When
present with concomitant thoracic spinal disease then the
role of the sternum-rib-thoracic spine complex in thoracic
spine stability, as the fourth column, is an important
consideration. Berg[8] rst proposed the fourth column in
1993, as an adjunct to the three-column theory of spine
stability of Denis[9]. To date no study has looked at the role
of the sternum in thoracic spine stability in the presence of
a sternal metastasis. Hence the focus of this review is to
identify what is known on the topic of sternal metastasis in
the setting of spinal metastatic disease, and their potential
effect on spine stability.
STERNAL METASTASES - WHAT IS
KNOWN?
There has been little focus on the incidence and
association of sternal metastatic disease in recent years. A
necropsy study by Urovitz et al[5] form 1977 remains the
largest single study on the topic. In a patient population
of 415 patients, the incidence of sternal metastases
was found to be 15.1%, of which 30.2% had a sternal
fracture[5]. These fractures also demonstrated delayed
or nonunion features and were associated with greater
deformity than traumatic sternal fractures[5]. Conicting
reports on the commonest location and most prevalent
tumours exist. Urovitz et al[5] identied the body of the
sternum as the commonest site of metastases with
breast, lymphoma and myeloma the most prevalent
primary oncological processes. This was contrary to
what was previously described by Kinsella et al[6] who
concluded that the manubrium was most at risk, and
that thyroid, renal and breast carcinoma were the most
common. These ndings are summarized in Figure 1.
Once sternal metastases have developed, best
medical therapy with either radiotherapy, hormonal
therapy or chemotherapy is recommended as per the
primary diagnosis[7]. This is regardless of location and
size of the metastatic disease as the sternum is a non-
weight bearing bone and treatment is not altered by
whether the lesion is osteoblastic, osteolytic or mixed
on imaging[7]. The treating oncologist should closely
evaluate the response of treatment, especially pain
relief. If pathological fracture occurs, continued medical
therapy is advocated and only those patients who fail
best medical therapy are to be referred for consideration
for surgical intervention[7]. Sternal metastasis in isolation
may be treated by a number of mechanisms. Usually in
the setting of isolated metastatic disease, the tumour
may be excised and the sternum may be reconstructed
with titanium mesh[10], locking titanium plate[11] or even
an allogenic transplant[12]. In the palliative setting,
kyphoplasty of sternal metastasis has been advocated
for pain relief[13]. Unfortunately, all recommendations
are for sternal metastases in isolation and do not take
into account the sternum-rib-thoracic spine complex in
combination. Specically, there are no recommendations
for the prophylactic surgery on the sternum to prevent
fracture in a patient with concurrent spinal metastatic
disease.
SPINAL METASTASIS
Spinal metastases can be treated medically, with
radiotherapy and or spinal surgery and treatment must
be individualized to accommodate for tumour type,
performance status of the patient, life expectancy and
neurological status. It is a fundamental realization that any
intervention with regards spinal metastases is palliative.
There are four primary indications to intervening in
metastatic disease of the spine: Neurological compromise,
spinal instability, unrelenting pain and in the case which
histological diagnosis must be established. Historically
radiotherapy became the first-line treatment for most
patients[14]. Recent advances in imaging, surgical tech-
nique and instrumentation systems have improved

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outcomes from surgery. Patchell et al[15] in a randomized
control trial showed that surgery follow by radiotherapy
to be superior to radiotherapy alone. These findings
were reproduced in a large multicentre observational
study[16]. The is a multitude of evidence on surgery in
neurological compromise including spinal cord compression,
in which cases the spine needs to be decompressed
and stabilized[17-19]. The sternum in this setting does not
play a role in the management strategy as the evidence
supports intervention regardless of sternal disease.
Likewise, management of intractable pain and the need
for histological diagnosis is not altered by whether disease
is present in the sternum. Spinal stability however is
directly affected by the sternum in biomechanical studies
of the spine[20] and thus it follows that it has the potential
to affect stability in the metastatic spine, but remains to be
investigated fully.
STABILITY WITH SPINAL METASTASIS
Assessing the spine stability in metastatic disease how-
ever is more difficult, and especially in the setting of
impending instability, the sternum could play a role. Form
the literature we know that defining instability in the
spine using trauma criteria is not directly applicable to the
setting of metastatic disease[21]. This is because the injury
does not follow typical patterns seen in trauma, and
involves different biological healing potential and patient
factors[22]. As we have no evidence on the topic then
we must be cautious when applying observations from
traumatic sternal and spinal injuries to the oncological
setting as we assess the thoracic spine as a whole with
the sternum-rib-thoracic spine complex.
The Spine Oncology Study Group (SOSG) defines
stability as the “loss of spinal integrity as a result of a
neoplastic process that is associated with movement-
related pain, symptomatic or progressive stability and/or
neurological compromise under physiological loads”[22].
It is the major goal of any spinal surgery in oncology to
preserve or restore the spines stability. Regardless of
indication, surgery is generally reserved for patients with
a life expectancy of greater than 3 mo[23]. To determine
a patient’s life expectancy, multiple scoring systems
have been developed. Tokuhashi et al[24] developed
one example of a scoring system to evaluate prognosis
of metastatic spine tumour patients. This was further
assessed by Enkaoua et al[25] regarding its reliability, and
demonstrates a median survival of 5.7 mo with a score
≤ 7 mo vs 23.6 mo for a score of ≥ 8. Regardless of
scoring systems however, establishing survival of patients
is subjective and must take into account multiple patient
and disease factors before a decision on suitability for
surgery is made.
Surgeons rely on their clinical experience as well as
internationally accepted scoring systems to determine
a spines stability and appropriate treatment. The SOSG
have provided a classification n system for spinal
instability - The Spinal Instability Neoplastic Score (SINS)
- which was developed from existing evidence based
medicine and expert consensus opinion[22]. Factors
included in the score include location, pain, alignment,
vertebral body collapse, posterior element involvement
and type of bone lesion (Table 1). The SINS has been
shown to have good inter- and intraobserver reliability
in determining stability. Stability is derived from overall
score out of a max score of 18. Neoplastic disease is
Suprasternal notch
Manubrium
Clavicular notch
Sternal angle
Body
Urovitz
et al
[5]
Most common site
Most common primary
Breast
Lymphoma
Lung
Kinsella
et al
[6]
Most common site
Most common primary
Thyroid
Renal
Breast
Costal notches 2nd-7th
Xiphoid process
Figure 1 Sternum.
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deemed unstable with a score of 13-18, stable with a
score of 0-6 and indeterminate instability or possibly
impending with a score of 7-12. The specificity and
sensitivity of the SINS for unstable or potentially unstable
spines is 95.7% and 79.5% respectively. The SINS
provides a useful tool for assessing spinal disease and
aids in the decision making for surgical intervention but is
not binding. Unfortunately the sternum is not considered
in the SINS in its current format, and thus the fourth
column becomes the forgotten column when considering
spine stability in metastatic disease.
Further scoring systems exist which can also aid in the
decision making process. As survivorship improves with
neoplastic conditions so does the incidence of metastatic
disease in the axial skeleton. Predicting the survivorship
of patients with metastatic disease is important in the
planning of surgical intervention. The Oswestry Spinal
Risk Index (OSRI) is a simple, reproducible measure of
survivorship looking at primary tumor pathology and
the patient’s general condition[26]. It has been externally
validated twice and provides accurate prediction of a
patients survivorship which can be used in the decision
making process[27,28].
ROLE OF THE FOURTH COLUMN IN
METASTATIC DISEASE
Biomechanically, the inherent stability of the thoracic
spine is augmented by the sternum and rib cage, which
increases the moment of inertia and stiffens the spine
against rotary forces[29]. There is a multitude of evidence
from case reports, retrospective reviews and biomechanical
studies on the importance of the sternum and ribs in the
presence of thoracic spine injury in acute trauma but none
on metastatic disease. The association between sternal
fractures and spine injuries is well documented in the
literature[8,30-32]. In clinical practice a spinal injury must be
suspected to exist in the presence of a sternum fracture,
even at discordant levels.
A 50-year literature review by Fowler[30] concluded that
43% of sternum fractures had associated spinal fractures.
Berg postulated that the sternum and ribs represents a
fourth column of structural support for the thoracic spine
in addition to the three described by Denis[8]. The three
column model divides the osteoligamentous structures of
the spinal column into an anterior, middle and posterior
column[9]. Involvement of 2 of the 3 columns resulted
in potentially unstable spinal injury at risk of progressive
deformity and neurological compromise[9]. The additional
fourth column theory was based on two cases of displaced
sternal fractures with minimally displaced thoracic spine
injuries leading to progressive kyphosis[8].
This pattern of injury is often associated with neuro-
logical compromise, with increasing degrees of kyphosis
being observed. Golpalakrish and Masri reported 83% of
patients with sternum and spine fracture combinations
had complete neurologic injury and were paraplegic[32].
Vioreanu et al[31] in 2005 reported an incidence of 1.4%
of sternal fracture with vertebral fracture, which rises to
9.2% when the subset of thoracic fractures is examined
in isolation. There is a clear association of neurological
compromise in these patients with all six patients suffering
neurological injury of which four patients had complete
injuries[31].
However, neither Berg nor Vioreanu et al[31] described
the behavior of a three-column injury with an intact
sternum or “fourth column”. A case report by Shen
describes how the sternum provided sufficient stability
for the conservative management of a three-column
unstable injury pattern in an ankylosing spondylitis
patient without neurological compromise[33]. The authors
concluded that the case confirmed the existence and
clinical relevance of the fourth column proposed by
Berg. An in vitro cadaveric study estimated that the
sternum-rib complex accounts for up to 78% of thoracic
stability[34]. Watkins et al[20] examined the biomechanics
of the fourth column in 10 human cadaveric thoracic
spines using multidirectional exibility tests. They found
that an indirect flexion-compression fracture of the
sternum decreased the stability of the thoracic spine
by 42% in flexion-extension, 22% in lateral bending
and 15% in axial rotation[20]. This is evidence of the
importance of the sternum in stability of the thoracic
spine, and why the thoracic spine is considered a semi-
rigid structure[22]. Following from this we can conclude
that sternal and thoracic spine injury is a potentially
unstable combination.
Metastasis of the sternum and their role on stability
is not addressed in the Spinal Instability Neoplastic
Table 1 Spinal Instability Neoplastic Score
Score
Spine location
Junctional (occiput-C2, C7-T2, T11-L1, L5-S1) 3
Mobile (C3-C6, L2-L4) 2
Semi-rigid (T3-T10) 1
Rigid (S2-S5) 0
Mechanical or postural pain
Yes 3
No (occasional pain but not mechanical) 1
Pain-free lesion 0
Bone lesion quality
Lytic 2
Mixed lytic/blastic 1
Blastic 1
Radiographic spinal alignment
Subluxation/translation 4
De novo deformity (kyphosis/scoliosis) 1
Normal 0
Vertebral body involvement
> 50% collapse 3
< 50% collapse 2
No collapse with > 50% involvement 1
None of the above 0
Posterior involvement
Bilateral 3
Unilateral 1
None 0
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Score (Table 1). There are two areas where they have a
potential role, which needs to be further explored. The
thorax (T3-T10) is termed semi-rigid in the location score
secondary to the biomechanical benet of the sternum
and rib cage, and is only scored 1 out of a possible 3.
Concomitant sternal metastasis with pathological fracture
would affect the semi rigid nature of the thorax with
loss of the stability provided by the fourth column. The
flexion-extension stability of the spine is reduced by
42%[20] in this setting regardless of thoracic disease, with
rotational and lateral bending also affected. We must ask
the question - with the loss of the biomechanical benet
of the sternum, should the thoracic now be considered
“mobile” and the location score increased to 2 to reect
this? Secondarily, in the presence of metastases without
pathological fracture, a lytic lesion of the sternum would
be at risk for impeding fracture and should be observed
closely. If the spine is deemed stable, close follow up
of both the sternal and thoracic metastatic disease is
required as early de novo kyphosis deformity would
add an additional 2 points to a patients score and may
change management. The association between kyphosis
and loss of sternal integrity is well established in case
reports and carries a significant risk of neurological
injury[8,30,32].
In addition, sternal metastasis may be painful but
this would not impact on the SINS pain score. Local pain
may be related to the sternal metastases themselves but
back pain in the setting of concurrent sternum and spine
disease which worsens with movement and loading of
the spine and is relieved by recumbence would suggest
that it is mechanical in nature and thus increase the
patients score, as set out by the SOSG[22].
CONCLUSION
In conclusion, the thoracic spine should not be examined
in isolation. The sternum is a pivotal support in thoracic
spine stability and should not be overlooked when as-
sessing a patient’s thoracic spine. Assess spinal stability
in the metastatic diseased spine is a complex and mul-
tifactorial process. The sternum provides essential
support to the thorax spine and pathological fracture or
impending fracture in the sternum has the potential for
acute deformity of the thoracic spine that could lead to
neurological injury. No evidence exists on the sternum
role in metastatic spinal stability to date and thus hard
conclusions cannot be made. We recommend that sternal
metastatic disease be assessed in conjunction with spinal
metastatic disease, and that treatment be tailored to
individual cases. Further study is needed to fully evaluate
the role of the sternum in spine stability with metastatic
disease. A biomechanical study looking at the location
and involvement of the sternum and the subsequent
risk of fracture and deformity is needed to quantify the
risk to the spine. Following this there may be a role for
modification of the SINS once their role has been fully
investigated. For now, clinical judgment is recommended
until further evidence is provided in the literature.
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