Download Anatomy and Blood Supply of the Sternum

7
Anatomy and Blood Supply
of the Sternum
Winfried Neuhuber, Stefan Lyer, Christoph Alexiou, and Thomas Buder
2.1
Bony Anatomy – 8
2.2
Relationship to Muscles – 8
2.3
Development – 9
2.4
Arterial Supply – 10
References – 11
R. E. Horch et al. (Eds.), Deep Sternal Wound Infections,
DOI 10.1007/978-3-662-49766-1_2, © Springer-Verlag GmbH Deutschland 2017
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Chapter 2 · Anatomy and Blood Supply of the Sternum
2.1
Bony Anatomy
The sternum is a sword-shaped flat bone about
­15–17 cm long in the adult (. Fig. 2.1) (Putz and
Müller-Gerbi Benninghoff 2003; Williams and
Warwick 1980). Its cranial part, the manubrium,
connects to the corpus by a synchondrosis in 90% of
adults; in the remaining 10% there is a bony fusion
(synostosis). Its caudal part, the xiphoid process, is
cartilaginous in youth, but more or less ossified and
fused with the corpus in adults. The sternum is
slightly convex ventrally emphasized by the individually variable sternal angle (. Fig. 2.1). The clavicle and the cartilage of the first rib articulate on the
lateral margin of the manubrium while the cartilages of ribs two through seven insert from the manubrium–corpus connection caudalward on the
lateral edge of the corpus, partly by true synovial
joints. These articulations correspond to the borders between the primitive segments of the developing sternum, the so-called sternebrae. Sternocostal
ligaments arranged criss-cross ventrally and dorsally connect the sternum with the rib cartilages,
fusing with both their periosteum and perichondrium, respectively, thus forming a rather firm
membrane especially on the ventral side. The cortical bone of the sternum is thickest in the manu­
brium but relatively thin in the other parts. The
spongiosa is lightly constructed with wide inter­
trabecular spaces containing red bone marrow
(. Fig. 2.2) (Whitehouse 1975).
2.2
..Fig. 2.1 Anterior view of a macerated adult sternum.
­Costal cartilages were modeled of plastic. The manubrium
(M) is connected to the corpus (C) by cartilage at the sternal
angle (red arrow). Black arrows point to transverse ridges
­indicating the fusion lines between the sternebrae. Percentages indicate the relative prevalence of collateral sternal
rami from the first to the sixth intercostal spaces. Xiphoid
process (X)
Relationship to Muscles
Ventrally, the sternum provides attachment to the
sternal portion of the pectoralis major, dorsally to
the transversus thoracis. The xiphoid process provides attachment to the aponeuroses of the oblique
and transverse abdominal muscles and the sheath of
the rectus abdominis formed by them; the linea alba
is attached to its apex. From its dorsal aspect originates the sternal portion of the diaphragm. A sternal
muscle is found in about 3% of cases on the ventral
side of the sternum (Testut 1884).
..Fig. 2.2 Midsaggital section through the sternum emphasizing the cortical bone and spongiosa. In this case, the
manubrium is fused to the corpus by synostosis
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2.3 · Development
2.3
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Development
The sternum develops from bilateral paramedian
cartilaginous sternal plates that interconnect the
costal anlagen. Upon their midline fusion in early
fetal life, several ossification centers emerge that
form the manubrium and four bony plates in the
region of the corpus, the sternebrae (. Fig. 2.3).
They fuse during adolescence, while the connection
between the manubrium and corpus remains cartilaginous in the great majority of adults (. Fig. 2.1).
Transverse ridges on the anterior surface of the
adult sternum indicate the fusion lines. The second
through sixth or seventh ribs insert at these lines,
and thus the intersegmental position of the sternebrae is evident. As the arterial supply of the developing sternum is directed to the ossification centers of
the sternebrae, an intersegmental pattern of arterial
branches to the sternum (rami sternales) is defined
(. Fig. 2.3, . Fig. 2.4) (Putz and Müller-Gerbi 2003;
Williams and Warwick 1980).
a
..Fig. 2.3 Posterior view of an infant sternum with attached ribs. The large ossification center on top will form the
manubrium, the four smaller will form the sternebrae of the
corpus. Red arrows indicate the intersegmental arteries to
ossification centers. ITA internal thoracic artery and vein,
MPHA musculophrenic artery. Historic specimen, late eighteenth century. (Courtesy of Anatomy Collection of the Institute of Anatomy, University of Erlangen-Nürnberg)
b
..Fig. 2.4 Three-dimensional reconstruction of a postmortem computed tomographic digital subtraction angiography of
the internal thoracic artery (ITA) of an 80-year-old female body donor. Iodine contrast agent (Imeron 350, Bracco Altana
­Pharma, Konstanz, Germany, diluted 1:1 with 0.9% NaCl, 175 mg/ml iodine) was injected manually into the right artery (RITA)
filling its various ipsilateral branches but also the left artery (LITA) via a commissural vessel (comm) behind the apex of the
sternum. Note that the main trunks of the RITA and LITA, the sternal (rs) and intercostal (ic) branches, as well as the commissural and musculophrenic (MPHA) arteries are better visualized in the oblique left posterior (b) than in the oblique left anterior (a) view that emphasizes perforating branches (perf). Data were created using a C-arm cone beam computed tomographic
scanner (Siemens Artis zee floor, Siemens Healthcare, Forchheim, Germany). Three-dimensional reconstruction of arteries
and skeletal structures in an 8-cm-thick slice volume was achieved using special software (MultiModality Workplace, Siemens
Healthcare, Forchheim, Germany)
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Chapter 2 · Anatomy and Blood Supply of the Sternum
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a
b
c
d
..Fig. 2.5 Scheme of noncollateral (a) and three types of collateral (b, c, d) sternal rami. In a, the three main branches of the
ITA, i.e., the sternal (st), anterior intercostal (ant intercost), and perforating (perf), are depicted as originating separately from
the internal thoracic artery (ITA). If the common trunk in b (sternal/intercostal type) is ligated, the collateral sternal circulation is maintained from the posterior intercostal artery (post intercost) via the anterior intercostal ramus. In the sternal/perforating type, the collateral supply of the sternum (ST) in the case of ligation is established from branches of lateral thoracic
and/or acromiothoracic arteries in the pectoral muscle (PM) or overlying skin via the perforating branch of the ITA that
shares its origin with the sternal ramus. In d, all three branches share a common origin from the ITA. In this sternal/perforating/intercostal type, sources of collateral circulation may be both lateral thoracic/acromiothoracic and posterior intercostal
arteries anastomosing with perforating or anterior intercostal rami, respectively. Dashed line indicates the periosteal plexus
2.4
Arterial Supply
Detailed studies of the arteries to the sternum have
been repeatedly performed over the past four decades prompted by the notorious complications in
sternotomy wound healing, particularly if the internal thoracic artery was harvested for coronary bypass. Both anatomical dissection on large series of
donated bodies and radiography techniques were
used.
The major source of branches to the sternum is
the internal thoracic or mammary artery (ITA)
(. Fig. 2.3, . Fig. 2.4). It originates from the subclavian artery directly or sometimes from a common
trunk with another artery of the thyrocervical
trunk; this was observed in about 30% of cases on
the left but rarely on the right side (Henriquez-Pino
et al. 1997; Paliouras et al. 2015). Before entering the
mediastinum, it crosses the phrenic nerve either
dorsally or ventrally (Owens et al. 1994; Rigaud et
al. 1998). This may explain diaphragmatic dys­
function upon open heart surgery (Abd et al. 1989;
Owens et al. 1994; Wilcox et al. 1990). It descends
1–2 cm from the lateral margin of the sternum
­adjacent to the posterior aspect of the chest wall,
partly covered by the transversus thoracic muscle
from the third to the sixth costal cartilage. After
­giving off the musculophrenic artery (. Fig. 2.3,
. Fig. 2.4) and passing the level of the diaphragm
anterior to the sternocostal triangle (Morgagni’s triangle, often erroneously named after Larrey), the
ITA enters the sheath of the rectus abdominis, now
termed the superior epigastric artery, and anastomoses with the inferior epigastric artery.
Branches to the sternum originate either directly from the medial aspect of the ITA (noncollateral
branches) or from short (0.5–8.0 mm) trunks that
also give rise to perforating branches to the intercos-
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References
tal and pectoral muscles and overlying skin or to
anterior intercostal rami (collateral branches;
Berdajs et al. 2006; de Jesus and Acland 1995; Pietrasik et al. 1999) (. Fig. 2.4, . Fig. 2.5). They are very
small (range of diameters 0.30–0.92 mm: Gupta et
al. 2002; Pietrasik et al. 1999; 0.2–1.6 mm: de Jesus
and Acland 1995), run at a distance of less than
5 mm from the sternal edge in almost half of the
individuals (de Jesus and Acland 1995), and display
considerable interindividual and gender (Itezerote
et al. 2012) variability. This is also reflected by the
slightly differing descriptions and schematic representations in the various studies. However, two consistent patterns emerged. First, sternal branches are
intersegmental, i.e., located in the intercostal spaces
and form arcades at the lateral edge of the sternum
(Berdajs et al. 2006; Rigaud et al. 1998). This reflects
the intersegmental location of ossification centers
that are supplied by sternal arteries (Pis’menov and
Zapetskii 1977). Second, sternal branches are more
frequent in cranial than in caudal segments, in particular in the second and third intercostal space,
with some caudal spaces even without any artery (de
Jesus and Acland 1995; Gupta et al. 2002; Itezerote
et al. 2012). Eighty-six percent of collateral vessels
were found in the first to fourth intercostal spaces
while only 14% occurred in the fifth and sixth
­spaces (de Jesus and Acland 1995).
Noncollateral sternal branches are more numerous than collateral ones. de Jesus and Acland (1995)
reported an average of five noncollateral versus one
to three collateral branches, depending on the type,
per hemisternum. In the study of Berdajs et al.
(2006) of 50 donated bodies, a total of 22 noncollateral branches versus 8 to 17 collateral ones, again
depending on type, were described. This highlights
the generally precarious arterial supply to the sternum. Based on the origins of the collateral sternal
branches, three typical patterns can be defined
(. Fig. 2.5): sternal/intercostal (from the anterior
intercostal rami of the ITA; collateral supply via an
anastomosis between the posterior intercostal arteries and anterior intercostal rami), sternal/perforating (from the perforating rami of the ITA; collateral
supply via an anastomosis between the perforating
rami and branches of acromiothoracic and/or lateral thoracic arteries: Berdajs et al. 2006; de Jesus
and Acland 1995; Palmer and Taylor 1986; Reid and
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Taylor 1984) and sternal/perforating/intercostal
(both sternal and anterior intercostal rami originate
from a perforating branch; Berdajs et al. 2006;­
de Jesus and Acland 1995; Itezerote et al. 2012;
­Pietrasik et al. 1999). A particular rare type is the
persistent posterior intercostal artery that reaches
the sternum without anastomosing with the ITA (de
Jesus and Acland 1995; Itezerote et al. 2012). In
some individuals, a commissural anastomosis
­between both ITAs can be found (. Fig. 2.4).
Arteries reach the anterior and posterior aspects
of the sternum, feeding into dense periosteal plexuses, which are better developed on the posterior
side (. Fig. 2.4). The plexuses are segmentally organized in infants, corresponding to sternebrae, but
are confluent craniocaudally in adults (Pis’menov
and Zapetskii 1977). They are apparently also
c­ontinuous across the midline as the contralateral
ITA fills with contrast medium injected into the ipsilateral ITA (Rigaud et al. 1998; . Fig. 2.4).
Evidently, harvesting the ITA for coronary bypass will disrupt sternal circulation to a variable extent (Seyfer et al. 1988), although this hypoperfusion
may be temporary in most cases (Carrier et al. 1992).
This depends on the number and viability of the altogether rare collateral sternal rami and their access
to the periosteal plexus of the sternum. Thus, when
the ITA is dissected, any branches should be ligated
as close as possible to the main vessel in order to preserve collateral branches. Likewise, sternal cerclages
should be placed as close as possible to the sternal
edge to preserve the arcades between sternal arteries
(de Jesus and Acland 1995; Berdajs et al. 2006).
jjAcknowledgments
We thank Philip Eichhorn for photographical documentation.
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Chapter 2 · Anatomy and Blood Supply of the Sternum
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