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The intercostal space (Fig. 2.1)
space (also supplied by the main intercostal nerve).
Typically, each space contains three muscles comparable to those of
• Sensory branches from the pleura (upper nerves) and peritoneum
the abdominal wall. These include the:
(lower nerves).
• External intercostal: this muscle fills the intercostal space from the •A collateral branch which supplies the muscles of the intercostal
vertebra posteriorly to the costochondral junction anteriorly where it Exceptions include:
becomes the thin anterior intercostal membrane. The fibres run down- • The 1st intercostal nerve is joined to the brachial plexus and has no
wards and forwards from rib above to rib below. anterior cutaneous branch.
• Internal intercostal: this muscle fills the intercostal space from the • The 2nd intercostal nerve is joined to the medial cutaneous nerve of
sternum anteriorly to the angles of the ribs posteriorly where it becomes the arm by the intercostobrachial nerve branch. The 2nd intercostal
the posterior intercostal membrane which reaches as far back as the nerve consequently supplies the skin of the armpit and medial side of
vertebral bodies. The fibres run downwards and backwards. the arm.
• Innermost intercostals: this group comprises the subcostal muscles
posteriorly, the intercostales intimi laterally and the transversus thor- The diaphragm (Fig. 2.3)
acis anteriorly. The fibres of these muscles span more than one inter- The diaphragm separates the thoracic and abdominal cavities. It is com-
costal space. posed of a peripheral muscular portion which inserts into a central
The neurovascular space is the plane in which the neurovascular aponeurosisathe central tendon.
bundle (intercostal vein, artery and nerve) courses. It lies between the The muscular part has three component origins:
internal intercostal and innermost intercostal muscle layers. •A vertebral part: this comprises the crura and arcuate ligaments.
The intercostal structures course under cover of the subcostal The right crus arises from the front of the L1–3 vertebral bodies and
groove. Pleural aspiration should be performed close to the upper bor- intervening discs. Some fibres from the right crus pass around the lower
der of a rib to minimize the risk of injury. oesophagus.
The left crus originates from L1 and L2 only.
Vascular supply and venous drainage of the chest wall The medial arcuate ligament is made up of thickened fascia which
The intercostal spaces receive their arterial supply from the anterior overlies psoas major and is attached medially to the body of L1 and lat-
and posterior intercostal arteries. erally to the transverse process of L1. The lateral arcuate ligament is
• The anterior intercostal arteries are branches of the internal thoracic made up of fascia which overlies quadratus lumborum from the trans-
artery and its terminal branch the musculophrenic artery. The lowest verse process of L1 medially to the 12th rib laterally.
two spaces have no anterior intercostal supply (Fig. 2.2). The median arcuate ligament is a fibrous arch which connects left
• The first 2–3 posterior intercostal arteries arise from the superior and right crura.
intercostal branch of the costocervical trunk, a branch of the 2nd part of •A costal part: attached to the inner aspects of the lower six ribs.
the subclavian artery (see Fig. 60.1). The lower nine posterior inter- •A sternal part: consists of two small slips arising from the deep sur-
costal arteries are branches of the thoracic aorta. The posterior inter- face of the xiphoid process.
costal arteries are much longer than the anterior intercostal arteries
(Fig. 2.2). Openings in the diaphragm
The anterior intercostal veins drain anteriorly into the internal thor- Structures traverse the diaphragm at different levels to pass from
acic and musculophrenic veins. The posterior intercostal veins drain thoracic to abdominal cavities and vice versa. These levels are as
into the azygos and hemiazygos systems (see Fig. 4.2). follows:
• T8, the opening for the inferior vena cava: transmits the inferior vena
Lymphatic drainage of the chest wall cava and right phrenic nerve.
Lymph drainage from the: • T10, the oesophageal opening: transmits the oesophagus, vagi and
• Anterior chest wall: is to the anterior axillary nodes. branches of the left gastric artery and vein.
• Posterior chest wall: is to the posterior axillary nodes. • T12, the aortic opening: transmits the aorta, thoracic duct and azygos
• Anterior intercostal spaces: is to the internal thoracic nodes. vein.
• Posterior intercostal spaces: is to the para-aortic nodes. The left phrenic nerve passes into the diaphragm as a solitary
structure.
Nerve supply of the chest wall (Fig. 2.2)
The intercostal nerves are the anterior primary rami of the thoracic seg- Nerve supply of the diaphragm
mental nerves. Only the upper six intercostal nerves run in their inter- • Motor supply: the entire motor supply arises from the phrenic nerves
costal spaces, the remainder gaining access to the anterior abdominal (C3,4,5). Diaphragmatic contraction is the mainstay of inspiration.
wall. • Sensory supply: the periphery of the diaphragm receives sensory
Branches of the intercostal nerves include: fibres from the lower intercostal nerves. The sensory supply from the
• Cutaneous anterior and lateral branches. central part is carried by the phrenic nerves.

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