Anterolateral thoracic wall

The anterolateral thoracic wall refers to the upper part of the anterior trunk. It comprises of the anterolateral chest wall and its associated structures.

The anterolateral thoracic wall acquires its primary support from the underlying bony framework that is formed by the sternum anteriorly, with its three sub-parts, i.e. the manubrium, body and xiphoid process. In addition, twelve pairs of ribs, also contribute to the anterolateral thoracic wall. Of these, the first seven being true ribs, while remaining five being false ribs. The true ribs are connected directly to the sternum via their costal cartilages. Whereas, the false ribs are either indirectly connected to sternum via the costal cartilage of the seventh rib or they are free floating ribs (eleventh and twelfth ribs). The floating ribs do not attach to the sternum and hence, cannot be seen anteriorly.

Small intercostal muscles can be found situated within the intercostal spaces (between successive ribs). From outside to inside, these include the external intercostal, internal intercostal and innermost intercostal muscles; all innervated by intercostal nerves. They support the intercostal spaces and aid in respiration.

A pectoral region can be found anterior (or superficial) to the anterolateral thoracic wall. Its constituent parts hold the upper limb to the upper trunk. Two important muscles situated in the pectoral region include the pectoralis major and minor muscles, both originating from the bony anterior chest wall. The former inserts into the upper end of humerus, while the latter inserts into the coracoid process of scapula. An additional muscle, called the serratus anterior (a.k.a. the boxer muscle) originates as eight individual slips from the sides of the upper eight ribs. It wraps around the lateral thoracic wall and extends posteriorly to insert into the medial border of scapula. It functions to stabilize the scapula on the posterior rib cage and helps in protracting the scapula when throwing a forward punch. Last but not the least, a muscle called the subclavius can also be found underneath the clavicle, attaching it to the first rib. It helps to pull the clavicle and stabilizes it on the sternoclavicular joint.

The muscles of the pectoral region are covered over by a layer of deep fascia, which in turn is wrapped up by the superficial fascia and the skin. Mammary glands or the breast tissue can be found within the superficial fascia in front of the anterolateral thoracic wall.

The nerves and vessels which supply the thoracic wall reside inside the subcostal groove underneath each rib. The neurovascular bundle comprises of intercostal veins, arteries and nerves:

• Intercostal nerves–are continuations of anterior rami of spinal nerves,

• Anterior intercostal arteries–arise from internal thoracic and musculophrenic arteries,

• Posterior intercostal arteries–arise mainly from the thoracic aorta,

• Anterior intercostal veins–drain into internal thoracic veins,

• Posterior intercostal veins–drain into azygous and hemiazygos system of veins.