Infraclavicular region as the basis of the axillary fossa
The infraclavicular region (regio infraclavicularis) plays a key role in the formation of the axillary fossa. From the standpoint of topographical anatomy, this zone is traditionally viewed as an integral part of the shoulder girdle, although anatomically it belongs simultaneously to both the thorax and the upper limb. It is precisely to this region that the most important neurovascular bundle of the arm—the axillary bundle—closely adheres.
To navigate this zone accurately, it is necessary to know its external landmarks. These include the clavicle, sternum, contours of the pectoralis major muscle (m. pectoralis major), and the anterior border of the deltoid muscle (m. deltoideus).
The boundaries of the infraclavicular region form a distinct quadrilateral:
- Superior boundary: clavicle.
- Inferior boundary: a conventional horizontal line passing at the level of the third intercostal space.
- Medial boundary: lateral edge of the sternum.
- Lateral boundary: anterior border of the deltoid muscle.
It is also important to remember the projection of the pectoralis minor muscle (m. pectoralis minor). It projects onto the anterior thoracic wall as a small triangle, the apex of which points toward the coracoid process (processus coracoideus), while the base rests against the anterior ends of the 3rd, 4th, and 5th ribs.
Key topographical formations
Within the infraclavicular region, several structures critically important for the surgeon are distinguished.
- Infraclavicular fossa (fossa infraclavicularis). In surgical practice, it is also known as Mohrenheim's fossa. This depression is localized slightly inferior to the clavicle, strictly at the border between its lateral and middle thirds. The space of the fossa is bounded by two muscle masses: the clavicular part of the pectoralis major muscle on one side and the anterior border of the deltoid muscle on the other.
- Deltopectoral groove (sulcus deltopectoralis). It serves as a direct distal continuation of the infraclavicular fossa. The groove descends inferiorly along the anterior border of the deltoid muscle, heading all the way to the lateral bicipital groove of the arm.
- Coracoid process of the scapula (processus coracoideus). This is an important bony landmark that can be palpated deep within the deltopectoral groove. The point of palpation is located 1.5–2 centimeters below the level of the clavicle.
Cellular spaces and neurovascular bundle
The axillary fossa itself is filled with adipose tissue, which serves as a bed for the main neurovascular bundle of the upper limb. This bundle includes the axillary artery (a. axillaris), the corresponding axillary vein (v. axillaris), and the cords and branches of the brachial plexus (plexus brachialis).
The adipose tissue of the upper division of the axillary fossa is localized in the deep subpectoral space. The posterior boundary of this space is formed by the deep thoracic fascia (fascia thoracica). This fascia densely covers the serratus anterior muscle and the intercostal spaces.
The posterior wall of the axillary fossa itself is formed by the scapula. It also forms the posterior wall of the prescapular cellular space. This space represents a direct continuation of the axillary cellular space in the dorsal (posterior) direction. Anteriorly, the prescapular space is bounded by the serratus anterior muscle (m. serratus anterior), which is also covered by its own fascia.
Blood supply to adjacent regions and venous anastomoses
When studying the topography of the axillary fossa, one cannot ignore its vascular connections with the anterolateral abdominal wall. The venous system of these areas forms vital collateral pathways.
Superficial veins of the anterior abdominal wall and chest — thoracoepigastric veins (vv. thoracoepigastricae) — play the role of a connecting link. They connect the femoral vein system with the axillary vein drainage area, forming a powerful cavocaval anastomosis.
In addition, porto-caval and other caval-caval anastomoses are formed in the umbilical region. These involve the paraumbilical veins (vv. paraumbilicales) passing within the round ligament of the liver, as well as the superior and inferior epigastric veins (v. epigastrica superior and v. epigastrica inferior). The superior epigastric vein carries blood into the internal thoracic vein and further into the superior vena cava system, while the inferior epigastric vein drains into the external iliac vein (inferior vena cava system). In portal hypertension, the umbilical veins undergo compensatory dilation, which clinically manifests as the caput Medusae sign.
The arterial blood supply to these adjacent zones also features a complex network of anastomoses. For instance, the superior epigastric artery (a. epigastrica superior, the terminal branch of the internal thoracic artery) descends into the rectus abdominis sheath from above and anastomoses with the inferior epigastric artery (a. epigastrica inferior, a branch of the external iliac artery), which ascends from below. The inferior epigastric artery serves as a critical landmark in inguinal canal surgery: medial to it lies the medial inguinal fossa, and lateral to it lies the lateral inguinal fossa. The lateral parts of the abdominal wall receive blood from the lower posterior intercostal (aa. intercostales posteriores VII–XI), subcostal (a. subcostalis), and lumbar arteries (aa. lumbales).
To memorize the boundaries of the infraclavicular region, imagine a square: superiorly—the clavicle, inferiorly—the 3rd intercostal space, medially—the sternum, laterally—the deltoid muscle.
Class and exam questions
What forms the posterior wall of the axillary fossa?
The posterior wall is formed by the scapula. It also serves as the posterior boundary of the prescapular cellular space, which continues the axillary space in the dorsal direction.
Where is the coracoid process of the scapula palpated?
It can be palpated deep within the deltopectoral groove. The palpation point is located approximately 1.5–2 cm below the clavicle.
What contents are found in the deep subpectoral space?
It houses the adipose tissue of the upper division of the axillary fossa. The posterior boundary of this space is formed by the deep thoracic fascia.
How is the axillary vein connected to the abdominal veins?
The connection is established via the superficial thoracoepigastric veins. They form a caval-caval anastomosis, connecting the basins of the axillary and femoral veins.
What else to study on this topic
- Topographical anatomy of the triangular and quadrangular spaces.
- Pathways of pus spread from the axillary fossa.
- Blood supply to the anterolateral abdominal wall (superior and inferior sources).
- Porto-caval and caval-caval anastomoses of the umbilical region (caput Medusae sign).
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