Anatomy of the Axilla: Structure and Boundaries (Upper Limb Anatomy I)

Anatomy of the Upper Limb

Introduction

The upper limb, or miembro superior, is a complex anatomical region essential for a wide range of movements and functions. This section focuses on the anatomy of the axilla (armpit), its boundaries, and its clinical significance.

Axilla (Armpit)

Overview

The axilla is a pyramidal space located between the upper limb and the thorax. It serves as a passageway for neurovascular structures traveling from the neck to the arm.

• Function: Conduit for nerves, blood vessels, and lymphatics to the upper limb.

• Shape: Pyramidal, with an apex (vértice), base, and four walls (anterior, posterior, medial, lateral).

Boundaries of the Axilla

The axilla is defined by its walls and apex, each formed by specific anatomical structures.

• Apex (Vértice): Also called the canal cervico-axilar, this is the superior opening of the axilla. It is bounded by:

  • Anteriorly: Clavicle

  • Posteriorly: Superior border of the scapula

  • Medially: Lateral border of the first rib (1ra costilla)

• Base: Formed by skin, subcutaneous tissue, and axillary fascia (not shown in these slides, but important for context).

• Anterior Wall: Formed mainly by the pectoralis major and minor muscles.

• Posterior Wall: Formed by the subscapularis, teres major, and latissimus dorsi muscles.

• Medial Wall: Formed by the thoracic wall (ribs 1-4 and intercostal muscles) and the serratus anterior muscle.

• Lateral Wall: Formed by the intertubercular sulcus of the humerus.

Key Terms and Definitions

• Canal cervico-axilar: The passageway at the apex of the axilla through which major neurovascular structures pass from the neck to the axilla.

• Scapula: The shoulder blade, a flat bone forming the posterior part of the shoulder girdle.

• Clavicle: The collarbone, forming the anterior border of the axilla's apex.

• First rib: The uppermost rib, forming the medial border of the axilla's apex.

Clinical Relevance

• Axillary contents: The axilla contains the axillary artery and vein, the brachial plexus, lymph nodes, and fat.

• Injury risk: Due to its contents, trauma or surgical procedures in the axilla can affect major vessels and nerves.

• Lymphatic drainage: Axillary lymph nodes are important in the spread of breast cancer.

Summary Table: Boundaries of the Axilla

Boundary	Main Structures
Apex (Vértice)	Clavicle (anterior), superior border of scapula (posterior), lateral border of 1st rib (medial)
Base	Skin, subcutaneous tissue, axillary fascia
Anterior Wall	Pectoralis major and minor muscles
Posterior Wall	Subscapularis, teres major, latissimus dorsi muscles
Medial Wall	Thoracic wall (ribs 1-4, intercostal muscles), serratus anterior
Lateral Wall	Intertubercular sulcus of humerus

Example: Passage of Neurovascular Structures

• The axillary artery and brachial plexus pass through the canal cervico-axilar at the apex of the axilla, supplying the upper limb.

Additional info: The axilla is clinically significant for procedures such as lymph node biopsy, nerve blocks, and management of traumatic injuries to the upper limb.