Axillary lines

The left side of the thorax with lines labeled

The axillary lines refer to imaginary vertical lines on the human body that run through the axilla (the armpit). They play a crucial role in clinical examinations and descriptions, particularly in thoracic procedures, as they serve as reference points. These lines are categorically divided into three distinct lines: the anterior axillary line, midaxillary line, and the posterior axillary line.

Description

Each of the axillary lines offers specific information and is located in a particular area of the axilla:

Anterior Axillary Line

This line runs vertically down from the anterior axillary fold, which is where the pectoralis major muscle of the chest connects with the upper arm. Clinically, this line is of significance in thoracentesis, a procedure where fluid is removed from the pleural space.

Midaxillary Line

The midaxillary line is positioned halfway between the anterior and posterior axillary lines, extending from the apex of the axilla and running down the middle of the lateral aspect of the chest and abdomen. This line serves as an important landmark in many surgical and diagnostic procedures, including the insertion of chest tubes.

Posterior Axillary Line

Originating from the posterior axillary fold, where the latissimus dorsi muscle of the back joins with the upper arm, the posterior axillary line runs vertically downward. This line is frequently used as a landmark in procedures targeting the posterior thoracic and abdominal regions.

Clinical Relevance

The axillary lines are pivotal for many clinical procedures. For example:

• During thoracentesis, the anterior axillary line often serves as the lateral boundary.
• The midaxillary line can be used as a guide for the safe placement of chest drains, ensuring they are inserted in the correct position to prevent injury to internal structures.
• In cardiology, the apex beat can be located in relation to the midaxillary line.

Moreover, these lines help in accurately describing the location of wounds, rashes, or other skin lesions in the lateral thoracic and abdominal areas.

See Also

• Anatomical terms of location
• Thoracentesis
• Chest tube

See also

• Anatomical terms of location

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