Anatomy, Thorax, Triangle of Auscultation

Lattisimus Dorsi

The latissimus dorsi is a large muscle forming the inferior border of the triangle of auscultation. It originates from the spinous processes of thoracic vertebrae seven though lumbar vertebrae five, the thoracolumbar fascia, the inferior angle of the scapula, the lower ribs, and iliac crest of the sacrum. It inserts onto the floor of the bicipital/intertubercular groove of the humerus. It acts to adduct, medially rotate, and extend the arm at the glenohumeral joint. It is innervated by the thoracodorsal nerve which originates from nerve roots C6 to C8.

Trapezius

 The inferior border of the trapezius muscle forms the superior border of the triangle of auscultation.  The trapezius muscle originates from the spinous process of cervical vertebrae seven through thoracic vertebrae 12.  It also originates from the protuberance of the occipital bone, ligamentum nuchae, and medial superior nuchal line. It inserts onto the lateral clavicle, the spine of scapula, and the acromion. There are three divisions of the trapezius muscle: the upper fibers, middle fibers, and lower fibers (the inferior border of the trapezius). The upper fibers act to elevate and superiorly rotate the scapula and extend the neck. The middle fibers function to adduct the scapula. The lower fibers serve to stabilize the scapula even further and assist the upper fibers in rotation of the scapula. Motor function of the trapezius derives from the accessory nerve, and proprioception follows the ventral rami of C3 and C4.

Teres Major

The teres major muscle forms the medial border of the triangle of auscultation along with the infraspinatus muscle. The teres major muscle originates from the inferior angle and lateral border of the scapula and inserts onto the intertubercular groove of the humerus. It acts to adduct, medially rotate, and extend the arm at the glenohumeral joint. It is innervated by the lower scapular nerve which originates from nerve roots C5 to C7.

Infraspinatus

The infraspinatus muscle along with the teres major muscle forms the medial border of the triangle of auscultation. The infraspinatus muscle originates from the infraspinous fossa of the scapula and inserts onto the greater tubercle of the humerus. It acts to laterally rotate the glenohumeral joint and helps stabilize the shoulder.  It is innervated by the suprascapular nerve which consists of nerve roots C5 through C6.

A thoracotomy is a procedure in which the thorax is opened surgically to gain access to the internal structures such as the lungs, pulmonary vasculature, heart, or aorta. This procedure is sometimes necessary to emergently evacuate a pericardial tamponade, control thoracic hemorrhage, internal cardiac massage or cross-clamp the descending thoracic aorta.  Access through the triangle of auscultation provides the patient with less perioperative morbidity as it spares incision through the latissimus dorsi.[9] Additionally, a pleurectomy is another procedure performed through thoracotomy access through the triangle of auscultation; this is useful in patients who have recurrent spontaneous pneumothoraces, as artificial obliteration of the pleural space and closure through a formal thoracotomy lead to excessive pain and discomfort.[10][11]

As stated above, the triangle of auscultation is an important anatomical landmark which allows for prime pulmonary auscultation. Auscultation of breath sounds is part of performing a routine lung examination. If a clinician does not hear equal air entry bilaterally, then it is time to consider conditions leading to airway obstruction such as inhaled foreign objects or a collapsed lung. If auscultation reveals wheezes, then the patient could have an obstructive condition such as chronic obstructive pulmonary disease (COPD) or asthma. If rhonchi are heard then the patient could be suffering from COPD, bronchiectasis, pneumonia, bronchitis, or cystic fibrosis. If the examiner hears rales, then fluid is trapped inside the alveoli and could be secondary to heart failure or pulmonary infection. An examiner can encounter all these findings during the pulmonary examination. The triangle of auscultation allows the clinician to listen better to the patient's lungs and guide them to the proper diagnosis.