Anatomy

Triangle of auscultation

Triangle of Auscultation: All the things we need to know

Triangle of auscultation is an important landmarks which resembles a small triangular interval. It is bounded medially by the lateral border of the trapezius muscle, laterally by the medial border of the scapula, and inferiorly by the upper border of the lattisimus dorsi. Auscultation triangle is mainly used to auscultate the apex of the lungs.  We can hear the respiratory sound clearly here because these places are not covered by big muscles.

The 5th and 7th rib, and 6th intercostal space (ICS), and the rhomboid major forms the floor of the triangle. The triangle of auscultation is the part of back where no big muscles covers it. Respiratory sounds of apex of lower lobe heard through a stethoscope are better heard over this triangle on each side. In early times when X-rays were not discovered an oesophageal tumour was noticed by hearing the sound of liquids that were swallowed and auscultating over this triangle to confirm it on the basis of the sound heard.

Boundaries: Triangle of auscultation

The boundaries are listed below:

  • Medially: By the Trapezius muscle’s lateral border
  • Laterally: By the scapula’s medial border
  • Inferiorly: By the lattssisimus dorsi’s upper border  
  • Floor: By the 5th and 7th rib, and 6th intercostals space, and the rhomboid major.

Muscles of Triangle of auscultation:

The mucles present in the triangle of auscultation is given below:

1. Lattisimus Dorsi

This muscle form the inferior border of the triangle of auscultation and it is a large muscle.

Origin: 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

Insertion: In humerus i.e Floor of the bicipital/intertubercular groove

Action: In adduction, medially rotate, and extend the arm at the glenohumeral joint.

Innervation: By the thoraco-dorsal nerve which originates from nerve roots C6 to C8.

2. Trapezius

It forms the superior border of the triangle of auscultation. 

Origin: 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.

Insertion: The lateral clavicle, the spine of scapula, and the acromion.

Action: To elevate and superiorly rotate the scapula and extend the neck, to adduct the scapula, to stabilize the scapula even further and assist the upper fibers in rotation of the scapula.

Innervation: Accessory nerve, and the ventral rami of C3 and C4.

3. Teres Major

It forms the medial border of the triangle of auscultation.

Origin: The inferior angle of scapula and lateral border of the scapula

Insertion: Onto the inter-tubercular groove of the humerus.

Action: Acts to adduct, medially rotate, and extend the arm at the gleno-humeral joint.

Innervation: By the lower scapular nerve which originates from nerve roots C5 to C7.

4. Infraspinatus

It forms the medial border of the triangle of auscultation.

Origin: From the scapula i.e the infraspinous fossa

Insertion: Onto the greater tubercle of the humerus.

Action: It acts to laterally rotate the joint called the gleno-humeral and aids in stabilizing the shoulder. 

Innervation: Innervated by the supra-scapular nerve which consists of nerve roots C5 through C6.

Do read: Ball and socket joint

Clinical significance:

For a pulmonary auscultation and thoracic procedures triangle of auscultation is very useful. Respiratory sounds are audible more clearly with a stethoscope and it is due to muscle’s nature i.e they are thin and the posterior thoracic wall being closer to the skin surface. The cardiac orifice of the stomach in the left side lies deep to the triangle.

In early times when X-rays were not discovered an oesophageal tumour was noticed by hearing the sound of liquids that were swallowed and auscultating over this triangle to confirm it. It is covered by scapula. If you want to expose the floor of the triangle then you need to fold your arm across your chest and rotate the scapula laterally and bend forward the trunk which resembles somewhat a fetal position.

It is also used as a surgical approach path. For the rhomboid intercostal nerve block it is used as it can help to relieve pain after rib fractures.

Takeaway:

Triangle of auscultation is an important landmarks. It is formed by muscles like the trapezius muscle, the scapula and the lattisimus dorsi. Triangle of auscultation is mainly used to auscultate the apex of the lungs.  We can hear the respiratory sound clearly here because these places are not covered by big muscles. It is also used as a surgical approach path. For the rhomboid intercostal nerve block it is used as it can help to relieve pain after rib fractures.

Rashmi Shrestha

Namastey!! I am Rashmi Shrestha. I am an ethusiast writer and reader. I am currently reading Bsc. Human biology in Kathmandu University. I love to read poetry and write some too.

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