SERRATUS ANTERIOR: ORIGIN, FUNCTIONS, SYNDROMES, DISORDERS - ANATOMY AND PHYSIOLOGY - 2025

The serratus anterior or serratus major as it is also known, is a paired muscle located on both sides of the chest (right and left side) that specifically covers the lateral part of the first ribs (upper part of the thorax). Its name comes from the Latin musculus serratus anterior.

The serratus anterior muscle is born in the first 9 ribs, and through various fingerings, it is strategically inserted into the shoulder blade or scapula, the union is established according to the point of origin, some converge, that is, they join at the same point and others diverge (they are fixed separately).

Location of the serratus anterior muscles (right and left). Source: Bildbearbetning: sv: Användare: Chrizz. * compressed with pngcrush. Edited image.

The serratus anterior joins the shoulder blade with the ribs and this makes it a multifunctional muscle. Its main function is to achieve stabilization of the shoulder blade through its attachment to the thorax, so much so that when this muscle weakens and becomes paralyzed, it produces what is known as the scapula alata or winged.

On the other hand, the shoulder blade is able to ascend or descend thanks to this muscle, it also allows the arm to be raised above 90 °. Likewise, the upward movement of the ribs during inspiration is largely attributed to the serratus anterior.

Overloading this muscle can cause pain points, also called trigger points, to appear. The pain may radiate to the ribs, shoulder blade, and inner arms. Trigger points can be removed through massage.

characteristics

The serratus anterior or greater, is a thin and flat muscle, with a superficial location. Its surface is toothed (in the shape of a saw), hence its name "serrato". It has long and thin beams. To feel it, just place your fingers on one of the sides.

Below the serratus anterior is the thoracic cage and behind this it relates to the subscapularis muscle, and in front with the pectoralis major and minor. Between the serratus anterior and the aforementioned structures there is interposed a fat-cell membrane that covers the entire muscle and helps it to slide.

The serratus anterior and the trapezius are muscles that work synergistically, both in the rotation of the scapula and in the abduction of the arm. They also make the scapula stay attached to the thorax.

Origin

For didactic reasons, the serratus anterior muscles (right and left) can be divided into three zones (upper, middle and lower), thus facilitating the description of origin, insertion and functions.

Thus, the upper part comprises the area that covers the first and second rib (first point of origin). The middle part is represented by the area that covers the second and third rib (second point of origin) and the lower part refers to the area corresponding to the fourth and ninth rib (third point of origin).

In all cases the muscle arises in the anterolateral position of each mentioned rib.

Insertion

The muscle fibers from ribs I and II converge moderately to the superior medial edge or angle of the shoulder blade; those coming from ribs II to IV diverge to the medial edge of the shoulder blade; and the last ribs V to IX converge strongly on the edge or lower angle of the shoulder blade.

Innervation

The long thoracic nerve (nervus thoracicus longus) emanates from the anterior C5-C7 branches of the brachial plexus and is responsible for innervating the serratus anterior muscle, which is why some authors call it the serratus major nerve.

However, other sources also call it the Charles Bell nerve or Bell's external respiratory nerve.

The injury to this nerve causes weakness, paralysis and atrophy of the muscle, causing the pathology known as scapula alata.

The nerve passes behind the mid-axillary line and continues below the pectorals and then descends vertically to the fourth or fifth fingering of the serratus anterior, from where ramifications emerge into the muscle.

Irrigation

The serratus anterior muscle is supplied by a branch of the lateral thoracic artery and by a branch of the circumflex scapular artery.

Features

Continuing with the division of the muscle into the three areas already explained above, it can be said that the scapula can be raised thanks to the upper part of this muscle and can be lowered by the action of the middle and lower part.

Also, the lower part of the muscle allows the shoulder blade to separate its base outward and rotate, making it possible to lift the arm above 90 ° (external tilt), an action that it performs together with the trapezius.

On the other hand, as this muscle participates in the elevation of the ribs during the inspiration movement, it is said to be an accessory muscle of respiration.

The muscle in general serves as support to give stability to the shoulder blade, especially in activities in which pressure is exerted on the shoulder, examples: using crutches to walk, doing elbow flexion exercises (push-ups), practicing bench press, among others.

In this sense, the muscle makes resistance to prevent the shoulder from going out of its normal limits.

Syndromes or related disorders

Trigger points in the serratus anterior

Trigger points are muscle contractures that are concentrated in one or more specific sites and are felt as indurated areas. These points are painful on palpation and also when trying to move or stretch the muscle. The pain affects the ribs, part of the shoulder blade, and can radiate into the upper extremities.

Its contracture can even make it difficult to breathe, making the inspiration movement short. This is a defense mechanism that the patient adopts, because the simple breathing bothers him. Therefore, he is limited to activities that speed up breathing, such as running.

The serratus anterior muscle recharges when it is pushed for more than it is used to. For example lifting a very heavy object unusually and raising it above the head.

That is why, people who decide to start doing a sport or activity and who demand more effort from this muscle, should do it gradually. Example: jogging, elbow flexion or bench press, among others.

An excessive cough can also cause pain at the level of this muscle, since during coughing the muscle is overloaded by rapid and strong inspiration movements.

Trigger points can be removed with massage. These can be done gently with your fingers or with a ball. The painful points are located (usually between the fifth and sixth rib) and over them, gentle movements are made with the fingers or the ball is gently rotated.

Scapula alata or winged

It comes from the Latin scapula alata. This pathology is caused by injury to the long thoracic nerve. The injury causes the muscle to paralyze, causing it to atrophy. Therefore, it is characterized by deformity (medial unevenness) of the scapula or shoulder blade.

This injury directly affects the mobility of the shoulder. Flexibility will be drastically diminished, both in strength and reach.

The nerve can be affected due to surgeries performed along the path of the nerve, due to trauma or due to excessive weight loads.

To diagnose this condition, the patient is asked to stand shirtless in front of a wall. Then you should raise your arms forward and lean against the wall, trying to push it. If the scapula is observed to protrude backwards, it is considered a positive test.

The patient is also asked to fully raise both arms up, placing the thumbs back and then lowering them. If there is impediment, discomfort or pain when performing the exercise, there may be problems with the serratus anterior.

References

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