Pectoralis Major Muscle: Origin, Insertion, Functions, Syndromes

The  pectoralis major muscle belongs to the group of paired superficial muscles of the anterosuperior region of the thorax, in fact, it is the most superficial of all the muscles in the area. It is located below the mammary glands, above the pectoralis minor muscle. In Latin it is written musculus pectoralis major.

It is a wide, flat and bulky muscle. It is triangular in shape, similar to that of a fan. It has four sides, three corresponding to the origin of its fibers. These are supported by neighboring bone structures and ligaments and the fourth side corresponds to the site where the fibers end (single point of insertion).

The deltopectoral groove separates the pectoralis major muscle from the deltoid muscle. Another fact that stands out is that the pectoralis major muscle forms the anterior axillary fold, this fold being easily palpable.

It is a highly resistant muscle, very tonic and is very frequently exercised in gyms, since its development produces a very attractive aesthetic image, in addition to obtaining health benefits.

Exercises that strengthen the pectoralis major include incline bench press, incline dumbbell bench openings, low pulley crossovers, raised leg push-ups.

Origin

Due to its large size, the muscle covers three areas of origin. Its upper limit emerges from the clavicular head, specifically its medial third (anterior face), whose fibers project downward.

The medial lateral limit of the muscle encompasses the sternum (anterior lateral), from the manubrium to the body of the sternum, touching the first six sternocostal joints (cartilage). Its fibers travel horizontally.

In turn, the lower part has points of origin in the sternocostal head, with a point of origin from the aponeurosis corresponding to the neighboring muscle, called the external oblique, as well as towards the anterior lamina in the sheath of the rectus abdominis muscles. . Its fibers are oriented upward.

Insertion

The muscle fibers converge at a single point, located on the lateral lateral lip of the humerus (intertubercular sulcus), also known as the humerus bicipital groove. The insertion is made in two blades (anterior and posterior).

Innervation

This muscle is innervated by branches of the brachial plexus, specifically by the medial pectoral nerve C8 and T1 and the lateral pectoral nerve (C5, C6 and C7).

Irrigation

The thoracoacromial artery emits branches to the muscle in question, these are called pectoral branches. On the other hand, the pectoralis major muscle is also nourished by the intercostal arteries, specifically in the lower part of the muscle.

Features

It has several functions, including allowing the arm to adduct, that is, to bring the arm closer to the trunk of the body. It also participates in medial internal rotation of the shoulder to a lesser extent, as well as in flexion and extension of the shoulder.

The pectoralis major muscle has fibers in different directions (horizontal, descending, ascending), each fulfilling a different function.

In this sense, the descending fibers exert the flexor function, the horizontal fibers carry out the adduction and medial rotation of the shoulder and finally the ascending fibers fulfill an extensor function.

The muscle can also collaborate with other movements such as: shoulder anteversion (move the arm forward) or shoulder protraction (shoulder forward).

On the other hand, during respiration (inspiratory movement) the pectoral muscle ascends the ribs outwards. This action allows the thoracic area to be expanded, which is why athletes, especially marathoners, need to have well-developed pectorals, as it will allow them to breathe better when they are in competition.

That is why the pectoralis major is considered an accessory muscle of respiration.

Syndromes

Trigger points

The pectoralis major muscle can be stressed and present trigger points or pain. Trigger points can cause pain in the chest, shoulder, or can even radiate to the elbow, forearm, and wrist.

The pain caused by trigger points could be confused with other pathologies, such as: angina pectoris, radiculopathies, muscle fissure, thoracic outlet syndrome.

A self-massage of the muscle is possible to improve symptoms. (See next video).

Poland syndrome

This syndrome was first discovered and reported in the 19th century by Dr. Alfred Poland. It is a strange syndrome of unknown cause quite complex. It usually has multiple malformations, among them is atrophy of the pectoralis major muscle and even in some cases the muscle does not exist.

This can coincide with hypoplasias of other muscles and tissues close to it, especially the pectoralis minor, muscles of the scapular region and the subcutaneous tissue.

In addition, the patient may concurrently present with other important abnormalities, such as: ipsilateral absence of ribs, brachydactyly (incomplete development of a limb), ectromelia (defective forearm and wrist), axillary crease, syndactyly (sticking fingers), distortions of the hemithorax or amastia (absence of a breast), among others.

Isolated agenesis of the pectoral muscle

It is a moderately frequent muscular anomaly, occurring approximately 1 case in a range of 4,000 to 20,000 births.

This abnormality is underdiagnosed, as it can sometimes be overlooked. It is characterized by the total or partial unilateral absence of one of the major pectoral muscles, generally the right one and with a higher prevalence in males. Bilateral absence of the muscle is rarer. It is considered a slight variation of the Poland syndrome explained above.

The most notable manifestation is chest and breast asymmetry on the affected side.

According to a case described by Goñi et al. In 2006, the 9-year-old male pediatric patient did not present any other abnormality or dysfunction, other than the lack of the right pectoral muscle.

Pectoralis tertius or third muscle

It is a supernumerary anatomical variant of the pectoralis major muscle, where the presence of a third muscle has been found. The insertion of the third muscle has been seen to occur in a different place than usual.

The anatomical sites of insertion found so far for the third muscle are: the coracoid process, the medial epicondyle of the humerus, in the capsule of the shoulder joint and on the greater or lesser tubercle of the humerus.

Likewise, other authors have reported insertions in the fascia of the arm, the short-head tendon of the biceps brachii muscle or the tendon of the coracobrachialis muscle, among others.

On the other hand, other malformations in the pectoralis major have been described in the literature, among which are: absence of the abdominal or lower part of the muscle, the union with its counterpart in the midline and the non-existence of the lower sternocostal area .

Strengthening the pectorals

The exercises most recommended by specialists to strengthen this muscle are the following: incline bench press, incline dumbbell bench openings, low pulley crosses, raised leg push-ups. (see next video).

Surgical techniques

The pectoralis major muscle and the external oblique muscle are used for breast reconstruction after a mastectomy. Surgeons with both muscles create a pocket where the prosthesis will rest. Then they cover it with a skin-adipose flap.

The pectoralis major myocutaneous flap technique is also used for reconstruction of cervical defects.

References

  1. Goñi-Orayen C, Pérez-Martínez A, Cabria-Fernández A. Isolated agenesis of the pectoralis major muscle: Underdiagnosed pathology? Acta Pediatr Esp . 2006; 64: 189-190.
  2. «Pectoralis major muscle»  Wikipedia, The Free Encyclopedia . 16 Sep 2019, 21:01 UTC. 26 Sep 2019, 02:13 wikipedia.org
  3. Urquieta M, Ávila G, Yupanqui M. Supernumerary anatomical variant of the Pectoralis Major Muscle (third pectoral). Rev Med La Paz , 2016; 22 (1): 96-102. Available at: Scielo.org
  4. Saldaña E. (2015). Manual of human anatomy. Available at: oncouasd.files.wordpress
  5. Dávalos-Dávalos P, Ramírez-Rivera J, Dávalos-Dávalos P. Pectoralis major and external oblique flaps for coverage of expanders and / or prostheses in postmastectomy reconstruction. plast. iberolatinoam . 2015; 41 (1): 33-39. Available in: scielo.
  6. García-Avellana R, Márquez-Cañada J, Tejerina-Botella C, Godoy-Herrera F, Noval-Font C, García Avellana R. et al. Our pectoralis major myocutaneous flap technique for reconstruction of cervical defects. plast. iberolatinoam . 2017; 43 (3): 285-293. Available at: scielo.isciii.es.

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