SUBSCAPULARIS MUSCLE: CHARACTERISTICS, FUNCTIONS, SYNDROMES - ANATOMY AND PHYSIOLOGY - 2025

The subscapularis muscle is part of the rotator cuff. Therefore, it provides stability to the shoulder joint (glenohumeral), together with the supraspinatus, infraspinatus and teres minor muscles.

While the supraspinatus, infraspinatus, and teres minor muscles hold the glenohumeral joint superiorly and posteriorly, the subscapularis does so anteriorly.

Graphic representation of the subscapularis muscle. Source: Anatomography Edited image.

It should be noted that the stabilization of the shoulder on the anterior surface is not only a function of the subscapularis muscle, but also other structures such as the coracobrachial ligament, the anterior capsule itself and the ligaments of the glenohumeral joint, both superior, middle and inferior.

The participation of the subscapularis muscle in stabilizing the shoulder is limited to generating an eccentric tension, which regulates the anterior translational movement (slide). This function is possible thanks to the strategic origin and insertion points.

Other functions of the subscapularis muscle, apart from stabilizing the glenohumeral joint, is to assist in internal rotation of the shoulder. Also, depending on the position of the joint, it participates in the movement of abduction, flexion, extension and depression.

The subscapularis muscle originates in the anterior part of the shoulder blade or scapula, specifically in the fossa that bears the same name «subscapularis» and extends to the head of the humerus, inserting in greater proportion in the lesser tubercle, while a small portion does in the greater tuber.

The subscapularis muscle is the strongest of the 4 mentioned, and for this reason subscapularis tendinitis is difficult to diagnose, giving positive signs only when it is seriously injured.

characteristics

The muscle has a triangular shape, thick edges and a broad body.

Origin

The subscapularis muscle is located in the anterior part of the scapula, originating in the subscapular fossa, specifically in the costal area. The body or belly of the muscle covers the subscapular fossa. The muscle passes over the muscles of the back.

Insertion

The muscle attaches to the anterior portion of the humeral head, the area of ​​which is called the lesser tubercle or troquin.

Innervation

The subscapularis muscle is innervated by two nerves and as a result it is divided into two sections, upper-subscapularis and lower-subscapularis fibers, that is, upper and lower fibers of the subscapularis.

The first portion is innervated by the superior subscapular nerve (C5-C6) and the second by the inferior subscapular nerve (C5-C6). Both nerves come from the brachial plexus.

Irrigation

This muscle has a blood supply in charge of the transverse cervical artery and the subscapular artery mainly. However, a work published by Naidoo et al. showed that there are anatomical variations between one individual and another. To do this, they studied 100 corpses and observed the following:

In 96% of the cases, the subscapular muscle was supplied by the subscapular artery, in 39% by the thoracodorsal artery (branch of the internal subscapular artery), 36% by the suprascapular artery, in 14% by the lateral thoracic artery and in 9 % by the circumflex scapular artery (branch of the subscapular artery).

Features

It is a coaptator of the glenohumeral joint, that is, it contributes, together with other muscles, to keeping the head of the humerus stable in the glenoid cavity despite movements. The support function is fulfilled from the anterior face of the glenohumeral joint.

On the other hand, one of its main functions is to collaborate with the internal rotation movement of the shoulder, a function that it exercises together with other nearby muscles, such as: sternal fibers of the pectoralis major, teres major and latissimus dorsi.

However, internal rotation of the shoulder is not the only function it exercises, because depending on the position adopted by the humeral head in relation to the scapula, the subscapularis muscle can collaborate as: abductor, extensor, flexor and depressor.

It is even believed that it can help in external rotation movement in some positions, due to the joint insertion it has with the supraspinatus and infraspinatus muscles.

Some authors believe that the subscapularis muscle in the 90 ° abduction position at the level of the shoulder blade exerts a force equivalent to that of the infraspinatus and 2.5 times greater than that of the supraspinatus.

On the other hand, the function of the subscapularis muscle can be divided according to the area, that is, the upper part of the muscle fulfills one function and the lower part another.

In this sense, Ackland et al cited in Collard et al., Assure that the upper part of the subscapularis muscle is the one that most favors the internal rotation movement; obtaining a maximum point at 30 ° of flexion and abduction in the joint.

Whereas, the lower part is specifically responsible for stabilizing the posterior joint, counteracting the anterior translation.

Syndromes

One of the most common disorders that occur in the muscles that make up the rotator cuff is injury to the subscapularis muscle. The injury can be caused by contraction of the muscle (shortening) or overstretching (lengthening).

If the muscle is tense, trigger points can appear, which cause pain, which is easily correctable with rest and massage.

However, this may be the beginning of other, more complicated situations, which can generate chronic pain.

The location of the muscle gives it a peculiar situation, since of the four muscles the subscapularis is the only one that is positioned in the anterior part of the scapula. Therefore, its function as a co-receptor of the anterior aspect of the glenohumeral joint cannot be supplied by the rest of the muscles.

In any case, other nearby muscles such as the pectoralis major, the round and the latissimus dorsi can dominate the internal rotation movement, but these are not co-receptors of the glenohumeral joint.

In this sense, if the muscle becomes weak or lengthens, the reinforcement of the glenohumeral joint in its anterior part will be threatened, remaining only at the expense of the joint capsule and the coracobrachial and glenohumeral ligaments, which are less strong.

This situation causes an exaggerated anterosuperior gliding, a symptom that precedes the subacromial syndrome.

- Subscapularis tendonitis

In external rotation, the normal thing that should happen is that the external rotator muscles contract, while the subscapularis is stretched. The found forces generated on both sides of the joint are what provide stability to the humeral head in the glenoid socket.

However, the subscapularis muscle can become weak or elongated as a result of stiffness or shortening in the external rotator muscles.

This causes a limitation in internal rotation, since the effort made by the subscapularis muscle during external rotation under this circumstance causes it to stretch too much and over time to weaken.

Other factors that can injure the muscle are found in: the adoption of bad postures, the excessive use of the shoulder joint, sudden movements without warming up, static positions for a long time or previous degenerative diseases such as arthritis, among others. Several causes can coexist at the same time.

Signs and symptoms

Most tears occur at the level of the tendon-bone junction (tenoperiosteal junction). This involvement causes pain in the back of the arm and occasionally the pain can radiate to the wrist.

Likewise, a tear of the subscapularis muscle at the level of the muscle belly produces pain at the level of the scapula, but this is not frequent.

The tear is usually healed naturally with scar tissue, but it is easily ruptured with moderate effort. If this situation is repetitive, the muscle weakens and becomes painful.

Depending on the cause, the symptoms may appear gradually or suddenly. In cases of slow progression, the patient mainly complains of pain when raising the arm above the shoulder, whatever the activity is performed.

In acute cases the problem occurs after a sudden movement, producing strong discomfort with simple maneuvers, such as: opening a door or unscrewing a cover.

If the problem is not corrected, it can cause a frozen shoulder (without movement) or osteoarthritis problems.

Subscapularis injury can also present in conjunction with a dislocation of the shoulder joint. In this case, the pain can last for months.

- Examination of the subscapularis muscle

Rotation resisted

The patient is asked to perform a resisted rotational movement and, if there is pain, the subscapularis muscle is affected.

Gerber test

To do this, the arm is positioned behind the patient's back. The elbow should be flexed 90 °. Then it is tried to resist the internal rotation movement and it is observed if there is pain.

- Treatment

Although the muscle is very difficult to palpate, some massages can be done that can relieve pain.

There are two techniques of self-massage, the first called pressure-movement, which consists of touching the muscle and exploring the areas of pain, while performing the internal and external rotation of the shoulder joint repeatedly.

While the second is called the thumb technique. The thumb is placed in an area immediate to the point of pain to begin to massage it repeatedly.

Stretching exercises are also very helpful.

Related disorders

Subacromial impingement syndrome

It is also known as rotator cuff tendonitis or impingement. It is a very common condition in young patients.

It develops in three stages:

1) Edema and inflammation of the affected muscle.

2) Compression of the rotator cuff due to fibrosis and thickening of the subacromyodeltoid serous bag.

3) Partial or total rupture of the muscles that make up the rotator cuff, the subscapularis muscle may be involved.

References

1. "Subscapularis muscle" Wikipedia, The Free Encyclopedia. 15 Aug 2018, 23:21 UTC. 9 Sep 2019, 19:31 org /
2. Collard P, Pradere M, Rusquet A. The role of the subscapularis muscle in anterior glenohumeral stability. Special degree work to obtain the title of physiotherapy. 2017-2018. Available at: eugdspace.eug.es
3. Naidoo N, Lazarus L, De Gama B. Z, Ajayi N. O, Satyapal KS Arterial Supply to the Rotator Cuff Muscles. J. Morphol. 2014; 32 (1): 136-140. Available at: scielo.conicyt.
4. Saldaña E. (2015). Manual of human anatomy. Available at: oncouasd.files.
5. Pereira V, Escalante I, Reyes I, Restrepo C. Association of subacromial impingement syndrome and partial intra-articular shoulder injuries. VITAE Digital Biomedical Academy. 2006; 28 (1): 1-16. Available at: vitae.ucv.ve