The subscapularis muscle (Latin for lower shoulder blade muscle) is understood as meaning a larger skeletal muscle of the shoulder. The inside of the scapula is completely covered by the subscapularis muscle. Its primary task is the internal rotation of the humeri (Latin for humerus).

What is the subscapularis muscle?

As an important component of the ventral group of the shoulder muscles, the subscapularis muscle is a central muscle in the rotator cuff. It starts on the inside of the scapula (shoulder blade).

Together with the other muscles of the rotator cuff, the infraspinatus muscle (Latin for lower bones), the supraspinatus muscle (Latin for the supraorbital muscle) and the teres minor muscle (Latin for small round muscle), it contributes to the head of the humeri in the socket and to stabilize.

Anatomy & Construction

The subscapularis muscle originates from the subscapular fossa, a bone depression on the ventral side of the scapula. It starts at the tubercle minus (small cusps) of the humerus as well as at the bony structure, which lies directly under it (Crista tuberculis minoris). Hereby, some of the tendon fibers of the muscle may extend into the shoulder joint capsule.

Of the muscles of the rotator cuff, the subscapularis muscle is the largest. Starting from there, it runs in the direction of the caput humeri (Latin for head of the humerus). The upper part of the muscle (as well as that of the supraspinatus muscle) runs between the shoulder-roof and the humeral caput. The nerve supply of the muscle is given by the subscapular nerve (Latin for sub-blade nerve). This is one of the branches of the brachial plexus (Latin for braid).

Function & Tasks

The primary task of the subscapularis muscle is to ensure internal rotation of the upper arm in the shoulder. Another main function is the adduction of the upper arm to the body, so the pre-accession. Likewise, the muscle can cause the abduction of the upper arm, ie its removal from the body.

By the adhesion of some muscle fibers of the subscapularis muscle with the capsule of the shoulder joint, the joint capsule is stretched and thereby stabilized. This muscle is an extraordinarily strong shoulder muscle. It has a high physiological cross-section, which results from its pronounced plumage. For the internal rotation of the upper arm, the subscapularis muscle is therefore the most important actor. The adduction is supported by the upper area, while the lower area of ​​the muscle ensures abduction. The stabilization of the humerus in the glenoid fossa (Latin for flat socket) prevents the bone from jumping out of the socket.

Similarly, pinching of the capsule of the shoulder joint is avoided in this way. The tendon of the muscle is very wide and therefore plays an important role in protecting against anterior shoulder luxation. Examples of the function of the muscle in everyday life are numerous, wherever internal rotation is required. A typical task for this muscle is, for example, steering while driving, with arms crossed in front of the body. Even when the safety belt is applied, internal rotation of the shoulder is effected.

Diseases

Often, the subscapularis muscle is included as part of the rotator cuff in the event of rupture of this cuff. Injury to the muscle can therefore cause the same symptoms of common rotator cuff rupture.

In addition to mostly severe pain, a violation of this muscle also shows a significantly impaired range of motion in the internal rotation of the upper arm. However, it is also possible that there is a simultaneous dislocation, that is, the shoulder is colloquially dislocated. Especially in certain accident events is a counter-collision in an abducted, so moved away from the body arm, typical. Such impacts on externally rotated arms are common in sports such as handball or volleyball. The pain is associated with the injury. The person concerned typically moves the arm away from his body in a pain-avoidance manner and supports it laterally.

The mobility of the shoulder is very limited, while the regular shoulder contour is missing. X-ray examinations, magnetic resonance imaging and magnetic resonance imaging are available for the diagnosis. In radiographs, the head of the upper arm is usually no longer visible in the socket. The two methods of tomography reveal possible cracks in the muscle. A limitation of the function of the subscapularis muscle can also be caused by a paralysis of the subscapular nerve, ie the nerve supplying the muscle. In this case too, the limitation of internal rotation is a central symptom.

In this case, especially the palm can only be moved with the help of other muscles to the back. Due to its important stabilizing function with respect to the humeral head, damage to the subscapularis muscle also affects the stability of the humeral head. Damage to the subscapularis leads to significant destabilization of the upper head. For example, the upper arm may slide forward until it rubs on the shoulder roof or on the processus Coracoideus (Latin for raven beak extension).

This phenomenon is known as shoulder impingement. This is not to be confused with the more frequently occurring outlet impingement, which is caused by a bony narrowing. Partial lesions on this muscle are problematic. The loss of function often remains unnoticed due to the large amount of tendons and the direct contact of the muscle to the upper arm below the tendon.

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