SHOULDER GIRDLE: JOINTS, MUSCLES - ANATOMY AND PHYSIOLOGY - 2024

The shoulder girdle is a set of bones that connects the upper limb to the axial skeleton on the left and right sides of the body and serves as the attachment site for the muscles of the upper back, chest, and neck. It extends from the base of the neck to the lower part of the pectoralis major.

The shoulder girdle possesses the greatest range of movements of all the joints of the body, for this reason its understanding and health is important to avoid injuries that threaten the daily routine of the person.

Joints and their functions

The shoulder girdle is made up of three joints: glenohumeral, acromioclavicular, and sternocostoclavicular.

Glenohumeral joint

It is the main joint, it forms what people commonly think of as the shoulder joint. The glenohumeral connects the humerus (arm) with the thorax (chest). The tendon of the long head of the biceps and the glenohumeral ligaments are attached to it.

It allows a wide range of movements such as flexion, extension, abduction, adduction, rotation, and circumvallation. However, its mobility makes the joint relatively unstable.

The muscles on the lateral side of the shoulder allow for movement and stability of the joint. These muscles are tough on the upper and back sides of the arm, but not on the bottom. A strong external force in this area can cause what is known as a dislocation.

The glenohumeral joint is supported by its articulated fibrous capsule and the following ligaments: transverse humeral ligament, coracoacromial ligament, and glenohumeral ligament.

Acromioclavicular joint

The acromioclavicular joint helps to unite the arm with the body in the chest. It is located 2 or 3 cm from the point of the shoulder formed by the lateral part of the acromion.

Due to the poor bone stability in this joint, a series of ligaments and other soft tissues are responsible for stabilizing this joint.

Some of these structures are the acromioclavicular ligament, the loose fibrous joint capsule, the nearly horizontal trapezoidal ligament, the vertical conical ligament, and the coracoclavicular ligament.

The superior acromioclavicular ligament is the most important horizontal stabilizer. The coracoclavicular ligaments allow the clavicle to be stabilized vertically.

A significant amount of rotation occurs at the clavicle and about one-tenth of this occurs at the acromioclavicular joint.

Sternocostoclavicular joint

It is the only joint between the upper extremity and the axial skeleton, and is easily palpable because the sternal end of the clavicle is superior to the manubrium of the sternum.

It works like a "ball joint". The sternocostoclavicular joint is divided into two compartments by an articular disc.

The disc is firmly attached to the anterior and posterior sternoclavicular ligaments, thickenings of the fibrous layer of the joint capsule, as well as the interclavicular ligament.

The sternoclavicular joint is primarily responsible for the rotation and stability of the joint comes from the soft tissues.

The posterior sternoclavicular joint capsule is the most important structure to prevent forward and backward displacement of the medial clavicle.

Muscles and their functions

Angular muscle of the shoulder blade

It begins at the vertebral and superior edge of the scapula and its insertion at the transverse tips of the first 4 cervical vertebrae.

Its function is to stabilize the lateral movements of the body, as well as to raise the scapula.

Biceps brachii muscle

It is located next to the coracobrachialis muscle and consists of two heads; the long head and the short head.

Its function is to flex the elbow, assist in shoulder flexion and contribute to separation with the shoulder in external rotation. When the elbow is not fully extended, it performs a powerful supination of the forearm.

Coracobrachialis muscle

This muscle is capable of rapid movements rather than force. It is found in the coracoid vertex of the shoulder blade and its implantation in the anterior aspect, lower middle third of the humeral shaft.

It fulfills a function of balancer and collector.

Deltoid muscle

It is named after its resemblance to the Greek letter "delta." It is located in the upper arm and upper part of the shoulder.

It finds its origin in three well differentiated parts; the clavicle, the acromium, and the spinous process of the scapula. Its insertion is in the deltoid tuberosity on the lateral surface of the proximal humeral axis.

Its functions include shoulder flexion and internal rotation and extension of the shoulder.

Latissimus dorsi muscle

It is one of the longest and widest muscles of the shoulder girdle. It is a muscle in which all its fibers are ascending.

It finds its origin in a continuous line in all the spinous processes from the seventh dorsal vertebra to the crest of the sacrum, in the lumbar ligaments and in the upper area of ​​the crest of the sacrum. Its insertion is in a small spinal tendon in the infratroquinean zone and in the bicipital canal of the humerus.

It fulfills a function of retroversion or extension of the arm, at the same time as it performs internal rotation and approximation functions.

Sternocleidomastoid muscle

It is a long muscle on the side of the neck that extends from the chest to the base of the skull. It finds its origin in the mastoid process of the temporal bone and its insertion in the external manubrium, and in the upper part of the middle third of the clavicle.

Its function is the rotation of the head to the opposite side, lateral inclination and slight extension, cervical flexion and cranial extension.

Infraspinatus muscle

It is found in the infraspinatus fossa of the shoulder blade and its fitting in the trochiter, behind the supraspinatus muscle.

It fulfills the function of an external rotator, coaptador.

Omohoid muscle

It begins at the base of the coracoid tip and its attachment to the anterior horn of the hyoid bone (base of the tongue).

Pectoralis major muscle

It is a thick, resistant and wide muscle that covers from the shoulder to the sternum. A developed pectoralis major is more evident in men, as a woman's breasts often hide the pectoral muscles.

It finds its origin in the clavicular head and the sternum, its insertion is in the subtrochiterian ridge in a cross way.

As a function it is the most important muscle for adduction and anteversion of the shoulder joint.

Pectoralis minor muscle

It is covered by the pectoralis major muscle. It finds its origin in the coracoid tip of the shoulder blade and its insertion in the anterolateral aspects of the third, fourth and fifth ribs.

Its function is to bring the shoulder blade forward and down.

Teres Major muscle

It finds its origin in the lower part of the axillary edge of the shoulder blade and its insertion in the subtrochinean ridge, but lower than the subscapularis muscle.

It fulfills the function of adductor, internal rotator and extensor.

Teres minor muscle

It finds its origin in the upper axillary edge of the scapula and its fitting in the trochiter, behind the infraspinatus.

It fulfills the function of an external rotator.

Rhomboid minor and major muscle

It finds its origin in the entire vertebral edge of the scapula, except for its two tips and the minor has its insertion in the spinous processes of the last two cervical vertebrae, while the greater in the spinous tips of the last 4-5 dorsal vertebrae.

It fulfills the function of adductor and rotator of the shoulder blade, as well as the rotation of the scapula downwards and providing stability for the shoulder complex.

Serratus Major muscle

It is a muscle made up of 10 muscle bellies. It finds its origin in the same vertebral edge of the scapula, but through its anterior aspect and its insertion in the anterolateral aspects of the first 10 ribs.

Their function is to maintain a solid point of the shoulder blade, separation and rotation of the shoulder blade.

Subscapularis muscle

It finds its origin in the costal aspect, subscapular fossa of the scapula and its insertion in the anterior and middle part of the troquin.

It acts as an internal rotator, coaptador

Supraspinatus muscle

It finds its origin in the supraspinatus fossa of the shoulder blade and its insertion in the uppermost part of the trochiter.

It fulfills the function of an abductor. The abduction start begins, from 0º to 30º.

Trapezius muscle

It is a zonal skull muscle, occupying almost the entire center of the spine. It finds its origin along the nuchal crest of the occipital bone and the spinous processes of the cervical and thoracic vertebrae.

Its insertion is through the tendons in the clavicle, the acromion, and the spine of the scapula. It is responsible for moving, turning, and stabilizing the scapula (shoulder blade) and extending the head into the neck.

References

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