GLENOHUMERAL JOINT: FUNCTIONS, ANATOMY, PLANES AND AXES - ANATOMY AND PHYSIOLOGY - 2024

The glenohumeral joint is made up of the humerus, arm and shoulder blade or dorsal scapula bones, corresponding to the insertion of the head of the first in the glenoid cavity of the second. The relationship between these surfaces resembles a ball inside a wide-mouthed, spheroidal, and multiaxial cup; for this reason it has great mobility.

It is also known as the scapulohumeral joint. It integrates the joint complex of the shoulder, called the shoulder girdle, where the sternoclavicuar and acromioclavicular joints are also located. Cartilaginous structures, ligaments and joint capsule, and other muscular elements intervene in the stability of the scapulohumeral joint.

The integration of these four components is necessary to keep the joint together and functional. The glenohumeral joint is the main joint of the shoulder, whose range of motion offers countless advantages to the human being. Its main function is to give mobility to the entire upper limb.

The study of this joint is of interest in medicine, physiatry and occupational health. It is the most mobile and useful joint for man but, despite being stable, it can suffer dislocations with relative ease.

Shoulder joint injuries can imply disability, limiting physical and work activity to a variable degree.

Features

One of the joints with the greatest variety of movements is the glenohumeral joint. This has allowed man to carry out countless activities thanks to the use of the upper limbs. The hand, the extremity of the upper limb, is directed by the movement of the shoulder joints.

The function of the glenohumeral joint - and, consequently, of the shoulder - is defined by the seven movements it performs:

- Flexion.

- Extension.

- Adduction, when the limb is brought towards the body's midline.

- Abduction, when the limb is separated from the midline.

- External rotation, which occurs with the elbow at 90 ° and directs the arm outward on the long axis of the humerus.

- Internal rotation, movement opposite to external rotation.

- Circumduction, irregular movement that combines flexion, extension, adduction and abduction; Due to this, it promotes a circular movement, whose center is the shoulder joint.

These movements allow humans to write, drive cars, operate machinery, or play sports such as tennis, climbing, and swimming.

Anatomy

The glenohumeral joint is not made up of just the scapula and humerus. Various elements intervene in its architecture that make joint and joint functioning possible.

Joint type

It is a diarthrodial joint; that is, two bony surfaces joined, with a wide range of motion and stability. Arthrodial joints consist of the synovium, ligaments and joint capsule, which allow their mobility.

The synovial membrane, which lines the bone surfaces in contact, produces synovial fluid that acts as a lubricant.

The glenohumeral joint is often known as the ball-socket or ball-socket joint, due to the association of their joining surfaces. Within the diarthrodias, the glenohumeral joint corresponds to an enarthrodia, due to the seven movements it can perform.

Bones

Specifically, the glenohumeral joint is made up of two bones:

Scapula or shoulder blade

Flattened and triangular in shape, it is located on each side of the upper portion of the back. It forms the posterior part of the shoulder girdle, articulating with the clavicle, humerus and thorax.

The scapula has three angles, namely: inferior, internal and external. It is in the external angle where the coracoid process and the glenoid cavity meet, where the humerus articulates.

Humerus

Long bone located in the arm. It has bone structures that allow its articulation and attachment to the scapula: a hemispherical head, a neck, and the greater (troquiter) and lesser (troquín) tubercles, where the scapular muscles are inserted.

The joint of the body and humeral head is called anatomical neck, and fractures are more frequent there. Only a quarter of the head of the humerus has contact with the glenoid fossa, thus requiring support structures when articulating.

Ligaments

Four ligaments are responsible for stabilizing the joint and protecting it from the movements it performs: the superior (LGHS), middle (LGHM) and inferior (LGHI) glenohumeral ligaments, as well as the coracohumeral ligament. Due to their nature, these ligaments are passive elements of the joint.

Glenohumeral ligaments

The LGHS goes from the scapula to the lesser tubercle, the LGHM arises from the glenoid rim to insert on the inner side of the lesser tubercle, and the LGHI goes from the glenoid fossa and rim to the surgical neck of the humerus.

Consequently, the glenohumeral ligaments support inferior translational movements when adducting, externally rotating, and anteroposteriorly translating the humeral head, respectively.

Coracohumeral ligament

It goes from the outer edge and base of the coracoid process of the scapula to insert into the greater tubercle. Determines the attachment of the head of the humerus to the joint, acting as an anteroposterior brake. Other functions are unknown.

Glenoid impeller or labrum

It is a cartilaginous structure located on the edge of the glenoid cavity; It is ring-shaped and its function is to increase the contact surface of the humerus head, in addition to providing joint stability.

Joint capsule

The capsule is a connective tissue structure that surrounds the bony surfaces of the glenohumeral joint. It is divided into two portions: an external or fibrous one, and an internal one, or synovial membrane, which helps with joint lubrication.

This capsule also has spongy structures on its surface: bursae. These dampen the effects of mobilization of the joint. The subacromial bursa is the one that provides the greatest support due to its extension.

The external portion of the capsule is inserted in the anatomical neck of the humerus, while internally its insertion is in the labrum and glenoid cavity. The glenohumeral joint capsule, however much it covers the joint, is the structure that provides the least stability.

Muscles

The musculature that is related to the glenohumeral joint has a double function: stability and joint mobility.

An important muscular structure is the rotator cuff, made up of the supraspinatus, infraspinatus, teres minor, and subscapularis; their joint action keeps the humeral head within the joint.

Supraspinatus

It is inserted from the supraspinatus articular fossa to the superior facet of the humeral trochiter. It participates in the rotation and abduction of the arm, in conjunction with the deltoid muscle.

Infraspinous

It originates from the scapular infraspinatus fossa to insert into the medial facet of the humeral trochiter. Its action is to externally rotate the arm.

Minor round

It runs from the upper portion of the outer edge of the scapula to the lower facet of the trochiter. Participates in the actions of the rotator cuff and external rotation of the arm.

Subscapular

It goes from the subscapular fossa to the humerus tube. Contributes to adduction and internal rotation of the arm.

In addition to the rotator cuff, other muscles related to joint movement are:

Deltoid

It joins the deltoid tuberosity of the humerus with the scapular spine, acromion and external third of the clavicle, presenting three portions: anterior, middle and posterior.

It promotes movements of flexion and internal rotation of the arm with its anterior portion, abduction of the arm with its middle portion, and external rotation and extension with its posterior portion.

Major round (teres major)

It runs from the posterior aspect of the inferior angle of the scapula to the intertubercular groove of the humerus. Adducts and internally rotates the arm.

Planes and axes

The glenohumeral joint is a diarthrody with a wide range of movements, performing them in all three planes and three body axes. The different actions or joint movements are studied by biomechanics, and largely determine the mobility of the shoulder.

There are three planes that correspond to the movements of the joint: frontal plane, sagittal plane and transverse plane.

The axes of movement are also three: craniocaudal, lateral and anteroposterior. Hence the different actions of the arm on the shoulder:

- Flexo - extension, both in the frontal plane and in the sagittal plane. When it occurs in the frontal plane, it occurs on the lateral axis; in the sagittal plane the corresponding axis is the anteroposterior.

- Abduction and adduction, in the lateral plane and anteroposterior axis.

- External and internal rotation, in the transverse plane and craniocaudal axis of the humerus.

- Circumduction which, because it is a combination of movements, involves the three planes and axes.

The shoulder joint -especially the glenohumeral- allows the man to perform countless activities, his physical development and independence.

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