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    2019
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Structure of the Shoulder Joint

Structure of the Shoulder Joint

Our shoulder is the most mobile joint in the body.  It is this flexibility of the shoulder that provides the upper extremity with tremendous range of movement that allows us to reach objects overhead as well as behind our back.Being a very mobile joint, shoulder requires considerable support from surrounding muscles and tendons to discharge its function seamlessly.  On the contrary, being a very flexible joint, shoulder is not as stable as some other joints in our body such as hip joint.  So there is no surprise that shoulder is prone to injury, dislocation and separation.  Apart from that, many people suffer shoulder-related symptoms such as arthritis, soft-tissue problems like shoulder bursitis and rotator cuff injuries.

The best way to make sure our shoulder joint is in pristine condition is to check if we go about our activities of daily living without worrying too much about our shoulder.  In this write-up, let’s have a look at the structure of the shoulder joint in detail.

Articulating surface:

Structurally, shoulder joint is formed by the articulation of the humeral head with the glenoid cavity of the scapula.  That is why shoulder joint is also called glenohumeral joint.  Like other synovial joint, articulating surfaces are covered with hyaline cartilage.  The humeral head is much larger than the glenoid fossa, enabling the joint to have a wide range of motion, but the inherent risk is instability.  In order to lessen this disproportion in surfaces, the glenoid fossa is intensified by a fibrocartilage rim, glenoid labrum.

Though people generally think shoulder as a single joint, the shoulder actually has four joints:

Glenohumeral joint:  This is what commonly referred to as shoulder joint.  It can be called the primary joint of the shoulder, where the rounded top or head of the humerus nestles into a rounded socket of the scapula, called the glenoid.  The ball-and-socket facilitates the circular movement of the arm.  Unlike the hip joint, where humeral head fits inside a socket of the pelvis, in shoulder, the glenoid is too small and shallow for the humeral head to go inside it.  So the rounded humeral head glides against the cuplike glenoid.

Acromioclavicular joint:  The acromioclavicular joint is located where the collarbone (clavicula) slides along the scapula’s acromion.  The acromion is situated at the peak of the scapula.  It is an irregular, somewhat flat, triangle-shaped bone.  The acromioclavicular joint facilitates rising the arm over the head.

Sternoclavicular joint:  It is located where the clavicle meets the sternum at the top of the chest.

Scapulothoracic joint:It is located where the scapula glides against the thoracic ribcage at the back of the body.  However, no ligaments connect the bones at this joint. 

Shoulder joint anatomy:

The shoulder is located at the meeting place of arm and torso.The shoulder joint (glenohumeral joint) is a ball-and-socket joint between the scapula and the humerus. The shoulder consists of the following basic components to discharge its duties.

Shoulder bones:  In order to glide against each other, bones must be strong and surface must be smooth.  This function of the shoulder may be impaired and pain can be felt if there are bony growths called osteophytes or bone spurs.

Shoulder cartilage:Cartilage must also be strong and smooth in order to facilitate the movement of bones without too much friction.

Shoulder muscles:  Duty of the muscles is to support the joints and enable movement.

Shoulder ligaments and tendons:  There are multiple ligaments and tendons around the shoulder.  They must also be strong to bind the shoulder joint together and encapsulate them in a tough but flexible structure.  It is the ligaments connect bones to bonesand tendons that connect bone to muscles.  Movable parts in the shoulder joint are encased in these tendons and ligaments.  These tissues provide support for the stability of the shoulder joint while allowing for full range of movement.

If any one of the above-mentioned components loses its vigor or in some way irritated or compromised, shoulder problems will occur.  The principal cause is overuse (as we age), dislocation, accident such as using arms to cushion a fall, shaking the shoulder joint vigorously.

Have you ever thought how your shoulder joint works?

Let’s see how this amazing joint that provides extreme flexibility works.

The place where the bones meet is covered with articular cartilage, a smooth white tissue material.  Articular cartilage enables two bone surfaces to glide against each other.  It also works as a shock absorber, cushioning bones against getting into contact with each other.  It should be understood that when the articular cartilage is thinned or damaged, its ability to reduce friction between bones and soften an impact is reduced.

A strong piece of cartilage, called the labrum, rings the outer edge of the glenoid.  Labrum makes the shoulder joint stable and its elasticity allows flexibility.Rotator cuff muscles extend from the scapula to the humeral head, stabilizing the shoulder joint by keeping the humeral head to the glenoid.  There is also a fluid-filled sac called bursa around the shoulder joint that helps the muscles and tendons slide freely as the shoulder moves.

Synovial membrane encapsulates the shoulder joint.  Synovial membrane produces synovial fluid.  It is the duty of this thick, viscous fluid to lubricate and circulate nutrients to the joint.When the shoulder is at rest, synovial fluid is contained in the cartilage, much like water in a sponge.  When the shoulder is in motion or lifts weight, the synovial fluid is squeezed out. Sosynovial membrane is necessary to keep the joints lubricated and healthy.

To sum up, the shoulder joint is an outstanding combination of strong cartilages and muscles, tendons, flexible ligaments and strong bones.  It is extremely flexible, providing a wide range of movement.  However, this complex structure is prone to wear and tear over time, so shoulder symptoms should not be given cold shoulders.

For enquiries related to Shoulder Injuries and Shoulder Pain, send a message to www.BangaloreShoulderInstitute.com/contact

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