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Shoulder Anatomy

The Normal Shoulder

The shoulder is one of the most mobile joints in the body. It is a shallow ball and socket joint and as such, it requires a complex arrangement of ligament, tendons and muscles all working together to keep it in joint and moving correctly. This allows us to be able to move our arm around and position our hand exactly where we want it to perform everyday tasks without pain or discomfort

The Glenoid

This is the bony socket of the shoulder joint. As it is relatively flat, it has a cartilage covering which helps to deepen it into more of a socket shape. When shoulders dislocate, the bone edges and cartilage covering can become broken or fractured (Bony Bankart lesion). This can predispose to further dislocations.

Arthritis is seen when the cartilage covering becomes damaged or worn away. This could be related to wear and tear, overuse or previous injuries as we see with Osteoarthritis. Other forms of arthritis can be due to joint inflammation such as Rheumatoid arthritis. The inflammation in these cases leads to damage of the cartilage surfaces.

The Humeral Head

This is the ball part of the ball and socket shoulder joint and forms the top end of the humerus (arm bone). The humeral head can be damaged in dislocations and falls leading to fractures especially when the bone is weaker as is seen with advancing age (Osteoporosis).

Wearing of the cartilage on the humeral head can also lead to pain and stiffness as is seen with different types of arthritis.

The Rotator Cuff

This is a group of four muscles and their tendons (the part that attaches to the bone) which serve to keep the ball (humeral head) in the centre of the socket (glenoid) and allow the shoulder to move. These muscles are

Supraspinatus – the muscle on the top that helps lift the arm away from the side of the body

Subscapularis – the muscle at the front that allows you to twist your arm inwards and also reach up your back

Infraspinatus and Teres minor – the muscles at the back of the shoulder which allow you to twist your arm outwards.

Impingement occurs when these tendons catch on the bone at the top of the shoulder.

Furthermore these tendons can become inflamed (tendinitis) and or even torn through wear and tear or from injuries such as falls.


This is a small sac of fluid that sits on top of the rotator cuff tendons and beneath the bone at the top of the shoulder (the acromion). It acts to lubricate and ensure smooth movement of the tendons beneath the bony ceiling above. This area can become inflamed and lead to shoulder pain – Bursitis.

Injections are often performed into the bursa to reduce shoulder pain and help with physiotherapy and rehab.


This is a ring of tissue that surrounds the socket of the shoulder. It acts to make the shoulder socket deeper but also as an anchor point for the important ligaments that help to stabilise the shoulder and keep it in joint.

The labrum is often damaged/torn as a result of shoulder dislocations.

Acromioclavicular Joint (ACJ)

This joint is the link between the end of the collar bone (clavicle) and the top of the shoulder blade (acromion). It can be injured in falls and lead to dislocations where the bone ends become very prominent.

It is also prone to arthritis, especially in those people who have heavy jobs or those who have played a lot of overhead or contact sports.

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