The shoulder joint, also known as the glenohumeral joint is a ball and socket joint. It is made up of the head of the humerus and the glenoid fossa of the scapula (the top of the upper arm and the side of the shoulder blade). The shoulder joint is one of the most freely moveable joints in the body. It is able to flex, extend, abduct, adduct and circumduct. This freedom of movement combined with the head of the humerus being relatively large compared to the socket, means the shoulder joint is inherently unstable. To increase this stability, the shoulder is supported through this movement by different tissues. These tissues include: ligaments, the labrum and muscles including the rotator cuff. The rotator cuff is a group of 4 muscles that work together to actively stabilise the shoulder joint. They also help to centralise the ball part of the joint on the socket as the shoulder moves through its full range. The muscles that make up the rotator cuff are the supraspinatus, infraspintaus, teres minor and subscapularis.


The smallest of the the rotator cuff muscles is the supraspinatus. The supraspinatus sits on the supraspinous fossa of the scapula. This is located on the back of the shoulder blade above the spine of the scapula. The muscle then runs laterally along the top of the scapula and runs underneath the acromion through the sub-acromial space (we will go in to more detail on this area later on). The tendon of supraspinatus then inserts on to the greater tubercle of the humerus. This allows the muscle to assist in abduction and some external rotation of the shoulder joint. Another key role it plays is depression of the head of the humerus in the glenoid fossa. This keeps the ball part of joint centralised in the socket throughout movement.


The infraspinatus is a thick triangular muscles that sits on the infraspinous fossa. This is also located on the back of the shoulder blade but sits underneath the spine of the scapula. The infraspinatus also runs laterally through the sub-acromial space and attaches on the the greater tubercle of the humerus. It is the main external rotator of the shoulder joint and also plays a role in stabilising the shoulder through movement.

Teres minor

The tires minor is a narrow muscle that sits below the infraspinatus. It originates from the upper two thirds of the lateral border of the scapula and also inserts in to the greater tubercle of the humerus, below the attachment of the infraspinatus. Similarly to the infraspinatus it is an external rotator of the shoulder and assists in the stabilisation of the joint through movement.


The subscapularis is a large triangular muscle that sits on the front of the scapular. It originates in the subscapular fossa of scapula and runs laterally across the front of the shoulder. It inserts in to the lesser tubercle of the humerus. The main function of the subscapularis is internal rotation of the shoulder joint. Similar to the rest of the rotator cuff muscles it also plays a role in stabilising the shoulder joint through movement.

What is rotator cuff related shoulder pain?

Rotator cuff related shoulder pain is an umbrella term that features a variety of conditions including:

  • Rotator cuff tendinopathy overload of a rotator cuff tendon (the soft tissue that connects muscles to bone), causing shoulder pain, inflammation and sometimes stiffness.
  • Partial and full-thickness rotator cuff tears – Tearing of the fibres of the muscle or tendon. This can be from an acute injury or can be degenerative.
  • Sub-acromial impingement – The sub-acromial space is occupied by the tendons of supraspinatus and infrapsinatus as well as the sub-acromial bursa. These structures are located between the head of the humerus and the inferior surface of the acromion. This condition describes the narrowing of the space due to different factors including inflammation of the bursa or tendons.

Rotator cuff related shoulder pain accounts for around 50%–85% of diagnoses for shoulder pain.

It is characterised by symptoms that include:

  • Pain– May or may not be present. Can be localised to anterior / lateral aspect of the shoulder, with referred pain down the upper arm (lateral aspect).
  • Painful range of motion
    • Painful arc (degrees vary – generally above shoulder height)
    • Painful external rotation / internal rotation / abduction
  • Muscle weakness – Weakness in the shoulder joint (particularly abduction and external rotation)
  • Functional impairments– Difficulty lifting, pushing, overhead movements and movements with hand behind the back.

Common causes

Repetitive movements – Tissues like tendons and bursa in the shoulder can become overloaded through repetitive movements. These can be sport or occupational related that can cause strain to these structures. This usually occurs as a result of overhead movements like swimming, decorating etc.

Acute injury – These can include incidents like falls, lifting heavy objects or sporting movements. These cause a force that is above the capacity of tendons and muscles which can lead to tears.

Sudden increases in load – A change in a training plan or a new physical job can both suddenly increase the amount of use the shoulder gets. This sudden change in load can cause irritation of tissues that don’t have the capacity to withstand its new tasks.

Lifestyle factors – These are not a direct cause of this type of injury can lead to an increased risk of developing it. These can include diabetes, hypothyroidism (under active thyroid), smoking, obesity, physical inactivity, high levels of fatty and processed foods in the diet.