The Shoulder

How it Works

The shoulder has the largest range of movement of any joint in the body.  The shoulder blade moves on the chest wall.  The humerus (arm bone) forms a ball and socket joint with the shoulder blade. The ball, or head of the humerus, is quite large and the socket relatively small and shallow.  The head is stabilised in the socket by the rotator cuff.

Postural Control
 

The shoulder blade floats freely in a sling of muscle from the chest wall, apart from the strut of the collarbone which comes off the sternum anteriorly.  Minor or major injury can upset the brain’s automatic control of the shoulder blade on the chest wall.  A longstanding focus of irritability in the shoulder in particular can prevent the brain from providing the normal support for the postural muscles. 

Impingement
 

Injury or fatigue of the rotator cuff muscles can lead to poor control of the humeral head and wear of the supraspinatus against the acromion.  This is appreciated as pain over the outside of the shoulder through an arc when the arm is loaded away from the body.  Repetitive use of the arm at and above chest height is a common cause.

The cornerstone of treatment of this condition is to understand the mechanics and avoid loading the arm with the elbow away from the body.

Rotator Cuff Tear
 

Injury or fatigue of the rotator cuff muscles can lead to poor control of the humeral head and wear of the supraspinatus against the acromion.  This is appreciated as pain over the outside of the shoulder through an arc when the arm is loaded away from the body.  Repetitive use of the arm at and above chest height is a common cause.

Arthritis
 

There are many types of arthritis. The three most common are osteoarthritis, post traumatic arthritis, and cuff tear arthropathy:

Primary osteoarthritis of the shoulder results from slow degenerative change in the shoulder joint, and is related to the ageing process. Over time cartilage on the joint surface becomes roughened and loses its lubrication properties.

Frozen Shoulder
 

Frozen shoulder is a common condition which can occur in middle age.  Its cause is unknown but interestingly it is more common in diabetics.  It causes the normally loose bag that holds the ball in the socket to become inflamed and thickened.  This results in severe pain as the bag is stretched with movement towards the end of range.  The process leads to progressive stiffening of the shoulder

Trauma
 

Shoulder Trauma is a common occurrence in young people who participate in an active sporting lifestyle, as well as during everyday life as the result of accidental injury. A broad spectrum of injury patterns can occur. These may be minor, in which case simple pain relief and physiotherapy can be of great benefit, or they can be major and require surgery to get the best result.

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