North Hampshire Hospital
The Hampshire Clinic
Basingstoke, Hampshire, UK

Mr John Britton FRCS
Consultant Orthopaedic Surgeon

Information for patients undergoing orthopaedic treatment

 


Anatomy

To understand the disorders of the shoulder it is necessary to have a basic knowledge of the anatomy of the shoulder girdle. The shoulder is not a single joint but comprises a number of separate articulations:

  • Gleno humeral joint (true shoulder): The articulation between the upper arm (humerus) and the shoulder blade (scapula).

  • Acromio-clavicular joint: The articulation between the collar bone (clavicle) and shoulder blade.

  • Subacromial space: The interface between the rotator cuff and the shoulder blade.

 

Gleno-humeral joint

Although traditionally described as a 'ball and socket' joint the shoulder is a ball joint without a bony socket. As can be seen in the illustration the humerus articulates with a small flat area of the shoulder blade known as the glenoid, which is no larger than a 10p piece. There is no skeletal stability as there is in a hip, where the femoral head is held within a bony socket.

To maintain the stability the shoulder relies on a combination of ligaments, tendons and muscles. At the deepest level the humerus and shoulder are joined by a fibrous capsule; this structure is thickened into a 'labrum' where it attaches to the shoulder blade. Damage to the capsule or labrum may lead to recurrent dislocation or subluxation of the shoulder (click here to read about instability).

The socket in which the humerus is located is formed by a group of muscles known as the 'rotator cuff. These muscles arise from either side of the shoulder blade and form a hood in which the humeral head sits. The rotator cuff may be torn as a result of a fall; furthermore it is prone to spontaneous tears in older patients as a result of degenerative change in the tendons (click here to read more about rotator cuff disease).

The tendons of the rotator cuff move immediately under the acromium and this may cause irritation; this is a common cause of shoulder pain and is given the name of subacomial impingement (click here to read more about impingement).

The humeral head and glenoid are normally covered in articular cartilage, which provides an extremely smooth articular surface. Both rheumatoid and osteoarthritis cause erosion of the articular surface, which may necessitate joint replacement (click to read more).

Acromioclavicular joint

The collar bone articulates with the shoulder blade at the tip of the shoulder; this joint allows the shoulder blade to move over the chest wall. The acromioclavicular joint is often injured by falling directly onto the shoulder. It is also prone to developing osteoarthritic change.

 

J M Britton 2007

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