The Shoulder - Structure & Function
Structure:
The shoulder is a ball and socket joint between the humeral head and the glenoid on the shoulder blade. The structure of the shoulder joint can be compared to a golf ball perched on a golf tee. The acromio-clavicular joint between the outer end of the clavicle and the acromion is a neighbouring joint that is regarded as part of the shoulder on the basis of its proximity and symptoms. This joint connects the shoulder complex to the chest via the clavicle and therefore to the trunk. The scapula is connected and supported by muscles to the back of the chest wall and spinal column.
Function:
The shoulder joint is the most mobile and versatile joint in the human body. This joint has developed in response to the upright stance of human beings who stand on two legs. They use their upper limbs to manipulate their environment. The shoulder therefore has to provide a stable and pain free platform for humans to be able to use their hands in space. The shoulder joint is not designed for nor is it capable of load bearing for prolonged periods. It relies on the specialised soft tissues surrounding it to provide stability when force is transmitted across the joint. These supporting and stabilising structures work using either dynamic or static methods. The dynamic structures are muscles that principally arise from the scapula and together form the rotator cuff. There are secondary muscles that together stabilise the scapula on the back of the chest wall. The static structures are mainly the capsule of the shoulder which is thickened in specific areas and are called ligaments.
