Shoulder Instability  

What is it?

The shoulder joint (gleno-humeral joint) comprises the top of the long upper arm bone (humerus) and the shoulder socket (glenoid) which is part of the shoulder blade (scapula). As a ball and socket joint, like the hip, you would expect it to be reasonable stable. However, whereas the hip joint has a deep socket which almost fully encapsulates the head of the femur (thigh bone), the shoulder ball and socket joint can be imagined like that of a basketball balancing on a teacup. In order to maximize stability in this very mobile of joints, there are many ligaments and muscles which act to draw the head of the humerus in to a nice close fit in the glenoid.
 

Instability can occur as a consequence of trauma or can happen over time. Traumatic instability is usually as a consequence of a fall which disrupts the soft tissue integrity of the shoulder joint. This is usually characterised by immediate pain and swelling and a great reluctance to want to move the arm in any direction. Commonly the shoulder will dislocate in an anterior (forward) direction and will require medical help to relocate the joint in the correct position.
 

Atraumatic (without trauma) instability results from excessive stresses and strains placed upon the joint capsule and soft tissues which, over time, gradually reduce the stability of the joint. Those individuals who partake in activities which push the shoulder joint beyond their normal range of movement repetitively such as gymnasts, cricket bowlers and swimmers can often experience increased joint laxity. Commonly, subluxations or partial dislocations are reported with the shoulder ‘giving out’ or ‘coming out of its socket’. Some individuals who are particularly flexible may have a condition which makes them hypermobile. There is often a family history of this, with other members of the family reporting dislocations or subluxations of the shoulder or other joints in the past.
 

Treatment

Traumatic instability as described above will often require a period of time in relative immobilization (usually a sling) in order for the soft tissue to heal in their correct position. Following this Physiotherapy is very important to ensure that the correct rehabilitation is performed at the right time scales for a full recovery to be achieved. It is imperative to adhere to post dislocation protocols as the recurrence rate for anterior shoulder dislocations in young men is over 90%.
 

Atraumatic instability also requires a specific rehabilitation programme which will usually involve progressive rotator cuff and scapula strengthening exercises in order to achieve improved stability. This will require close evaluation and correction of the postural and muscle imbalances which the body adopts to compensate for the instability.