Shoulder dislocation

A shoulder dislocation may occur as a result of a fall onto an outstretched hand, direct trauma or blow to the shoulder, violent tugging of the arm, electrocution or epileptic fits or secondary to excessive ligamentous laxity of the body. The commonest direction for the dislocation is anterior (where the humeral head comes out to the front of its socket).

Anterior shoulder dislocation is quite common especially in the young and active, and has a high incidence of recurrence (when a dislocation occurs repeatedly it is called instability) - the younger the age of the dislocators, the higher the rate of recurrence. Patients within the age of 20-30 years old has a 80-90% chance of getting repeated episodes of dislocation in the same shoulder.




X-ray of the right shoulder showing a normal shoulder (left) and a dislocated shoulder (below).

Anatomy. The shoulder joint, right picture (medically termed the glenohumeral joint) is essentially an articulation between the humerus (arm bone) and the glenoid (part of the shoulder blade). The size of the humeral articular surface (bigger and rounded in shape) is disproportionate to the size of the smaller and flatter glenoid surface. Without the supporting soft tissues (namely the ligaments and muscles), the shoulder is inherently unstable, just like a golf ball on a tee, (lower left picture). Another stabilizing structure is the labrum, which deepens the glenoid surface (lower right picture).












So why don't we dislocate our shoulder every now and then? It is because of the supporting structures - the ligaments and the muscles that envelope and maintain the humeral head within the glenoid cup which is further deepened by the labrum. When a person dislocates his shoulder, these structures are usually damaged or torn.

Management is initiated by taking a full history, examining the affected shoulder and upper limb (anterior dislocation may injure the axillary nerve which supplies the deltoid muscle - which functions to raise the arm above the shoulder and supplies the sensation at the middle of the shoulder (the so-called 'regimental badge' area), and performing certain maneuvers to reduce the shoulder back into its socket. Reduction must be done as soon as possible as dislocations will distort the blood supply to the humeral head and may cause long-term problems to the patient. Once reduced, the shoulder will be supported in a sling (picture) for 2-4 weeks after which physical therapy will be initiated. The aim of physiotherapy is to strengthen the muscles around the shoulder and to gain back the normal motion in the affected shoulder.

Most patients respond well to conservative treatment. However, patients with persistent instability (either having repeated dislocations or being apprehensive that the shoulder might 'pop-out' during routine activities or those experiencing pain during certain 'vulnerable' positions) may need to undergo surgery to stabilize the shoulder.

For further information, please consult your doctor.