Dislocation of a joint means that the joint surfaces, which are normally closely applied to each other, are completely disrupted and do not touch each other any longer. The joint capsule surrounds the joint and supports it and is often damaged as the joint surfaces move apart from their normal position. Dislocations may also result in damage to the joint surfaces themselves as they move across each other in their journey to the dislocated position. Joint, ligament and nerve injuries can occur during dislocations .
Dislocations of the shoulder are the most common form of dislocation of a joint, making up almost half of all of this type of injury. The commonest form of dislocation is for the humeral head to be displaced forwards, known as an anterior dislocation . This occurs most often when the arm is out to the side, rotated externally and moved backwards and there is a forwards force on the upper arm, pushing the joint out in its position of vulnerability. A blow to the rear of the arm, a fall on an outstretched hand (FOOSH) and a strong outward rotation plus shoulder abduction can all result in a dislocation .
Posterior shoulder dislocation is not frequent and occurs with the arm turned inwards and across the body, most often caused by muscle spasm in the large back and chest muscles from an epileptic fit or an electrocution event. A downward joint dislocation can occur if the arm is moved outwards and rotated outwardly with significant force, the arm bone levering against the underside of the shoulder blade and so pushing the joint out of place. The posterior dislocation is more commonly associated with side effects such as damage to the nerves and blood vessels or an injury to the shoulder rotator cuff muscles.
An atraumatic shoulder dislocation can occur with a tendency for the joint to be unstable in every direction, often present in patients with joint hypermobility. Multidirectional instability is the medical term given to this syndrome which presents in families, in younger people of less than 30 years and occurs in both shoulders. Subluxation of the joint can occur initially which involves one side of the joint coming off its opposite number to a degree and then relocating suddenly into position. Shoulders can be dislocated voluntarily in some cases, although this may normally be connected with psychiatric disorders.
Patients who have anterior shoulder dislocation typically have their arm slightly out to the side and rotated outwardly, with an obvious bulge of the head of the humerus easily felt at the front of the shoulder. The shoulder muscles may be in spasm and any attempt to move is likely to cause extreme pain. Posterior shoulder dislocations make a patient keep their arm inwardly rotated and kept in to the side of the body and the humeral head can be felt posteriorly. This kind of injury can be missed or misclassified as frozen shoulder.
The relocation of a shoulder dislocation is performed by surgeons in many different ways and the time from the incident to when the joint is finally relocated is the important matter. If the time is too long the muscle spasm increases and interferes with fixing the dislocation . An original way was to put a foot in the person’s axilla to make one end secure and traction the arm lengthways until the reduction is effected. Techniques have developed and an effective modern way is to abduct the shoulder whilst pushing the humeral head anteriorly, then rotate the arm externally and traction the arm, leading very often to success.
A significant part of a shoulder dislocation is pain and doctors have many ways of ensure the best pain relief and make the reduction process as easy as it can be. If the dislocation is recent then the joint may be relocated without much in the way of analgesics or muscle relaxing drugs. The best sedatives used have a fast mode of action, good muscular relaxation properties and short duration of action so the patient recovers quickly. Once relocated the arm should be placed in a sling which may be retained for up to three weeks to allow the capsular tear to heal.