Dislocation of the Shoulder

By Jonathan Blood Smyth

A joint dislocation occurs when the two joint surfaces, which normally sit in intimate contact with each other, are wrenched away from each other to lie apart without any relationship. Joints have a surrounding ligamentous bag called a joint capsule and this can be typically injured as the surfaces force their way past each other. The surfaces of the joints themselves can be damaged as they hit each other on the way to becoming dislocated. Other injuries which can occur include damage to the local nerves and ligaments.

Of all joint dislocations, shoulder dislocations are the most common, making up almost half the total number of this kind of joint injury. An anterior dislocation, with the head of humerus coming off the shoulder socket to the front, is the most common form of this condition. The most usual position for the shoulder to dislocate in is when there is a force applied to the back of the arm with the arm in an outwardly rotated, extended and abducted position. Less commonly a blow to the back of the arm might do it, or a fall on the hand or just moving the arm forcefully outwards and rotating it externally.

A posterior dislocation is uncommon and secondary to a stress on the arm when it is inwards across the body and inwardly rotated, with the large back and chest muscles sometimes pulling the joint out of its socket. This can occur if someone is electrocuted or if they have epileptic seizures, both of which can cause muscle spasms. The shoulder can dislocate downwards if there is a very forceful movement of the shoulder outwards and sideways, with the joint being levered out over part of the scapula above. This sort of dislocation should be closely monitored as complications of the injury are common with nerve damage, blood vessels injury and rotator cuff tears.

There may be no trauma in some cases of shoulder dislocation and instability of the shoulder may occur in all joint directions, typical presenting in patients who have hypermobile joints. This condition is called multidirectional instability and tends to happen in both shoulders, run in the family and be in younger people under thirty. A joint subluxation is often the start of these problems, where the joint slips partly off its partner to an amount and then clicks back into place. An ability to voluntarily dislocate the shoulder can occur, perhaps related to psychiatric difficulties in this group of people.

The presentation of anterior dislocation of the shoulder is for the patient to hold their arm rotated outwards and slightly to the side, the arm bone head easily felt at the front of the joint. The shoulder muscles may be in a powerful spasm and trying to move the shoulder results in high levels of pain. A dislocation of the shoulder posteriorly shows itself by the patient keeping the arm close to the body and turned inwards, the head of the humerus being palpable at the rear of the joint, although this condition has been misdiagnosed as frozen shoulder.

Reduction of a shoulder dislocation can be performed in a large number of techniques but it is the time from dislocation to when the shoulder is relocated which is important. As the time increases the muscle spasm becomes more severe, making reduction more difficult. An old technique is to place the foot in the armpit to provide stability and pull the arm lengthways until the joint goes back into place. Less traumatically the upper arm can be moved away from the body and the head of the humerus pushed forwards. Once the shoulder reaches 90 degrees the arm is turned outwards and traction applied.

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. - 32188

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