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Shoulder Joint Dislocation

A joint dislocates when the two parts of the joint, usually sitting in close contact with each other, are torn apart and then remain apart without being in the close relationship they were anymore. Surrounding a joint is a bag of ligamentous tissue called the joint capsule which is torn when the joint surfaces are forcibly moved past each other. The joint surfaces can be injured as their hard edges move against each other during the process. Typical other damage can be nerve, further joint and ligament injury.

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.

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.

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.

Several techniques are used to reduce a shoulder dislocation and the time it takes for the reduction to be performed is important. The muscle spasm can increase in severity and make the restoration of the normal joint alignment increasingly difficult. The oldest technique is to pull firmly on the arm whilst putting the foot in the armpit to give counter pressure. A more modern technique which is less traumatic is for the surgeon to move the arm bone outwards whilst pressuring the humeral head with their hand. Once the arm is at a right angle out to the side the arm can be tractioned and turned outwards, often leading to the joint being relocated.

Pain is a major presentation problem in shoulder dislocation and there are many alternatives that the medical staff can apply to give good pain relief and ease the process of reduction. A recent reduction can be moderately easily relocated in the absence of strong painkillers or muscle relaxants. The most useful sedative drug will have a quick onset of action, be able to supply good muscular relaxation and with an action which goes off quickly to allow rapid recovery. After the joint is back in place a sling is used for up to three weeks to allow the capsular damage to heal.


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