Dislocation Of The Shoulder Joint

Published: 04th December 2009
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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.

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.

Dislocations backwards are not common and due to force applied to the arm when it is over the body and turned inwards, with epileptic seizures and electrocution being possible causes as the big chest and back muscles pull the joint out due to spasms. The joint can also dislocate downwards if the arm is moved outwards and sideways with excessive force, levering the joint out against the part of the shoulder blade above it. This type of injury needs careful monitoring as it is more likely to be associated with other soft tissue injuries such as nerve injury, damage to the blood vessels and tears to the rotator cuff muscles.

Dislocation can occur without trauma and in these cases the shoulder instability is often in all directions and more likely to occur in people who are hypermobile in their joints. This is known as multidirectional instability and is more common in younger people under thirty years old, occurring in both shoulders and tending to run in families. The joint problems may start with a subluxation which is a partial dislocation where the joint surface moves off the other one to some degree then snaps back again. Some people can dislocate their joint voluntarily and this may be connected with psychiatric difficulties in these patients.

Anterior shoulder dislocation typically shows by a patient holding their arm slightly to the side and turned outwards, with a palpable anterior bulge due to the humeral head sitting to the front of the shoulder. Muscle spasm around the shoulder can be powerful and severe pain results from attempting to move the joint. A backwards shoulder dislocation forces patients to hold their arm in close to the body and rotated inwards, with the head of the arm bone felt at the back. Misdiagnosis as frozen shoulder has been recorded.

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.

Shoulder dislocations are usually extremely painful and the medical management of pain relief has many options to optimise the ease of reducing the joint dislocation. If the dislocation has been present for a shorter time it is easier to relocate without the help of narcotic drugs or stronger muscle relaxation medication. Sedatives are useful and best if they act quickly, provide good relaxation of the muscles and lose their effect quickly to facilitate recovery. On reduction the aftercare for the joint is to use a sling for up to three weeks to allow the healing of the capsule.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about physiotherapy, physiotherapy, physiotherapists in London, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.

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