AC joint (sub)luxation
The acromioclavicular joint, also called the 'AC joint', forms the connection between the clavicle (collarbone) and the top of the shoulder blade. Dislocation of this joint can cause damage to the ligaments and capsules that stabilise the joint.
Injuries to the AC joint are common in cyclists and judokas. They are at increased risk of falling on the top of the shoulder. This is a classic cause of acromioclavicular dislocation (luxation).
Description of the condition
The clavicle is connected to the acromion via the AC joint. This is the top and outermost part of the shoulder blade. The joint is kept in position by ligaments. If these ligaments become damaged, this can result in acromioclavicular symptoms.
When the forces on the AC joint become too great, for example through an accident or a fall, this can cause ligament rupture. The clavicle is effectively dislocated.
Cause and origin
The injury is usually caused by a fall on the top of the shoulder or on an outstretched arm. This causes bruising of the surrounding tissues.
Signs & symptoms
The painful spot can often be pinpointed. Sometimes the symptoms can be provoked by pressing on or around the AC joint. The pain increases when the shoulder is moved forward, or when the shoulder hangs down. There can also be swelling.
As the AC joint is located directly beneath the skin, it is often clear in the case of a severe injury that the clavicle is not in the correct position. The clavicle juts upwards slightly and a clear 'step' is visible on the shoulder. Always compare the right and left shoulders in order to assess any abnormality.
The diagnosis is made according to the patient's story and a number of physiotherapeutic tests. Often the passive movement of the upper arm in front of the body towards the chest (horizontal adduction) is painful.
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