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ACJ Instability/Dislocation

The clavicle (collar bone) has powerful muscles attached to it that constantly apply an upward force on it. In order to maintain the AC joint in place, these forces are opposed by strong ligaments and a capsule.

There are 2 groups of ligaments: those that span the AC joint (from clavicle to the acromion) and those from the coracoid (a bone from the shoulder blade under the clavicle) to the under-surface of the clavicle.

Instability of the AC joint occurs as a result of an injury. This is usually a direct fall onto the shoulder, but can also happen when there is a pulling or a pushing force on a straight arm, for example if involved in an car accident with the hand on the steering wheel.

Significant injury to the ACJ can result in a sprain, a subluxation or complete dislocation. In dislocations, all the above ligaments are torn causing the clavicle to displace, commonly upwards but can be backwards or very rarely downwards.


Pain is the main symptom. This may be constant but is usually worse with overhead movement. There is an obvious deformity.

If this is treated without surgery, the pain may settle down but this can take several months. The more severe the injury/displacement, the more likely that the pain will persist.

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