AC Joint Injury
The acromioclavicular (AC) joint is a small joint of the outer aspect of the shoulder that is formed by the acromion and clavicle (collarbone).
In this case, MRI demonstrates increased fluid (blue arrow) within the joint, which is also separated, consistent with the diagnosis of a grade two sprain.
The coracoclavicular ligament (yellow arrows) acts as the main stabiliser of this joint and is of increased signal in this case in keeping with injury to this structure.
AC joint injury usually occurs following a fall onto the outer point of the shoulder and in most cases can be treated without surgery.
In the setting where the clavicle is completely offset from the acromion, surgical fixation is warranted in order to preserve function and to minimise pain in the long run.
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