Acromioclavicular Joint - Injuries

Injuries

A common injury to the AC joint is dislocation, often called AC separation or shoulder separation. This is not the same as a "shoulder dislocation," which refers to dislocation of the glenohumeral joint.

AC dislocation is particularly common in collision sports such as ice hockey, football, Judo, rugby and aussie rules, and is also a problem for those who participate in swimming, horseback riding, mountain biking, biking and snow skiing. The most common mechanism of injury is a fall on the tip of the shoulder or FOOSH (falls on outstretched hand).

AC dislocations are graded from I to VI. Grading is based upon the degree of separation of the acromion from the clavicle with weight applied to the arm. Grade I is slight displacement of the joint, and a badly stretched or partially torn AC ligament. It has the normal separation of <4mm. Grade II is a partial dislocation of the AC joint with a complete disruption tear of the AC joint and a partial disruption of coracoclavicular ligament. The AC gap is >5mm. Grades I and II never require surgery and heal by themselves, though physical therapy may be required. Grade III is complete disruption of AC and CC ligaments. On plain film the inferior aspect of the clavicle will be above the superior aspect of the acromion. This can also be assessed with an MRI scan, which will also demonstrate disruption of the coracoclavicular ligaments (the degree depending on the severity of AC joint disruption) as well as tearing of the joint capsule. The joint will be very tender and swollen on examination. Grade III separations most often do not require surgery and shoulder function should return to normal after 16–20 weeks. However, there will be some physical deformity of the shoulder with a noticeable bump resulting from the dislocation of the clavicle. Grades IV-VI are complications on a 'standard' dislocation involving a displacement of the clavicle, and will almost always require surgery.