ACJ Injury (Acute)

An acute acromioclavicular joint (ACJ) injury is a sprain or dislocation of the joint between the clavicle and acromion, usually from a direct blow to the point of the shoulder.

It is common in contact sport, cycling and falls, and young men are most often affected. The Rockwood classification (types I to VI) guides management:

• •Types I and II: managed without surgery; most improve over 2 to 6 weeks
• •Type III: debated; an initial non-operative trial is usual in the UK
• •Types IV to VI: urgent orthopaedic assessment, often managed surgically

The ACJ is a planar synovial joint between the distal clavicle and the acromion. Its stabilisers are:

• •The AC capsule and ligaments, especially the superior part: the main restraint to horizontal (front to back) translation
• •The coracoclavicular (CC) ligaments, conoid (medial) and trapezoid (lateral): the main restraint to vertical translation
• •The deltotrapezial fascia, the anterior deltoid and trapezius attachments, which is torn in high-grade injuries

The usual mechanism is a direct blow to the point of the adducted shoulder. A fall on an outstretched hand is less common. Types IV to VI follow high-energy injuries such as road traffic collisions, cycling crashes and falls from height.