Typical mechanism of injury as well as tenderness and swelling or a clear malposition at the acromioclavicular (AC) joint raise the suspicion.
There are many different types and severity grades which may be challenging to tell from each other.
The diagnosis is confirmed by x-ray. AP projection may misleadingly seem almost normal: axillary projection is recommended.
The treatment is either conservative or operative according to the type of injury.
Aetiology
Usually caused by falling on the shoulder whereupon the upper extremity is jerked downwards.
Common findings
Local tenderness, oedema or malposition around the AC joint
The dislocated head of the clavicula is often felt as a prominence and it is sometimes - depending on the severity of the injury - unstable in which case it is possible to press it downwards or move it in horizontal direction.
Investigations
An x-ray is taken to confirm the diagnosis and to assess the severity grade of the injury. The examination is performed without loading so that both AC-joints are visible. An axillary projection is to be recommended.
Findings and treatment according to the injury grade
Rockwood classification of acromioclavicular (AC) joint dislocations: see picture 1.
Grade 1 luxation
The joint is locally painful and tender when palpated but the findings in the x-ray are normal or only minimally abnormal.
Immediate mobilization of the limb as much as the pain allows, gradually increasing the loading during the weeks after the injury
Grade 2 luxation
X-ray shows a slight upward dislocation of the clavicula (less than its diameter) and a slight widening of the AC joint.
An arm sling (mitella) is worn for about one week to manage the pain, and after that, mobilization of the shoulder joint as after grade 1 luxation.
Grade 3 to grade 6 luxations
The ligaments of the AC joint and - in more severe cases - also other stabilizing structures around the joint are injured.
The joint is unstable when palpated, and a so-called ”piano key” phenomenon is observed in the clavicula, and/or the bone is unstable in horizontal direction.
In the x-ray, the clavicula is lifted upwards as much as it is thick or more, and the gap between the clavicula and the coracoid is often considerably widened.
In a grade 4 luxation, the dislocation takes place in horizontal direction, whereupon an AP x-ray may be almost normal. The diagnosis is based on clinical examination where attention is paid to the horizontal instability of the clavicula, and on the axillary projection of the shoulder joint the x-ray.
The majority of grade 3 injuries may be treated conservatively. It may be challenging to differentiate grade 4 to grade 6 injuries from grade 3 injuries; they require surgical assessment because the decision concerning the line of treatment is based on assessment of activity, for example, and other patient-specific matters.