One of the most common shoulder injuries, acromioclavicular joint (ACJ) dislocations account for around 9% of shoulder girdle injuries

Usual cause is a direct blow to the superior aspect of the shoulder forcing the scapula down and leading to damage to to the AC and coracoclavicular (CC) ligaments – see diagram.

This is injury is more common in

• males
• athletes (especially full contact)
• ages between around 20-40

It is classified Grade I-VI (Rockwood classification) with I representing a sprain with no radiographical signs and V&VI significant displacement of the clavicle.

Examination

• The patient will express pain at the ACJ and have tenderness over this point.
• Cross arm adduction will illicit pain at the ACJ (a blunt test for problems with ACJ – maybe chronic or acute)
• Altered contour of the shoulder at the ACJ  compared to other side.

Diagnosis and classification is made clinically and radiographically

Normal and Grade I

Case courtesy of Dr Craig Hacking, Radiopaedia.org. From the case rID: 37930

There is a gap visible between the distal clavicle and acromium (5-8 mm – narrower in the elderly)

There maybe a small amount of widening of the joint space in Grade I

The inferior borders should align.

Grade II 

Case courtesy of Dr Henry Knipe, Radiopaedia.org. From the case rID: 30774

There is widening of the ACJ space

The inferior border of the clavicle is raised in respect to the acromium but not above its superior border.

Note the altered soft tissue line over the superior edge of the distal clavicle.

Grade III

Case courtesy of Dr Benoudina Samir, Radiopaedia.org. From the case rID: 49917

The inferior border of the clavicle is raised in respect to the acromium above its superior border.

Grade IV

Case courtesy of Dr Henry Knipe, Radiopaedia.org. From the case rID: 30774

The clavicle is displaced posterior into the trapezius.

Grade V

Case courtesy of Dr Bruno Di Muzio, Radiopaedia.org. From the case rID: 44768

The Clavicle is  markedly elevated with coracoclavicular distance more than twice normal.

Grade VI

Case courtesy of Dr Jeffrey Hocking, Radiopaedia.org. From the case rID: 48600

The clavicle is inferiorly displaced behind coracobrachialis and biceps tendons.

Comparative views can be useful if you are clinically suspicious of an ACJ injury, but normal AP views are not conclusive.

Treatment and Referral

Grade I-III

Manage in a sling

refer to Upper Limb Physio.

Grade I&II likely managed conservatively.

Grade III management varies dependant on specialist and patient.

Grade IV-V(rare)

Manage in a sling.

Consider referral to on call orthopaedics,

otherwise Upper Limb Physio.

Very likely to need surgery.

Grade VI (very rare)

Refer to on call orthopaedics.

Further reading

With thanks to

www.shoulderdoc.co.uk/article/60

www.orthobullets.com/shoulder-and-elbow/3047/acromio-clavicular-injuries-ac-separation

radiopaedia.org/articles/acromioclavicular-injury?lang=gb

radiopaedia.org/cases/rockwood-classification-of-acromioclavicular-joint-injury-annotated-radiographs-1?lang=us