Case 2

AC Joint Separation (ABCS Approach):​

A – Alignment

• Compare with contralateral shoulder.

• Disrupted alignment between distal clavicle and acromion.

• Clavicle often appears elevated relative to acromion (“step-off”).

Case courtesy of Maulik S Patel, Radiopaedia.org, rID: 12560

B – Bones

• Rule out distal clavicle fracture or associated coracoid fracture.

• Check scapula and humeral head for additional injury.

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C – Cartilage/Joint spaces

• AC joint space is widened (>7 mm).

• Coracoclavicular (CC) distance may also be widened (>13 mm or >5 mm difference vs other side).

• Severity is graded (Rockwood classification I–VI).

Case courtesy of Andrew Murphy, Radiopaedia.org, rID: 72436

S – Soft tissues

• Localized soft tissue swelling over AC joint.

• Possible disruption of AC or CC ligaments (not directly visible but inferred by widening).
   

Pearl: A “weighted view” (patient holding weights) can accentuate the separation if diagnosis is uncertain.