What finding is most characteristic of acromioclavicular (AC) joint separation?

What finding is most characteristic of acromioclavicular (AC) joint separation?

• A. Piano-key deformity with distal clavicle elevation
• B. Glenoid rim fracture
• C. Subluxation of acromion
• D. Posterior dislocation of humeral head

Answer: (A)

Acromioclavicular joint separation classically causes rupture of the AC ligaments and often the coracoclavicular ligaments, which lets the distal clavicle rise relative to the acromion. The hallmark sign is a piano-key deformity: when you press on the elevated distal clavicle, it can be depressed and returns like a piano key under pressure. This shows the clavicle is unstable at the AC joint. Radiographs often show widening of the distance between the acromion and clavicle, reflecting CC ligament disruption. The other findings point to different injuries: a glenoid rim fracture involves the shoulder socket itself, not the AC joint; subluxation of the acromion isn’t a standard descriptor for AC injuries; and posterior dislocation of the humeral head is a glenohumeral (shoulder) joint injury, not an AC separation.

Acromioclavicular joint separation classically causes rupture of the AC ligaments and often the coracoclavicular ligaments, which lets the distal clavicle rise relative to the acromion. The hallmark sign is a piano-key deformity: when you press on the elevated distal clavicle, it can be depressed and returns like a piano key under pressure. This shows the clavicle is unstable at the AC joint.

Radiographs often show widening of the distance between the acromion and clavicle, reflecting CC ligament disruption.

The other findings point to different injuries: a glenoid rim fracture involves the shoulder socket itself, not the AC joint; subluxation of the acromion isn’t a standard descriptor for AC injuries; and posterior dislocation of the humeral head is a glenohumeral (shoulder) joint injury, not an AC separation.