Causes and Diagnosis of Grade 3 Acromioclavicular Joint Separation

Mechanism of Injury and Risk Factors

The American College of Radiology suggests that direct trauma to the shoulder, typically from a fall directly onto the point of the shoulder with the arm in an adducted position, is a primary cause of grade 3 AC joint separation 1
Previous history of shoulder or clavicle injuries may predispose to AC joint separation, as noted by the Praxis Medical Insights guideline 2

The American College of Radiology recommends radiography as the preferred initial imaging modality for suspected AC joint separation, with upright positioning essential during radiography as malalignment can be underrepresented on supine imaging 1
The American College of Radiology also suggests that CT may be considered for complex cases but is not typically necessary for initial diagnosis of grade 3 AC separations, and MRI is generally not indicated for isolated AC joint injuries unless concomitant soft tissue injuries are suspected 1, 3