Learning Radiology xray montage
Acromioclavicular Separation
AC Separation

  • Normal anatomy of acromioclavicular (AC) joint

    • Synovial joint
    • Acromioclavicular ligament
      • Weaker
    • Coracoclavicular ligaments
      • Medial conoid and lateral trapezoid
      • Denser, thicker, stronger

From Harris and Harris, Radiology of Emergency Medicine

  • Normal measurements

    • AC joint space is usually <5mm
      • Right and left differ by no more than 2-3 mm
    • Coracoclavicular distance usually <11-13 mm
      • Right and left should differ by < 5 mm
    • 50% difference in size between the two shoulders is considered significant
    • Inferior plane of the distal clavicle should be on same plane as inferior border of acromion
      • Developmental variations reported as high as 19%
  • Fall on shoulder is frequent mechanism of injury
    • Point tenderness, limitation of motion
  • Abnormal widening of the AC joint due to disruption of the AC ligament
    • CC separation is the more important soft tissue injury
  • Extent of CC separation has direct effect on degree of AC separation

  • Classification



Radiographic findings




Stretching of AC ligament

AC joint is stable

CC ligament intact

Only seen on stress views of injured and uninjured shoulders=widening of AC joint

No instability



Partial or complete rupture of AC ligament

Partial, but not complete, disruption of CC ligament

Widening of AC joint but a normal coracoclavicular distance

Stress films may still be required to demonstrate widening of both AC joint and CC space


May require arthroplasty


Disruption of both AC and CC ligaments

Widening of both the AC and CC spaces on routine erect film

Internal fixation


AC and CC ligaments disrupted but coracoacromial ligament remains intact

Distal end of clavicle lies inferior and posterior to acromion seen best on axillary view




AC and CC ligaments disrupted
Coracoacromial ligament remains intact Sternoclavicular separation occurs as well

Marked widening of both the AC and CC space

Sternoclavicular dislocation



Distal end of clavicle displaced inferiorly and lodges in biceps and coracobrachialis muscles

Distal end of clavicle comes to lie inferior to acromion


Two views of right shoulder show elevation of the clavicle
and separation of the AC joint in a Type III AC joint separation

  • Fracture of distal end of clavicle is frequently associated with CC tears with or without separation of AC ligament
  • Separation may heal with soft tissue calcification or ossification 


Harris, J and Harris, W: Radiology of Emergency Medicine, 4th ed, 2000.

Manaster, B., Disler, D.,May, D.: The Requisites: Musculoskeletal  Imaging, 2002