Acromio-clavicular separation

Reference 

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

•  
• 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
   

Type	Anatomy	Radiographic findings	Prognosis
I Sprain	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
II Subluxation	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
III	Disruption of both AC and CC ligaments	Widening of both the AC and CC spaces on routine erect film	Internal fixation
IV Posterior	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
V Inferior	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
VI	Distal end of clavicle displaced inferiorly and lodges in biceps and coracobrachialis muscles	Distal end of clavicle comes to lie inferior to acromion