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Acromioclavicular 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
     

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

 



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