Subacromial impingement

Subacromial impingement is by far the most common form of shoulder impingement and occurs secondary to attrition between the coracoacromial arch and the supraspinatus tendon or subacromial bursa.

Primarily, subacromial impingement is a clinical diagnosis and one should not make a diagnosis or exclude it solely based on imaging; however imaging has an important role in supporting the diagnosis, finding the possible cause as well as sequelae of impingement. 

  • static imaging modalities such as MRI and radiographs occasionally depict reduced subacromial distance as an indirect evidence: 
    • type III acromion
    • os acromiale
    • osteophytes extruding from AC joint inferiorly
    • subacromial/subdeltoid bursitis
    • lateral acromial tilt
    • anecdotal experience also suggests that slight contact between the coracoacromial arch and the subacromial bursa can occur in healthy individuals; yet, significant contact or snapping between these two structures are not common in the absence of symptoms and suggest clinically relevant impingement 5 
  • dynamic ultrasound 
    • may depict abnormal contact between the coracoacromial arch and peritendinous tissue during shoulder abduction; however, dynamic diagnosis at ultrasound is not free of controversy: although earlier studies have demonstrated thickening of the subacromial bursa following shoulder abduction in symptomatic shoulders,1-3 a more recent investigation found no significant difference in the degree of bursal gathering in impingement patients compared with healthy volunteers 4

Less common types of shoulder impingement include:

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Article information

rID: 2042
Section: Gamuts
Synonyms or Alternate Spellings:
  • Sub-acromial impingement syndrome
  • Subacromial impingement syndrome

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Cases and figures

  • Scapular Y view
    Case 1: coracoacromial ligament ossification
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  • Supraspinatus tear
    Case 2: impingement from supraspinatus tear
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  • Case 3: type III acromion causing impingement
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  • Case 4
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  • Case 5
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