Acromial types

The shape of the acromion had been initially divided into three types (which was known as the Bigliani classification) 3, to which a fourth has been added 2. They are used as a standardized way of describing the acromion, as well as predicting to a degree the incidence of impingement. 


This classification was initially proposed by Bigliani et al. in 1986 on outlet view radiographs, and later modified by Kitay et al. 7 and Vanarthos et al. in 1995, which remains the most widely accepted classification at the time of writing (July 2016).

Acromion morphology (types) are based on sagittal oblique MRI:

  1. flat inferiorly (12%) 6
  2. curved (56%)
    • parallel to the humeral head with a concave undersurface 
    • considered most common type 3
  3. hooked (29%)
    • the most anterior portion of the acromion has a hooked shape
    • associated with increased incidence of shoulder impingement
  4. convex (upturned) (3%)
    • most recent classification of acromion process shape
    • the undersurface of the acromion is convex near the distal end 4
    • no convincing correlation between a type 4 acromion and impingement syndrome exists 4, 5

See also

Anatomy: Upper limb

Anatomy: Upper limb

Article information

rID: 842
Section: Anatomy
Synonyms or Alternate Spellings:
  • Acromion types
  • Types of the acromion
  • Bigliani classification of acromion types
  • Bigliani classification of acromion morphology
  • Bigliani classification

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Cases and figures

  • Figure 1: four types
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  •  Type 1
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  • Type 2
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  •  Type 3
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  •   Type 3
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  •  Type 3
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