Acromial types

Dr Jeremy Jones and A.Prof Frank Gaillard et al.

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

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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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