The four types of acromion, classified based on their shape, are flat, curved, hooked, and convex (upturned). These classifications are relevant to understanding and diagnosing shoulder impingement syndrome.
Here's a breakdown of each type:
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Flat: The undersurface of the acromion is flat. This type is the least likely to be associated with shoulder impingement. It represents approximately 12% of acromions.
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Curved: The acromion is parallel to the humeral head and has a concave undersurface. This is the most common type, representing about 56% of acromions.
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Hooked: The most anterior portion of the acromion has a hooked shape. This type is more likely to contribute to rotator cuff impingement. Around 29% of acromions are classified as hooked.
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Convex (Upturned): This is the most recently described classification, where the acromion has an upward curvature. It is the least common, representing approximately 3% of acromions.
The shape of the acromion can influence the space available for the rotator cuff tendons. A hooked or convex acromion, for instance, may decrease this space and predispose individuals to rotator cuff impingement and related shoulder pain.
