Os acetabuli

Last revised by Yuranga Weerakkody on 26 Jan 2022

Os acetabuli (plural: ossa acetabuli) are small ossicles adjacent to the acetabular roof regions and may represent an unfused secondary ossification center of the acetabulum or pathological sequelae (e.g. acetabular rim fracture, femoroacetabular impingement).

Ossa acetabuli are located at the anterosuperior margin. They are rounded in shape with a concave lateral border and convex medial border. They may be bilateral and partially fused to the acetabulum.

Ossa acetabuli are normally seen in children but typically fuse in mid-to-late teens, being uncommonly seen in adults.

Ossicles in the acetabular region may also be found in: 

Some consider those present in dysplastic hips to represent fatigue fractures of the acetabular rim due to overload 4

In some situations consider:

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Cases and figures

  • Case 1
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  • Case 2: with pistol grip deformity (arrow)
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  • Case 3: bilateral os acetabuli with left pistol grip deformity
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  • Case 4
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  • Case 5: with femoroacetabular impingement - cam-type
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  • Case 6
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