An os acromiale is a persistent accessory ossification centre of the lateral acromion.

  • It's normal to see the accessory ossification centre until around 15 years of age.
  • But there should be complete fuse by 25.
  • If there is non fusion and a persistent os after 25, it's termed an os acromiale.

It may be completely asymptomatic but there are two potential complications.

  1. Impingement on the Rotator Cuff tendons.
  2. Acromial apophysiolysis.

  • There can be abnormal movement between the acromion and the OS Acromiale.
  • This results in the OS moving inferiorly & impinging on the RCT.
  • Additionally, if there is malalignment between the OS and the Clavicle, this can lead to narrowing of the subacromial space.
  • For acromial apophysiolysis, we will look at this specifically in the next post.

  • So how do you best recognise an Os Acromiale on Shoulder MRI.


  • Its easy to miss if you don’t look for it specifically and the key is to look at the axial scans where it is most obvious.


  • You can see it on coronal images but it's much harder and sagittals are not much help.


  • See the video below which demonstrates how to find an os acromiale on MRI Shoulder.

If your Browser is blocking the video, Please view it on our YouTube Channel HERE.

Learn more about SHOULDER Imaging in our ONLINE 
Guided MRI SHOULDER Mini-Fellowship.

More by clicking on the images below.

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