WHAT ARE THE FINDINGS?

• The ACL is enlarged and hyperintense but there is continuity of fibres and normal alignment.
  
  

• The enlargement is more prominent proximally giving it the appearance of a celery stalk (celery stalk sign of ACL mucoid degeneration).

SUMMARY:

This is a characteristic appearance of ACL mucoid degeneration. Look for, 

• Expanded hyperintense ACL.
   
• Fibres are continuous.
   
• Alignment of fibres is normal.

• Intra ligamentous cysts are commonly found in mucoid degeneration of the ACL.

• Size can be variable from small cysts like in this image to larger ones we will see next.

• Look for T2 hyperintense cystic changes in the ACL.

• Cysts can extend from the ACL into the bony attachments at the tibia or femur.

• Look for cystic change of variable size at the femor and tibia at the attachment site.

• Intraligamentous cysts can also extend into the adjacent soft tissue.

• It's not just the ACL that undergoes mucoid degeneration.

• The PCL can also be involved but it's less common.

• Mucoid degeneration of the PCL can be in conjunction with the ACL or on its own.

• Look for the same findings discussed for the ACL to make the diagnosis.

• Ligament thickening.
  
  

• "Celery stalk" sign.
  
  

• Increased T2 Signal intensity.
  
  

• Preserved fibres which are in continuity.
  
  

• Normal alignment of the ACL or PCL.
  
  

• Intra ligamentous cysts of variable size.
  
  

• Intra osseous extension of the cysts.