An avulsion is a tearing away of the normal attachment of an anatomical structure. 

Avulsions may occur where muscles are attached to bone, where the tendinous muscle attachment tears off the bone, often taking with it a small bony fragment.

Another kind of avulsion can occur with the knee meniscus, where the outer rim can be torn off the tibia bone, where it may normally have been attached with a ligament.

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An explanation of what it means to have a 'floating' knee meniscus on MRI imaging.

An overview of acute muscle and tendon injury around the knee.

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