Case 14 Answer:

Here is another case of the same thing. Actually this is a much more common appearance than the huge fracture fragment on the previous exam.

Answer: Segond fracture.

What is it: avulsion fracture of the lateral aspect of the lateral tibial plateau (and yes, there is contention of what is actually avulsed. Most believe it to be the mid portion of the lateral capsular ligaments).

Why is it important: because it is often related to internal knee ligamentous injury, particularly the ACL

Reference: http://radiopaedia.org/articles/segond-fracture

Interestingly, there may be also be a more horizontal bony fragment hiding behind the tibial plateau that could be an additional arcuate sign of a fibular head avulsive fracture. http://radiopaedia.org/articles/arcuate-sign Certainly difficult to tell age on this single image.