How to Read an MRI of an ACL Tear

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In this video, Colorado knee surgeon Dr. LaPrade identifies how to read an MRI of an ACL tear. He looks at the normal anatomy of the knee and what a torn ACL looks like and the secondary signs of an anterior cruciate ligament injury.

Starting with a sagittal view of the lateral aspect of the knee, we move more medial the first thing we see is bone bruising. Bone bruising is usually present with an ACL tear on the anterior aspect of the lateral femoral condyle and the posterior aspect of the lateral tibial plateau. About 70% of people with an ACL injury have a bone bruise. This bruising is usually due to the subluxation that happens with an ACL injury.

Normally, the ACL is a dark structure in the center of the knee. In this case, the ACL is completely blown apart. There is some evidence of the ACL fibers, but we just do not see the normal ACL.

As we move more medial we start to see fluid in the joint, which is consistent with bleeding from an ACL tear. It is also common for there to be a tear to the posterior horn of the medial meniscus with an ACL injury.

We then move to the coronal images. As we start to move more posterior we look for bone bruising and we start to see a stump of a torn ACL. Instead of seeing normal contour of the dark ACL substance, we start to see more a balled-up appearance. In this view we can also see the injury to the posterior horn of the medial meniscus.

Finally, we look at the axial views, although these are not as useful when looking at ACL tears. You can see the fluid present within the joint.