Anterior Cruciate Ligament Anatomy: Axial View
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Knee anatomy.
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Cruciates anterior cruciate ligament, axial projection.
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We've got a diagram showing our anterior cruciate ligament,
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which has a smaller anteromedial bundle and a
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larger posterolateral bundle with flexion.
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The femoral attachment of the ACL
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assumes a more horizontal orientation.
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So if you overflex the knee more than ten degrees,
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the ACL is going to look like it's coursing in the wrong projection.
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You also want to perform the examination in about ten degrees
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of external rotation. If you overrotate one way or another,
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too much external or too much internal rotation,
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the ACL is going to look strange or weird in the sagittal projection.
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And you don't have to necessarily bring the patient back,
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go to the axial and coronal projections, just as we're doing now.
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Now, with the knee in flexion,
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the anteromedial bundle tightens and the posterolateral bundle
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loosens. So this may get a little bit confusing.
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Also, in flexion, the anteromedial bundle fibers twist
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or spiral over the posterolateral fibers.
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They become a little bit wavy and they're curving around each other.
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And this may also give the false impression of a tear.
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So here's our ACL arising from a fossa,
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just anterior to the anterior tibial spine.
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If it were present along the supracondylar notch,
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we might see a plica attachment
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which is called the ligamentum mucosum.
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And going forward and up, or superiorly or proximally, would be the
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infrapatellar plica. But that will be a story for another day.
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So we follow our anteromedial and posterolateral
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bundles on our diagram as they course back,
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especially when we are in a difficult position.
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We're tied in a Gordian knot from poor positioning by the
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technologist in the sagittal projection.
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We rely very heavily on this projection.
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And we watch the ACL paralleling with a straight,
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taut configuration, the inner edge of the lateral femoral condyle
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lying just deep to the oblique popliteal ligament.
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Let's keep going, shall we?
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Oh, it's nice and snug as a bug in a rug.
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Yes, there is a little lump or bump along the lateral
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aspect of the medial femoral condyle.
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And we see the footprint of attachment of the ACL at its second highest,
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and then finally, at its highest point.
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Not interrupted, but contiguous on every single slice.
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So the axial projection,
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my most favored nation projection for assessing the anterior
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cruciate ligament high up, especially the femoral end.
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I use the sagittal projection more for the mid to distal portion.
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I use the axial projection for the proximal femoral attachment over
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the top position portion. Don't forget to look at the other
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accompanying vignettes.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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