LCL Complex on MRI
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Let's run the table on the LCL, or fibular collateral ligament
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in the axial projection and our depiction of the anatomy on MRI.
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There is the fibular collateral ligament.
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Let's get you oriented.
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Right next to it, by the way,
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is the popliteus tendon, which is going to go back, down, and distal, and more medial.
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But we're concerned with this structure right here.
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Sitting atop of it is the large muscular structure, the biceps femoris.
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So let's scroll down.
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When we scroll down, we run into the popliteus hiatus, which is right here.
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There's the popliteus hiatus.
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Above the popliteus hiatus is the FCL.
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So let's follow the FCL right to this location.
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There's the FCL.
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Follow it down.
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Mixes a little bit with the popliteus tendon,
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follow it up, and you can see that it hits the lateral aspect of the femur in a small
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osseous depression, slightly flattened, slightly depressed,
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approximately 1.4mm proximal and 3.1mm posterior to the lateral femoral condyle.
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It's immediately anterior to the attachment or origin of the lateral
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gastrocnemius head, which I'm not going to show you at this very moment.
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Now, the distal extension is directed in a posterior fashion.
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Let's see that. We start up high,
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let's go down low. It should go posterior.
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And it does.
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There it is.
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And it's going to meet up with the biceps femoris to insert on the lateral aspect
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of the fibular head, not the styloid, which is the site for arcuate and other
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insertions as described in other vignettes.
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This merging with the biceps femoris
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heads is actually not anatomically purely correct.
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But when you look at it on MRI, they do appear to merge.
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Thus the name, the conjoint tendon.
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There's a J-shaped bursa that's interposed between the LCL.
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Let's follow the LCL back.
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Here's our conjoint insertion.
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Let's go back up and separate them out.
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There's the LCL.
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There's the biceps femoris.
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There's the J-shaped bursa that is rarely filled.
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It's described in cadaveric studies,
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but you almost never see it filled with fluid on MRI.
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So these axial plane relationships are critical because it's going to help you
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evaluate the rest of the posterolateral corner of the knee, including the oblique
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popliteal ligament and some other critical structures like the arcuate.
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And that will be a story for a separate vignette
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in the posterolateral corner.
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The axial anatomy of the fibular collateral ligament,
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it's joining with the biceps femoris to form the conjoint inserting
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on the lateral aspect of the fibular head, not the fibular styloid tip.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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