The Basics of the Posterior Cruciate Ligament
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Knee anatomy.
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The cruciates, the PCL.
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A PCL is a central knee stabilizer for articulating bones.
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It resist varus-valgus but especially keeps the tibia
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from migrating posteriorly. So when the PCL is torn,
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the tibia is going to sag posteriorly and you might even end up
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lying on your back with something called the tibial sag sign.
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It also resists external rotation of the tibia,
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and we'll talk more about that in a moment.
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It is an arc-shaped kind of fatty structure compared to the ACL.
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It's a little bit thicker, about 13 mm in width,
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where the ACL about 11-12 mm.
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And it has behind it a round structure that you're seeing coursing in and
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out of the plane called the meniscofemoral ligament of wrisberg,
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which helps stabilize the lateral meniscus and arises
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from it coursing across the back of the knee.
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I have it drawn here in pink.
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And then more parallel is this arc-shaped structure
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that is kind of like a mini-me of the PCL called
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the meniscofemoral ligament of Humphrey.
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Now, the footprint of the PCL
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and the Humphrey ligament is quite complex.
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Sometimes these 2 may come together,
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sometimes they're very discrete and separated.
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And as a result of this, a pitfall may occur anteriorly
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that I'll share with you a little bit later on.
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Now, the PCL fibers are twisted so they're arc.
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They arc around or torse around each other,
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unlike a more parallel configuration to the ACL.
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And this has an effect on how it tears.
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For usually when the PCL tears it does not fully retract or separate
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like the ACL does. It kind of fills with blood and fluid.
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Another important take home message is the PCL inserts in a depression
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on the back of the tibia that lies below the tibial plateau.
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So if a surgeon is looking from the front, especially with the ACL intact,
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it is very hard to see and even get to this portion of the PCL.
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So tears here are the domain of MRI, unless there's a fracture,
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in which case you can see the evulsion fracture on a plane film.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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