The Posteromedial Corner Anatomy on MRI
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Knee anatomy on MRI.
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Here is an MRI, sagittal or lateral, T1 fat weighted.
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In the middle, sagittal or lateral, water weighted.
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And on the right, coronal AP type projection, also water weighted.
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We're focused on the corner, the posteromedial corner, which has five
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main structures. The posterior oblique ligament, which is discussed on its own
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but we can see a component of it, the capsular component,
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right here along the posterosuperior aspect of the medial meniscus.
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We can scroll it a little bit and we see
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it right there, and perhaps right there, as a linear pointed structure.
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Then we've got the OPL,
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which we can't really separate from the posterior capsule.
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But there it is, right there.
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So the capsule and the OPL are seen as one, not as two distinct structures.
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And the OPL is the oblique popliteal ligament.
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Now, we've got the semimembranosus.
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The semimembranosus, a dynamic stabilizer
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and an anterior reflected portion of it is called the pars reflexa.
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Then the semimembranosus continues
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on down as the direct component of the semimembranosus.
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There are actually five components,
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a capsular, an inferior, a dista,l and then the two major ones, which I've just shown
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you, the anterior pars reflexa and the distal... Sorry, and the direct...
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and the direct component.
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You can also see the direct component of the semimembranosus in the coronal.
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It's this big, fat, dark blob.
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It almost appears to wrap around the tubercle of the tibia.
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Now, another structure that is seen
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in this projection is the POL or posterior oblique ligament of the knee.
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How do we find that?
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Find your middle layer of MCL, also known as the deep portion
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of the superficial MCL, layer number two or middle layer.
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And then follow that posterior,
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and that will turn into, it will become the POL.
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So you're in POL right now.
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You see the posterosuperior aspect of the meniscus and the POL, fused.
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I'll make it a little lighter for you.
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Then the POL is going to wrap around behind that meniscus and it's going to be
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continuous with the posterior capsule and the OPL, the oblique popliteal ligament.
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So you've seen several structures of the posteromedial corner.
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You've seen the POL, you've seen the semimembranosus and two
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components, the anterior pars reflexa and the continuation of the direct head.
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Two other very important components are
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the posteromedial meniscus itself and its capsular attachment, which is seen here as
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these fuzzy areas of gray signal intensity on PD spur and on the T1 fat image.
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Let's move on to another vignette, shall we?
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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