The Posteromedial Corner: Posterior Oblique Ligament part 2
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Knee anatomy on MRI, the posterior oblique ligament,
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also known as the ligament of Winslow.
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Winslow's got his name on a lot of stuff.
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It takes its origin right in front of the adductor tubercle.
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So the tubercle would be about here.
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There's the origin of the POL.
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So most people describe the origin to be at
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or near, or just anterior to this structure.
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Then we've got three separate components: a capsular
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or superior arm, a central tibial arm,
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and a distal superficial arm.
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So let's talk about the arms.
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First, the central or tibial arm.
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Now, that one's a little bit smaller,
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but it's actually the most important.
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So it may be the hardest to see or maybe hard to see,
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not as easily seen as this fatter distal superficial arm,
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but it extends posteriorly and obliquely.
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Thus the name posterior oblique ligament of the knee.
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It attaches to the posteromedial aspect of the medial
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meniscus and the adjacent component of the tibia.
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So we'll see on MRI that there's a component to the
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posteromedial meniscus that's most important and critical
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in the posteriorsuperior quadrant of the meniscus corner.
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Now, the distal end of the POL passes deep to the anterior
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arm, or reflected arm of the semimembranosus.
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So here's the reflected arm of the
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semimembranosus right there,
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and underneath it is the central tibial arm of the POL
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coursing right underneath it, the superior arm,
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also known as the capsular arm.
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It is superior to the joint line.
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It is a somewhat horizontal course.
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It's continuous with the posterior joint capsule.
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It fuses with the capsular arm of the semimembranosus,
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and it contributes to the back capsule of the
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knee and the oblique popliteal ligament,
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which are virtually indistinguishable
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from one another on MRI.
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Then we've got the distal superficial arm.
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It attaches to the sheath and tibial insertion
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point of the semimembranosus.
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It blends with the posterior margin of the superficial MCL.
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So this one is the easiest to see,
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even though it's not the most important.
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This one is. You may see a little cleft between the two,
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but on sagittal MRI,
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you'll actually see a different course of the fibers.
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These will be more straight up and down,
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and the distal superficial arm will have an obliquity
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this way from proximal anterior to posterior
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and inferior. And then it'll come back in,
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making somewhat of a triangle.
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Again, you'll appreciate this better on a real MRI image.
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And this particular component passes superficial
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to the pars reflexa of the semimembranosus.
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So the anterior arm is located between the central
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arm and the distal or superficial arm of the POL,
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namely the pars reflexa bisects the
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two and goes in between them.
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
ProScan Imaging
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