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Knee anatomy posteromedial corner.

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We've talked about the POL, the OPL and some of the other structures.

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It's time for the posteromedial capsule and the posterior horn of the medial meniscus.

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Now, let's take a look at our sagittal, or lateral diagram.

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Here's the posture oblique ligament of the knee.

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The most important component is the central tibial arm, which courses

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obliquely backwards to insert on the tibial and the inferior capsule.

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We also have a superior capsular arm

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that sweeps back and contributes to the capsule, to the upper capsule.

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So the capsule is reinforced by components of the POL.

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And so it's considered a major supporting structure of the posteromedial corner.

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Now, the medial meniscus is linked

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to the semimembranosus through a neurophysiologic pathway.

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So if you stimulate the posterior horn of the medial meniscus, this actually

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results in a somatosensory evoked potential in the semimembranosus muscle,

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and you can actually see a little

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fibrillation sometimes of the POL pathophysiologically.

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Now, let's talk a little bit about biomechanics and the capsule for a minute.

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When the knee is extended,

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the tibia rotates, kind of like you would rotate a screw into a piece of wood.

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And this is known as the screw home mechanism.

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The popliteus has an analogous function on the lateral side.

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So it helps to tighten the capsule

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and the POL help to tighten

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the posteromedial corner and certain positions, namely in full extension.

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Now, I'd like to move to a slightly different diagram.

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Let's look at this oblique diagram

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for a minute and focus on the position of the POL relative to the meniscus.

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And remember, we are oblique. So here,

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it looks more posterior than it really is.

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It's kind of in the posterior mid-coronal portion.

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But the reason I show this is, look at its very, very tight proximity to this aquamarine

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blue structure, which is the posteromedial meniscus.

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Now, the posteromedial capsule, when the knee is flexed, gives active

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support to the meniscus along with the pes anserinus muscles,

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the semitendinosus gracilis and sartorius and their tendons.

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When the knee is extended, there is active support to dysfunction via

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an unexpected structure namely the vastus medialis.

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Now, let's take a look at another diagram for a minute before we get into MRIs.

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And the posterior medial meniscus, we said, is supported by a number of structures,

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particularly the capsule and the POL or posterior oblique ligament of the knee.

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And there is a meniscocapsular junction

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and there are meniscocapsular attachments which are not drawn in. Although we do see

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one of them right here adjacent to the semimembranosus.

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So the stabilization of the meniscus as you flex and extend, kind of like rotating

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a tire, keeps the meniscus in a stable position as long as these attachments,

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this one being a capsular attachment to a semimembranosus reflection, is intact.

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If you lose those capsular stability

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attachments, then as you rotate the tire, what does the meniscus do?

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It squidges out.

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It squishes out.

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And when that happens, it destabilizes the knee and puts other structures at risk.

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In other words,

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it causes stress on the other structures and increases the risk of injury to other

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surfaces, especially the tibial articular surface.

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This stability is known as the brake stop mechanism.

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And if you lose the capsule on the back or

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lose these capsular attachments, then you will lose this brake stop mechanism.

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And now you set yourself up for additional

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injuries to the cartilage surface, to the tibia, and to other structures.