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Knee anatomy on MRI.

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Let's focus on the medial collateral ligament,

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which Warren and Marshall divided into three layers

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from superficial to deep.

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Although, we're going to break them down into layers one,

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two and three.

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I'm going to focus on layer number one in this vignette,

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with a little contribution from layer number two, and try to avoid

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the terms superficial, middle, and deep where I can.

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Now, the reason for that is layer number one consists

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of deep fascia. So it's a little confusing.

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If this is the most superficial layer,

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what's it doing with a deep fascia-labeled structure?

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So that's why we'll stay with this nomenclature.

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So layer one consists of deep fascia with some

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fibers of the medial retinacular monetarily.

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It also forms the anterior fascia of the sartorius and a very

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thin membranous fascia layer less than a millimeter in

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thickness posteriorly.

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Here is layer number one.

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It's thin.

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There is often a little bit of fat underneath it.

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If it's injured, sometimes you'll see a little bit of swelling here.

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This layer is sometimes referred to as the "Crus layer."

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Thus it's labeled with the letter C.

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Pay no attention to layers two and three for now.

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In the axial projection, anteriorly, layer number one,

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the Crus layer,

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which may have a little bit of fat underneath it,

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a fat pad between it and layer number two, anteriorly,

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receives some contribution and support from the medial

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parapatellar retinaculum and from the medial

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patellofemoral ligament, or MPFL,

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which is the anterior continuation of layer number two.

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Layer number two is also known as the

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superficial portion of the MCL.

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But we'll leave that for a few moments

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later, so as not to confuse you.

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Let's focus only on layer number one

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and have a look on an MRI right now.

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On MRI and the axial projection, we have a thin,

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wispy structure.

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Perhaps it's easier to follow it from just in front of the

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sartorius as it arcs forward as a very thin structure that's

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very superficially located and has underneath it,

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portions of the medial retinaculum.

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And these two will actually come together, as they are right here,

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and then they will come together with another structure

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underneath it, the medial patellofemoral ligament

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which is part of layer number two.

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So here is layer number one, and also another component

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of layer number one, the deep fascia.

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So the deep fascia is fusing with the medial peripatellar

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retinaculum to form layer number one.

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Layer number one will fuse with layer number two, the MPFL.

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And those two will converge on the superficial MCL,

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which is layer number two,

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which many of you have called for many years,

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the tibial collateral ligament.

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Let's look at this in the coronal projection.

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Where is our superficial Crus layer or, we said we weren't

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going to use the term superficial, layer number one.

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Well, there it is right there.

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There's layer number one.

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And what's underneath layer number one?

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Layer number two.

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In the mid-coronal plane,

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layer number two is known as the superficial portion

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of the MCL, the middle layer.

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Middle layer.

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Layer number two.

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Superficial layer.

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Layer number one.

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Composed of deep fascia and medial retinaculum.