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Let's start with some basic meniscal anatomy.

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This is the point of view of the femur looking down

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atop the tibia, showing you the medial meniscus on the left

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and the lateral meniscus on the right.

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And as you look at this, you can appreciate

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that they are not of similar size or shape.

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The medial meniscus is a more elongated structure.

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The lateral meniscus is a more circular structure.

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Indeed, the lateral meniscus covers more

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of the lateral tibial plateau than does the medial meniscus

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of the medial tibial plateau atop.

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This particular illustration is one

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of the ligaments we'll talk about later

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that connects one meniscus with the other.

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This is the anterior transverse meniscal meniscal ligaments.

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Now, this was a diagram we had made many years ago when I

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first learned about the root ligaments,

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which we'll be talking about later on in this lecture.

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The root ligaments are shown here,

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numbered 1, 2, 3, and four.

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Two of them on the medial side, two

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of them on the lateral side, one anterior,

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one posterior on either side.

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And as you look at them, you just get an idea that those

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root ligaments of the lateral meniscus, numbers three

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and four are much closer together than the root ligaments

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of the medial meniscus.

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With regard to meniscal function,

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I list here five particular factors.

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I'm not gonna talk about all of these,

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but I wanted to comment on shock absorption.

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Indeed, these meniscus serve to absorb some of the shock

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that extends across the knee joint.

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And I like this sagittal section

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because it shows you pictures

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of the posterior anterior horns of the meniscus.

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And as you look at the area of damage

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to the articular cartilage,

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it's much greater in the uncovered region,

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particularly on the femoral side, than on the covered region

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where the menisci are situated.

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So they, these menisci are important in shock absorption.

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Now, let's comment a bit about the meniscal blood supply.

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I learned early on that the meniscus

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of the knee had four blood supply,

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but that has a peripheral blood supply.

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And that peripheral blood supply is supplied

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by two particular sources,

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and I've labeled them in the image numbers

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one in number two.

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Number one are the branches of the ular vessels.

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They form a capillary plexus at the

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periphery of the meniscus.

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And number two is a synovial reflection,

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you can see at a top

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and at the bottom of the peripheral portion of the meniscus.

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So what this does is create a vascular segment at the

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periphery of the meniscus in a much wider avascular segment.

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Here are some figures giving you an

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Idea of how broad are the vascular segments in the medial

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and lateral meniscus.

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Now the orthopedic surgeons come along

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and they shorten the terminology to red and white zone.

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Here you can see in a specimen,

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the red zone not representing a lot of the width

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of the meniscus and the avascular white zone.

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Tears do well in the red zone,

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and in fact, often surgery is not required.

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Tears in the white zone do not do well.

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And indeed, meniscal resection

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that is partial menisectomy may be required.

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Here's a picture sent to me by David Rubin, showing you,

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in fact, a tear in the red zone, the peripheral zone

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of the meniscus.

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Now these may heal on their own,

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and when they do, they leave findings on the MR examination

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findings that can simulate new meniscal pathology.

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I show you that here with non-flu

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and fluid sensitive sequences

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and a magnified view to indicate

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what are the characteristics

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of a healed peripheral minuscule tear.

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Typically, the zone

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of abnormality is less than two millimeters.

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The signal intensity is intermediate as shown here,

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or sometimes bright, often not as bright as fluid.

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And there may be low signal intensity strands

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connecting the central

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and peripheral portions of the meniscus.

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So those are features that might help you,

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but this can be a diagnostic dilemma.