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Knee anatomy.

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Cruciates anterior cruciate ligament part two.

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The anterior cruciate ligament, seen right here,

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is an intraarticular yet extra synovial structure.

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Even though it is surrounded by this blue aquamarine sheath right here.

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So that sheath is actually a reflection.

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The synovium is found around the outside.

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So do remember that the ACL is an extrasynovial structure.

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Still, this sheath can swell prominently and produce a pseudo mass

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that envelops not just the ACL but also the PCL,

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and as stated previously, pushes out the back.

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Now, the proximal ACL is attached to a fossa,

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which we'll see in the axial and coronal projection

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along the posteromedial aspect of the lateral femoral condyle.

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And that's where we are right here.

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And this critical over-the-top position will be defined in a moment.

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The ACL origin has a variable width on sagittal MRI

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because of volume averaging.

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So I don't want to take much time in discussing that portion of it.

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But at its midportion, it should be about 11-12 mm in diameter,

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a little bit narrower than the posterior cruciate ligament.

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Posteriorly, you're going to find it in the intercondylar notch.

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And one common mistake is not to look at the notch shape and size,

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which I'm going to encourage you to do

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as we look at pathologic cases distally.

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The ACL extends inferior medial to the anterior tibial intercondylar area,

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and we're going to see that better in the axial projection.

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But this pattern of fanning, once we get past the midportion of the ACL,

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spreads the ACL out and can make it look a little less conspicuous,

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especially if the sheath is swollen, the distal ACL may be obscured.

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Now, the distal attachment is to a fossa that is anterior

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and lateral to the anterior tibial spine.

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So the anterior tibial spine is a very important anatomic landmark.

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We don't see it here just yet, but we will.

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And it also got attachments between the anterior attachments

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of the menisci.

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So there's kind of a spreading-type attachment that's epicentered

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just anterior and lateral to the anterior tibial spine.

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Now, let's talk about this central origin right here.

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I'm going to draw a line.

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In fact, I'm going to make my line a little bit thicker just for giggles here.

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My black line.

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And I'm going to draw a line along the posterior femur.

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And I'm going to come straight down to this point.

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And then I'm going to put a dot along the posterior femoral condyle.

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Right?

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The condyle meets the femoral shaft right there.

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And I'm going to go 15 mm in, so we're going to say that's 15 mm.

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That spot is where the ACL actually penetrates the femur.

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And when you're doing a graft,

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that's where the graft needs to go, in that exact location.

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This is a critical landmark.

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The attachment of the ACL distally, not as critical to evaluate,

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especially in a graft scenario.

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On the average,

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going from the center of the PCL to the center of the ACL,

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the average is about 2 cm.

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But there's a fair amount of variability from person to person,

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especially depending upon how steep the femoral roof is,

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and that varies from person to person.

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This location right here that I've got marked with my black dot is called

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the over-the-top position for anterior cruciate ligament grafting.

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As stated, the ACL is a little thinner than the PCL, about 11-12 mm.

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Its length is somewhere between 31 and 38 mm.

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Remember, the PCL, about 38 mm.

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And once again, as stated,

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the distal attachment is going to be a lot broader

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than the pinched-appearing proximal attachment.

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And this fanning starts to occur about the middle

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or distal third of the ACL.

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The blood supply to the ACL is via midgenicular artery branches

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that form a plexus.

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The plexus can usually be seen down here, and I've got it drawn in.

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And although not drawn in here,

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because the patient didn't have a prominent one,

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there is a fibrous band that is present in some

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patients called the ligamentum mucosum.

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And that ligamentum mucosum often attaches to the more delicate

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in the retropatellar region.

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So that's a slightly more advanced view of the ACL diagrammatically.

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Don't forget to move on to some of the other accompanying vignettes.