0:00

So I know we like to focus on MRI, this is an MRI course,

0:04

but it's also important to understand

0:07

the radiographic evaluation

0:08

of anterior cruciate ligament reconstructions.

0:10

We have to remember that radiographs as well

0:14

as MRI are static exams.

0:15

They don't tell us what's going on dynamically

0:17

with the joint, but can give us some clues.

0:21

So we wanna look at the femoral tenal fal

0:24

and tibial tunnel placement, assess for any,

0:27

any tunnel widening and also look for hardware loosening

0:30

or mal alignment.

0:33

So it's where as the femoral tunnel, uh, is concerned.

0:36

Uh, we wanna use bloomin SATs line as our anatomic landmark,

0:40

and ideally the femoral tunnel should be placed

0:43

as far posteriorly

0:44

as possible without violating the posterior wall

0:47

of the medial, uh, excuse me, the lateral femoral condyle.

0:51

So the sweet spot is at least 60%

0:54

or more posteriorly along that bloomin SATs line.

0:59

And the femoral tunnel by far is the most important in terms

1:03

of tunnel placement more so than the tibial tunnel.

1:07

So here's just an example

1:08

of an adequately placed femoral tunnel

1:10

on a lateral knee radiograph.

1:11

You can see this patient at dispensary fixation

1:14

with a cortical button,

1:15

and we can see the center of

1:17

that footprint is right at the back wall of the lateral

1:21

of the intercondylar notch along the

1:23

lateral femoral condyle.

1:26

So why is femoral tunnel, um, placement important?

1:29

Well, this, um, introduces the idea of isometry.

1:32

That means that that ligament has a constant length

1:36

and tension to route the range of motion of the knee.

1:38

And this is something they'll do intraoperatively, uh,

1:42

as they're placing the graft

1:43

and when they place, uh, when they're finally,

1:46

uh, closing up as well.

1:48

So when the knee is ranged from flexion to extension,

1:51

this ACL graft more

1:53

or less, has a constant length in

1:55

tension throughout that range.

1:57

If the graft is placed too far anterior in

1:59

that femoral tunnel, you can imagine

2:01

that the graft becomes lax in knee extension.

2:05

And conversely, when the, um,

2:07

graft is placed too far posterior, sometimes referred to

2:10

as an over the top position, it can result in stretching

2:13

and graft failure over time.

2:16

So here's an example of a graft that was placed

2:19

a little bit on the low side in terms of its, uh,

2:22

relationship to the roof of theon or notch.

2:25

And you can see here that this ACL has more

2:28

of a horizontal lie.

2:30

Normally, again, native ACL

2:32

or reconstructed ACL should be, uh, roughly parallel

2:35

or slightly steeper.

2:36

Tolu beta's line. This patient had a significant

2:39

laxity on exam.

2:42

Here's another example of a too far anterior position

2:45

of the tibial, uh, of the femoral tunnel, excuse me.

2:48

And you can see that this tunnel should be back here,

2:51

but instead placed too far anterior.

2:54

And this patient had, uh, pain and recurrent instability

2:59

And I think Dr.

3:00

Resnick reviewed this, um, yesterday.

3:02

Uh, talking about, uh, the footprint

3:05

of the anterior cruciate ligament.

3:07

There's a ridge at the posterior aspect

3:09

of the anterior cruciate ligament footprint,

3:12

which arthroscopists are known, uh,

3:14

to evaluate and look for.

3:16

And that marks the posterior aspect of the femoral condyle.

3:20

But in front of that footprint is another ridge,

3:23

often referred to as the resident's ridge.

3:25

Uh, because as residents, uh, are learning arthroscopy,

3:29

they may, may mistake this resonant ridge

3:31

or lateral intercondylar ridge as the back wall of the femur

3:35

and placed the anterior cruciate ligament graft in front.

3:38

So that may have been what happened, uh, in this situation.

3:44

Here's what it looks like on arthroscopy.

3:46

I know this image doesn't show a whole lot,

3:48

but supposedly this is the lateral intercondylar ridge

3:51

and here's the native of bare footprint

3:53

of the anterior cruciate ligament.

3:55

So you don't want to put your graft in front of that.