0:00

So with that, we now will look at five scenarios

0:05

that can leave footprints behind related to internal force.

0:09

The first of these we'll cover quickly,

0:12

we've already talked about it.

0:13

It is distraction impaction, particularly the valgus injury.

0:18

What occurs here is impaction of the viral femoral condyle

0:23

and lateral aspect of the tibial plateau with widening

0:27

of the medial aspect of the joint.

0:29

So here we expect footprints

0:32

that will be contiguous at the time of injury

0:36

and generally contiguous at the time of imaging.

0:40

Let me show you this old case.

0:42

I include it because I knew exactly

0:44

where the external force was right there.

0:48

You can see some subtle edema here deep

0:51

to the LEL tibial tract impaction here with footprints left

0:56

behind contiguous on our imaging study.

1:00

This one looks like a contusion.

1:02

This one looks like an osteochondral fracture

1:05

with tensile injury to the medial supporting structure.

1:10

The second scenario is rotation.

1:13

I'm gonna rotate the tibia with respect to the femur,

1:17

but of course it could be the opposite here.

1:20

What occurs during the injury, contiguous

1:24

footprints left behind,

1:25

but when we image them, that particular uh,

1:29

joint is no longer rotator, at least not rotated

1:33

to the same extent.

1:35

So in these cases we see non-continuous

1:38

contusions or fractures.

1:41

Now these are common following anterior cruciate ligament

1:44

tears and I'll talk about, uh, my next lecture,

1:47

more common in the lateral side than on the medial side

1:51

and typically appear in the mid portion of

1:54

that lateral femoral condyle.

1:56

Here is a long abnormal notch

1:58

and the posterior aspect of the lateral tibial plateau

2:02

with a tear of the anterior cruciate

2:04

and in fact meniscal tearing as well.

2:08

Now this is often called a pivot shift injury,

2:12

which it is not.

2:14

A pivot shift is an abnormal response

2:18

to stress testing of the knee.

2:21

Yes, it is often seen in knees that have these footprints,

2:24

but there is no pivot shift injury.

2:28

The classic mechanism that does this

2:30

as anterolateral rotary in stability complicating uh,

2:35

complicating the analysis of

2:38

rotational injury is something called a coup

2:42

contracoup pattern of bone.

2:43

I, uh, injury when we have abnormal

2:47

rotation in one direction.

2:49

Here is internal rotation of the tibia

2:53

with typical footprints left behind.

2:56

We may have a overcorrection in the opposite

3:00

direction, external rotation of the tibia,

3:04

leaving footprints behind on the medial side as well.

3:09

You'll note on both sides there is in fact an offset between

3:13

where the femoral problem is

3:16

and where the tibial problem is generally further apart on

3:20

the lateral side than on the medial side.

3:25

The third mechanism is flexion.

3:27

I'm gonna flex the femur with respect to the tibia,

3:30

but it could be the opposite.

3:32

What occurs here is injuries, footprints

3:37

that are contiguous at the time of injury,

3:39

but when we image these patients,

3:41

typically the knee is no longer flexed.

3:45

So on imaging we see non-contiguous regions of bone injury.

3:49

Here's the point of contact at the time of injury.

3:53

Here's what happens when we are extending the knee.

3:57

And so the classic footprints here, bone contusions

4:01

involve the posterior aspect of the femoral condyle

4:04

and the posterior aspect of the tibial plateau.

4:08

When we see injuries, footprints of non-contiguous portions

4:13

of the femur and tibia,

4:15

typically we're dealing with rotation.

4:18

Okay, internal or external flexion.

4:21

And in many of these cases there are multiple ligamentous

4:24

and meniscal injuries with two classic patterns

4:28

that I would like to mention.

4:30

Flexion var, perhaps valgus as well.

4:33

And internal rotation of the tibia known as aery,

4:38

anterolateral rotary instability, the cause of agon fracture

4:43

with injuries to the ACL and lateral ligaments.

4:47

And the second mechanism, flexion valgus

4:50

and external rotation of the tibia known as amri,

4:55

an medial rotary instability.

4:58

One example is oue triad with injuries to the ACL

5:02

and to the medial ligaments.

5:05

Let me show you an example.

5:06

This is re taken from the internet, the picture,

5:11

but this are the images of a star, a halfback

5:14

for his high school football team.

5:16

He cut around a would be tackler, avoided him, heard a pop,

5:20

which is characteristic of tears of the ACL.

5:24

And here we can see Ry working with a sagon

5:29

fracture associated with a tear

5:32

of the anterior cruciate ligament.

5:35

You'll note here, internal rotation of the tibia

5:39

with respect to the femur.

5:42

The opposite, it would be amory.

5:45

This is an A picture, an exaggerated picture.

5:48

You'll see it once more in my lectures.

5:51

Okay, the history, this is a person playing badminton.

5:54

The athlete twisted his knee awkwardly

5:57

As he was reaching for a return note.

6:01

External rotation flexion.

6:03

Alright, this is what you see with uh, ous triad.

6:07

In this case, we're seeing

6:09

abnormality involving the medial supporting structure

6:13

as well as tearing of the anterior cruciate ligament amery.

6:18

The fourth basic mechanism that we will uh, deal

6:22

with is hyperextension.

6:24

In most of these cases, there is an external blow applied

6:28

to the anterior aspect of the knee.

6:30

So let's go ahead and put that in there with a

6:33

footprint left behind right here, then the knee is thrown

6:38

into hyperextension.

6:40

So I'll move this diagram into hyperextension

6:44

and what we see here are injuries dominating, footprints,

6:48

dominating, and the anor aspect of the femur and tibia.

6:53

They may be bone contusions, they may be fractures.

6:57

This sort of mechanism, as you know,

6:59

can result in cruciate ligament tears,

7:02

be they anterior cruciate, posterior cruciate,

7:06

or both as in this particular example.

7:11

The fifth and final type

7:13

of movement will be pure anterior translation.

7:17

And when we see this similar phenomenon

7:21

of non-contiguous regions of bone injury,

7:25

sometimes involving one side, sometimes involving both sides

7:29

of the knee, so simulating rotation as well.

7:35

So when we deal with the footprints that are left behind,

7:39

we try to find them be they contusions or fractures,

7:44

and based on their location, we can come up

7:47

with a possible mechanism of injury.

7:50

And knowing then the primary restraints

7:52

and secondary restraints to that particular movement

7:56

of the knee, we can decide

7:58

what ligaments are likely injured.

8:01

Valgus injuries, impaction, contiguous areas

8:05

of footprints, hyperextension.

8:07

The footprints dominate anteriorly with rotation

8:12

and translation alone or in combination

8:15

and offset between the sites

8:18

of footprints left behind.

8:21

And with flexion.

8:22

We can see these footprints of injury

8:25

that dominate posteriorly.

8:26

And here again are examples showing you impaction,

8:31

hyperextension, rotation and translation and flexion.