0:00

Now with regard to some of the clinical aspects of tears

0:05

of the ACL, they're frequent in the United States,

0:09

obviously more than a million ACL injuries often reported

0:13

annually worldwide.

0:16

Typically seen in young persons, many of whom are athletic,

0:21

involved in a variety of sporting activities.

0:24

And as I've already mentioned,

0:26

female ath athlete athletes have a higher frequency

0:30

of ACL pair compared to male athletes.

0:34

And one of the important things I wanna mention again,

0:37

is these are often, in the majority of cases,

0:41

non-contact injuries.

0:43

There's no external contact.

0:45

There is a shifting someone running

0:47

and then shifts away trying to avoid an opponent,

0:51

for example, in American football.

0:54

That is often the cause of an ACL pair.

0:58

Now we come back to this chart that I showed you before

1:03

and I wanna kind of indicating where ACL appears

1:07

on this particular chart as a primary restraint

1:11

or as a secondary restraint.

1:13

And I'm indicating four important mechanisms of injury.

1:18

The ones in yellow are particularly important,

1:22

anterior translation of the tibia

1:24

and internal rotation of the tibia.

1:27

But valgus and hyperextension also can cause tears

1:31

of the anterior cruciate ligament.

1:34

But I emphasize anterior translation and internal rotation.

1:39

With regard to anterior translation,

1:42

the tibia moving anteriorly with respect to the femur,

1:46

there has been a lot of interest in the slope

1:50

of the articular surface of the tibia,

1:54

be it the medial tibial plateau,

1:57

or be it the lateral tibial plateau.

2:00

And here, for example, is how you might come up

2:02

with a measurement of tibial slope.

2:06

It is said to be a normal knees about eight to 10 degrees,

2:11

varying a little bit in the medial and lateral compartments.

2:15

Okay? It is, uh, increased purport

2:20

to be higher in adolescence with tears

2:23

of the anterior cruciate ligament.

2:26

An increased posterior tibial slope is also associated

2:29

with a variety of things, anterior translation of the tibia,

2:34

partial or complete tears

2:36

or retear of the anterior cruciate ligament.

2:40

So the orthopedic surgeon does have an interest,

2:43

at least some of them do in the pattern of sloping

2:47

of the proximal tibia.

2:49

And if it is exaggerated, which may in fact be associated

2:53

with a higher likelihood of ACL pairs.

2:57

Talking about anterior

2:58

Translation, there is a mechanism

3:00

that occurs in skiing called the boot induced mechanism.

3:06

I'm showing it here, taken from the internet.

3:08

Here's the history in this particular patient,

3:11

a 42-year-old recreational skier lost his balance.

3:15

During a jump, the tail of the downhill ski hit the snow,

3:19

pushed the back of the boot against the calf,

3:22

and then as a result of that,

3:25

he activated his quadriceps muscle,

3:28

translated his tibia in an anterior direction,

3:31

the ski continued running anteriorally,

3:34

he hurt a pop, he fell.

3:36

And here is the tearing of the anterior cruciate ligament

3:40

with rupture of the posterior capsule

3:43

and a tensile injury to the pop muscle.

3:47

The boot induced mechanism, anterior translation.

3:51

Let's look at internal rotation ery, as we discussed before,

3:56

but let's look at it in his gear taken from the internet.

4:00

This picture, here's the history

4:02

for this particular patient.

4:04

The downhill ski of this young man caught an outside edge

4:09

and he tumbled over it, something like this.

4:12

So we're seeing what is internal rotation

4:15

of the tibia associated with flexion of the knee

4:20

and a varis valgus stress.

4:22

And the result, as we've talked about classic for aery,

4:26

is a sigon fracture.

4:28

I.