0:00

Now let's look at the knee joint.

0:02

In the knee joint there are three axes of movement,

0:05

and in each of these axes, there is both angular

0:09

and translational movement.

0:10

Let me show you those three axes.

0:13

The first of these is a horizontal axis shown

0:16

by the orange tube.

0:18

The angular movement

0:20

that takes place in this particular plane would be

0:23

flexion and extension.

0:25

The second plane is one that runs from the front to the back

0:29

of the knee, an antral posterior plane.

0:32

And the angular movement that takes place in this plane goes

0:35

by a variety of names.

0:37

Abduction, abduction, valgus,

0:39

varus would be the angular movement.

0:42

The third imaging plane shown

0:44

by the blue tube runs from the top to the bottom

0:48

of the knee, a superior inferior.

0:50

And here the angular movement is external

0:53

and internal rotation.

0:55

So these are the axes of movement, the three axes

1:00

involved in the knee with both angular

1:03

and translational movements possible in each

1:06

of these three axxis.

1:08

Now, I know your first look at this would suggest this is a

1:11

complex slide, which it is, but it is an important slide.

1:15

So let me try to explain why I have included it.

1:19

There are four columns of information here.

1:23

In the first column, I am showing you seven movements

1:26

or motions that might take place in the knee.

1:30

Here I'm showing you varying angles of flexion for some

1:35

of those movements, and then I'm showing you the primary

1:38

restraint or resistance to that particular movement.

1:42

Then one or more of the secondary restraints or seen.

1:47

So the reason I mentioned this

1:49

and wanted to put this in is if you can find footprints,

1:52

which we'll discuss in a little while, that tell you

1:56

what motion or movement has taken place,

1:59

be it an abnormal movement during an injury.

2:02

The first structure that typically fails is the primary

2:06

restraint, and then one

2:08

or more of the secondary restraints may fail.

2:12

So the footprints help you decide what sort of mechanism

2:16

of injury, what abnormal movement has taken place.

2:20

Now, I'll just show you a couple examples

2:22

of how this might work.

2:24

Here I'm showing you a valgus movement or motion.

2:27

Typically, in the normal knee, the point of contact is,

2:32

or the axis is in the central part of the knee.

2:36

When we have a valgus movement, what we see is a shift

2:39

of that with contact.

2:41

Now occurring in the lateral compartment.

2:44

Here would be the site of compression, that green circle

2:48

at the site of compression,

2:50

we can have cartilage abnormalities.

2:52

I'll talk about those on on the Friday.

2:55

We can have subc chondral bone plate

2:59

Or subcon bone abnormalities,

3:01

and we can have meniscal pathology.

3:04

Everything to the left side of that point

3:07

of contact is under increased tensile force.

3:12

Now, the moment arm

3:13

of the medial supporting structures over here, alright,

3:18

is longer than the moment arm of the cruciate.

3:21

So the medial supporting structures tend to be the primary

3:25

restraint to a valgus movement, and one

3:28

or both cruciate ligaments,

3:30

particularly the anterior cruciate ligament,

3:34

represents the secondary restraint.

3:36

A typical valgus injury shown here

3:39

with the medial supporting structures injured

3:42

and the typical bone abnormalities present.

3:45

So that is what occurs when we have an

3:47

abnormal valgus movement.

3:49

Let's look at anterior translation.

3:51

When we deal with abnormal anterior posterior translation

3:56

of the knee, those ligaments oriented along the axis

4:00

of movement will be the most important stabilizers.

4:04

So here we can see with anterior translation

4:07

that the anterior cruciate ligament is the major

4:11

stabilizer here, a complete tear involving

4:15

the anterior cruciate ligament.

4:17

We'll get back to these patterns

4:19

of movement a little bit later.