0:00

We're gonna make another move in a distal direction,

0:04

move now from the elbow to the wrist

0:06

and spend these hours,

0:09

these three hours dealing with the wrist.

0:12

Now I know, and I think I've already indicated

0:14

that the audience is a mixture of those

0:16

who are very experienced in MRI

0:20

and those who are perhaps just beginning

0:23

to learn the important aspects of this imaging method.

0:28

And I say that again at this point

0:30

because of all the lectures

0:32

that I am giving in this particular conference,

0:35

this is the one that is probably the most difficult,

0:39

the most complex.

0:41

We're gonna be dealing with a lot of an anatomy

0:44

and anatomic structures who have long names, who have names

0:48

that are not consistent.

0:49

Sometimes from one site to another.

0:52

We'll be dealing a little bit with biomechanics.

0:55

We'll be talking about classification

0:57

and patterns of injury with emphasis on MR Imaging.

1:02

And just to show you the overall organization

1:05

of this lecture, you can see here we have a lot to cover.

1:09

Begin briefly with risk biomechanics.

1:12

We'll move on to some general ligament anatomy,

1:15

talk a bit about lesions of intrinsic

1:18

and extrinsic ligaments.

1:19

And then, and for the most important part, we'll talk about

1:24

definitions and patterns of carpal instability.

1:28

So let's go ahead and get started.

1:30

I want to introduce you to the three major articulations

1:34

of the wrist, often called compartments

1:37

that we'll be dealing with in this uh, lecture.

1:41

The first is the radial carpal compartment C shape

1:45

separating the distal radius from the proximal carpal row.

1:49

And you can appreciate that.

1:50

Generally we see a convex carpal surface articulating

1:55

with a concave surface of the distal radius.

1:59

If you look closely at the architecture

2:01

of the distal radius, you will cease

2:04

two normal depressions called fate, the scaphoid fossa,

2:08

and the lunate faucet.

2:10

The lunate fce, which I won't be uh, talking about,

2:15

is involved in certain fractures of the distal radius.

2:18

One type called a die punch fracture.

2:22

The scaphoid fossa is gonna be important in certain aspects

2:25

of this particular lecture because it may become enlarged

2:29

and depressed in certain conditions.

2:33

I wanted to illustrate that right at the outset.

2:35

At the far right of this slide, you can see

2:38

with scapholunate advanced collapse slack risk,

2:42

which we'll talk about later, that there's narrowing

2:45

between the radius and scalid

2:47

and deepening of that scaphoid foa and above it.

2:51

And very similar is what you would get with the arthropathy

2:55

of calcium pyrophosphate disease.

2:58

The similar findings

2:59

with a little bit more disorganization occurring in the mid

3:03

carpal compartment, but we'll get back to

3:06

that a little bit later.

3:08

The second compartment

3:09

with which we will deal is the mid carpal,

3:12

a trans carpal joint or compartment.

3:15

It has a very complex shape as you can see on the left

3:18

with a white line in some aspects convex

3:22

and other aspects concave.

3:24

And on the right it becomes saddle shape.

3:28

Now this is an important compartment separated from the

3:31

radial carpal compartment normally

3:33

by the interosseous ligaments of the proximal carpal row.

3:38

It's of interest. There's one variation

3:40

that does have some clinical importance.

3:43

There are two types of distal articular surface

3:46

of the lunate in type one shown at the top.

3:49

There is a single articular surface, one facet.

3:54

As you look at type two,

3:55

you can see in fact there are two facets in the distal

3:59

surface of the lunate.

4:02

Type one predisposes to several conditions.

4:05

I've listed them there.

4:07

Type two predisposes

4:09

to other conditions which I have listed.

4:11

We'll be discussing some of them later on in this lecture.

4:16

The third compartment

4:18

or joint that I want to emphasize is the common

4:21

carpal metacarpal joint.

4:23

It separates the distal carpal row from the basis

4:27

of the four nar metacarpals.

4:29

And then you can see by the orange arrows

4:32

that extends more distally communicating

4:35

with inter metacarpal compartments.

4:37

The first carpal metacarpal compartment is indicated in

4:41

green, green arrows.

4:43

It does not articulate

4:44

or communicate, I should say, with the other portions

4:47

of the common carpal metacarpal joint.

4:50

I won't be talking a great deal about

4:52

that compartment other than in

4:54

to indicate there are multiple important ligaments

4:58

that stabilize the first carpal metacarpal compartment.

5:03

I wanna make one important diagnostic point about it

5:07

shown on your left side.

5:09

At the bottom of this slide taken from the literature is the

5:12

normal appearance on a PA radiograph of this area.

5:17

You should be able

5:18

to see the common carpal metacarpal joint.

5:22

It has the shape as indicated there of a parallel M.

5:26

Now look at the images on your right.

5:29

This is a dorsal fracture dislocation obvious on

5:33

the lateral radiograph.

5:34

But I am telling you, you can make the diagnosis on the PA

5:38

frontal radiograph because that normal

5:41

parallel M sign is no longer visible.

5:43

It's obliterated

5:45

because of the abnormal alignment

5:47

between the distal carpal row

5:49

and the basis of the four nar metacarpals.

5:53

Now let's talk very briefly about normal wrist

5:56

Movement. It is complex

5:57

and it is controversial.

6:01

In general, it is believed that little motion exists

6:04

between the bones of the distal carpal row.

6:08

They move, but they move as a unit.

6:11

With regard to the proximal carpal row labeled two here,

6:14

there are no significant muscle attachments.

6:19

So the movement of the proximal carpal row is based upon

6:23

their sensing what is going on with the distal carpal row

6:27

and it will move accordingly.

6:30

And with that, that there are certain ligaments,

6:33

particularly those ligaments that cross the mid carpal joint

6:37

that may be susceptible to injury.

6:41

Now there's disagreement about which part

6:44

of the proximal carpal row reacts

6:47

to the movement in the distal carpal row, whichever it is.

6:50

It's called the intercalated element or elements.

6:55

I've indicated there that it could be any of these bones,

6:58

not the pisiform, but the three others in combination

7:02

or in alone, alone.

7:04

You will see various descriptions of this in the available

7:09

literature and that has led to three particular theories as

7:13

to the biomechanics and kinematics of wrist motion.

7:18

The oldest being the risk column theory in which there are

7:22

three independent vertical columns.

7:25

Wrist rows suggested a number of years ago

7:27

where we have a row like

7:29

or ring-like structure composed of the proximal

7:33

and distal carpal rows with substantial motion occurring

7:37

between the bones of each of those two rows.

7:41

And then the litman, uh, concept of an oval ring

7:45

with important ligaments that connect the two carpal rows,

7:49

especially the arcuate ligament,

7:52

which will become your friend in a few minutes.

7:55

Now let's go ahead and apply an axial load to the wrist.

8:01

I'm showing that with the blue vertical arrow at the top

8:03

of this slide and four motions occur.

8:08

Typically, there is pronation of the distal row, flexion

8:12

of the scaphoid and the opposite in the

8:15

triquetrum, which extends.

8:17

There's also lunate translation related

8:20

to the angular surface of the distal radius.

8:23

Now, when an axial load is applied to the wrist,

8:27

we can look at the distribution of force

8:30

across the radiocarpal

8:32

and radial ulnar portions of of the proximal wrist.

8:36

The major load is applied to the radio scaphoid portion up

8:40

to 50 55%.

8:43

The radio lunate portion can get quite a load here up

8:47

to 47%.

8:49

And the carpus TFCC

8:51

and ulna, a more minor load applied to it.

8:56

But the amount of load applied

8:58

to these three segments is dependent upon ulnar length

9:02

or ulnar variance.

9:04

And if in fact you have a short ulnar, the amount of force

9:08

that goes across the lunate radius portion

9:12

of this space becomes more dramatic.

9:16

This can lead to stress fractures involving the lunate,

9:20

a phenomenon that may lead to secondary osteonecrosis

9:24

and what you know as kBox disease.

9:27

So NAR length does in fact have a significant

9:32

importance with regard to

9:34

where the force is distributed across this joint.