0:00

So let's first talk about a femoral cause

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for femoral acetabular impingement.

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This is a pattern

0:08

of impingement seen in young athletic persons typically

0:12

leading to limited internal rotation at the hip

0:16

with a positive impingement test.

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And this is how that impingement test is undertaken.

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This is cam impingement, pistol grip deformity,

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femoral waste deficiency.

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Let me explain some of those terms.

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This is what the normal hip looks like, uh, on a radiograph.

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This is what a cam type morphology might

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look like where there is prominence

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and even convexity along the lateral

0:45

and anterolateral aspect of the femoral head neck junction.

0:50

This was designated femoral lateral

0:53

femoral waste deficiency.

0:54

This being the femoral waste,

0:56

this was the lateral waste deficiency

0:59

and hence that was a term that was applied

1:01

to this particular pattern of deformity early on.

1:06

We now know this is cam impingement.

1:09

It was called a pistol grip deformity

1:11

because of its resemblance to

1:14

what some pistol grips look like.

1:17

This is a terrific picture

1:19

and I'm gonna come back to it a little bit later

1:22

because there's another finding illustrated

1:24

by this particular pistol grip.

1:27

But you can see how it resembles the bump

1:30

that's occurring on the antral lateral aspect

1:33

of the femoral head neck junction.

1:36

So we found this bump

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and then the question would, is there any measurement

1:41

that would help us document whether in fact we were dealing

1:45

with femoral sided femoral acetabular impingement

1:49

and utilizing axial blike images

1:51

that are programmed along the axis of the femoral neck?

1:56

You would end up with an image like this

1:58

and from that image you would establish an angle,

2:02

which was called the alpha angle.

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And the alpha angle was formed

2:07

or uh, created by first finding the center

2:12

of the femoral head

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and drawing a best fit circle of the femoral head.

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And then your next job was to draw a line from the center

2:21

of the femoral head along the axis of the femoral neck.

2:25

In some recent articles,

2:26

people have suggested drawing other circles here

2:29

and here, finding the middle

2:31

of those circles better constructing this particular line.

2:35

So that's one of the lines that you utilize.

2:39

The second line is to the area of the femoral neck that is

2:44

outside of the circle.

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And by drawing that line,

2:47

and here you can see a little bit of the abnormal bone

2:50

outside of the circle,

2:51

you've established an angle which is called the alpha angle.

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The normal initially

2:58

Was said to be less than 55 degrees,

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where an abnormal angle would be one

3:03

that is greater than 55 degrees.

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So this is what it would look like. Diagrammatically.

3:10

Here's an example showing you the alpha angle.

3:13

The normal less than 55 degrees in the middle.

3:17

An abnormal alpha angle here with a, this one

3:21

measured at 78 degrees.

3:23

So this was a way that we were able to figure out an angle

3:27

that might tell us, you know, the morphology of

3:30

that femoral head and neck junction,

3:32

particularly in anteriorly is abnormal.

3:36

The alpha angle is abnormal.

3:38

Now through the years we've learned this is not an ideal

3:41

measurement for a number of reasons.

3:44

It varies according to the imaging plane

3:46

and oblique slice selection.

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So the question is, which oblique slice do you utilize?

3:53

It varies among readers.

3:54

That's been shown in several articles.

3:57

The alpha angle has been suggested to be abnormal

4:00

with angles that have varied from as low as 50 degrees

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to 83 degrees.

4:06

All right, so clearly some variation in what is considered

4:10

to be an abnormal angle.

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It's abnormal in asymptomatic persons.

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And as shown in this particular case here,

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it can be normal in symptomatic persons.

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Here's a person who had his symptoms related to cam type

4:25

impingement with a large bump, right?

4:29

You can see the bump with the arrow here and here

4:33

and you can see it here.

4:35

But when we draw the al the uh, alpha angle,

4:38

because the bumps a little bit lower, we end up

4:42

with a 50 degree alpha angle, which is a normal alpha angle.

4:47

So although the alpha angle is a guideline,

4:50

it is not a foolproof rule, uh, in terms

4:53

of identifying cam type impingement.

4:56

And I'm gonna introduce another problem that we have

5:00

when we're talking about primary cam type morphology.

5:03

We're supposed to be talking about developmental bumps,

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but many of the bumps

5:08

that we see along the head neck junction will lead

5:11

to osteophytes.

5:13

This is an abnormal bump.

5:15

This bump could produce an abnormal alpha angle,

5:18

but there's the original zone

5:20

of calcified cartilage telling me

5:22

that this is not developmental.

5:24

This is an acquired bump.

5:27

This patient already has osteoarthrosis.

5:30

So although there is a labral pathology

5:32

and cartilage delamination in this case,

5:36

this is an acquired bump

5:38

and not compatible with primary

5:41

cam type femoral acetabular impingement.

5:45

Now there's another finding that has been associated

5:49

with cam type impingement

5:51

and that is the synovial herniation pit.

5:55

I know about this particular

5:56

Finding from my association, my good friend Michael Pitt,

6:01

and we used to call it Pitt's Pitt.

6:03

He and others at the University

6:05

of Arizona described this many, many years ago.

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And in that article where they were looking at specimens,

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they said this was a commonly acquired degenerative change

6:17

developing on the surface, the ant, uh, superior surface

6:22

of the femoral neck in an area

6:24

where the bone was often roughened.

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This is what it looked like.

6:28

So this in no way was diagnostic of impingement.

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At least that was the belief it was found in normals

6:35

with minor degenerative changes.

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Now, just for clarification,

6:40

when this was described back in 1982,

6:43

femoral acid tabular impingement was not a well-known topic.

6:47

And so it could be that some

6:49

of these specimens may have had these herniation pits

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because in fact they were derived from persons who did have,

6:58

uh, cam type femoral acetabular impingement.

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But there are articles such as this one

7:05

that I'm quoting here in the Korean Journal of Radiology

7:08

that have said the prevalence, uh, the prevalence

7:12

of herniation pits in asymptomatic persons is as high

7:15

as 22%

7:17

and they found no association of an abnormal alpha angle

7:21

with the presence or size of a herniation pit.

7:25

So once again, a bit of a controversial finding.

7:28

Now, one of the interesting aspects about the cause

7:32

of cam type developmental morphology is a relationship

7:37

to physio closure.

7:39

It's been shown in fact that the pistol grip type morphology

7:43

often occurs just

7:45

before the time of physio closure, all right,

7:49

and that the alpha angles may increase at that time.

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So we go back to this particular pistol grip.

7:55

This is the fsis.

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And when you have a developmental rather than acquired bump,

8:02

that FSIS or physio scar should extend all the way out

8:06

to the lateral surface at the femoral head NED junction.

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So there is accumulating evidence

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that developmental cam type morphology relates

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to an alteration in the growth plate,

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particularly in those people involved in sports.

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And it is suggested it's related to delayed closure

8:28

of the anterolateral aspect of the fsis.

8:31

So the physio line appears elongated

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and goes all the way out to the surface.

8:38

Here's a nice picture taken from the literature showing you

8:41

a developmental bump, which is intimate

8:44

with the lateral aspect of the fsis, possibly related

8:49

to delayed closure

8:51

and continued growth involving the lateral

8:54

Aspect of the femoral head.

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So this may be the real cause

8:59

of cam type developmental femoral acetabular impingement.

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So if we take the normal situation, okay,

9:08

which we're seeing here,

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and we add cam morphology, you can imagine in certain

9:16

movements of the hip that bump could contact the labrum lead

9:21

to labral tearing or labral detachment.

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And this sort of phenomenon has been likened to a cam,

9:28

which is a rotating piece in a mechanical linkage that

9:33

transforms rotary motion into linear motion, hence,

9:37

hence the term cam type morphology.

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Now just to finish up cam morphology, I would tell you

9:44

that there are a variety of cartilage abnormalities

9:47

that can be associated with cam type morphology.

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I'm listing three of them here.

9:53

I'm demonstrating type three, which is cartilage,

9:56

delamination, and labral tearing this one occurring in

10:00

a cric hip.

10:02

This has been suggested to relate to outside in vector

10:06

of pathology to see the cartilage.

10:10

Well though traction may be necessary,

10:13

particularly when combined with a joint effusion or Mr.

10:17

Arthrography and another example,

10:20

this is a type four lesion.

10:23

All right, cartilage, deamination and label detachment.

10:27

This might represent an inside out vector mechanism.

10:32

You can see here the labral detachment.

10:35

In some cases, the paralabral recess can enlarge.

10:38

We see the labral tear or labral separation quite well.

10:43

So there are articles that have

10:45

emphasized these two mechanisms outside in on your left,

10:50

inside out on your right, suggesting that

10:53

outside in was seen with primary cam morphology

10:58

and hip dysplasia more often is an inside out

11:02

mechanism vector mechanism.