0:00

<v ->So let's move on

0:02

and continue our discussion on osteonecrosis.

0:05

I'm gonna look now at the target site of the femoral head

0:10

because that's the classic prototype

0:13

now, just so you're aware a little bit

0:16

of the biomechanics of the femoral head

0:20

you'll note here that the femoral head itself

0:23

is offset to the femoral shat

0:27

and because in fact, there's an offset of the force,

0:30

there's a lot of tensile force that is produced

0:34

in the femoral neck, a lot of sheer forces

0:37

and that explains why we have

0:38

both prominent compressive as well

0:41

as prominent tensile trabeculae

0:45

within the proximal portion of the femur.

0:48

So I wanna spend a little bit

0:50

of time just showing you those trabeculae

0:52

so you're aware of them.

0:54

There are five groups of trabeculae

0:58

You can see them here.

0:59

This is the primary compressive group.

1:02

You kind gonna follow them as I show you

1:04

they're numbered the same in the specimen radiograph.

1:08

This is the primary compressive.

1:10

This is called the secondary compressive group

1:13

of trabeculae.

1:15

There's a separate group

1:17

within the greater trochanter labeled number three.

1:20

And then we have primary

1:22

and second tensile trabeculae

1:26

labeled numbers four and five.

1:29

And this produces a meshwork

1:32

of trabeculae within the femoral head and neck.

1:34

And I have an interest in that.

1:37

So if we look at it

1:38

it's kinda looks like this with trabeculae crossing.

1:42

Some people would argue they cross at right angles,

1:45

They may, they don't always cross it right angles

1:48

but you get the idea

1:50

that there are many trabeculae

1:52

that are crossing particularly in this region

1:55

that I've indicated in this specimen

1:58

and that's of interest to people

2:02

who have UCT

2:04

to try to diagnose osteonecrosis.

2:07

This is what the normal asterisk looks like.

2:10

If you do a transfer section of the femoral head

2:13

you see these trabeculae crossing,

2:16

there's a meshwork and you can see what it looks like.

2:19

And if you go ahead and radiograph that,

2:22

you can see this kind of crisscross trabeculae pattern

2:27

but normally as you looked at it

2:30

the area of increased density does not extend

2:35

out to the surface of the femoral head.

2:38

So in the normal situation

2:40

it kind of looks centered within the femoral head.

2:43

So many years ago, before MRI came along,

2:47

we used CT looking at transverse sections

2:51

and studied the asterisk to see

2:53

if in fact it was exaggerated.

2:56

And if it was exaggerated

2:57

we called this the positive asterisk sign

3:00

and you can see in that particular case

3:03

the trabeculae region now extends all the way

3:06

out to the surface of the femoral head.

3:09

That was always considered positive.

3:12

And we were diagnosed

3:13

by CT osteonecrosis involving the femoral head.

3:18

Now, the reason that the femoral head is vulnerable

3:22

with osteonecrosis

3:23

includes course a vulnerable blood supply.

3:27

The arterial supply comes

3:30

from medial and lateral circumflex arteries,

3:31

I've labeled them here for you

3:34

which themselves are derived

3:36

from the profunda femoris artery.

3:39

And as they extend laterally,

3:41

they in fact produce a retinacular vasculature

3:47

that produces rings.

3:49

And you can see these rings here.

3:51

And then the blood vessels extend

3:54

up along the femoral neck to reach the femoral head.

3:58

The most important supply comes

4:02

from the medial synovial fold

4:04

that I spoke about a couple of days ago

4:07

named after Amantini

4:10

and although some people call this a plica

4:13

this is a fundamental source

4:15

of blood supply to the femoral head.

4:18

You do not resect that as an abnormal plica.