0:00

Hip.

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The hip is hard.

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The hip is big.

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The hip bears tremendous amounts of weight.

0:08

When you jump, 10 to 12 times your

0:11

body weight is exerted on the hip.

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While the hip is a large joint, it

0:16

has a very small capsule, thus making

0:20

diagnoses without contrast in the

0:22

joint that much more challenging.

0:24

Still, hardly ever do we put contrast in the

0:28

joint, and that's because we're experienced.

0:31

And today, and in a few subsequent vignettes,

0:34

I want to talk about sequences that will allow

0:37

you to avert putting contrast in the joint.

0:41

So let's start out with something very simple.

0:44

A plain old T2 spin echo

0:47

without fat suppression.

0:49

What do we use this for?

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Two major applications.

0:55

One, to characterize and analyze

0:58

ligaments, their thickness, and the

1:03

degree of attrition that is present or

1:06

not present, and the age of an injury.

1:11

You can lump together, with ligaments,

1:13

although not the focal point of the hip,

1:16

tendons and muscles, the same application.

1:21

Mostly for characterization, aging, and dating.

1:26

So, for instance, if we wanted to see the

1:28

character of the ligamentum teres as it inserts

1:31

on the fovea capitis, we might use the T2.

1:35

Not for diagnosis, but to see the character.

1:38

In other words, one bundle, two

1:40

bundles, acute, subacute, chronic.

1:45

The T2 weighted image also has

1:48

pretty good anatomic capability.

1:52

Most of the time, the T2 is used orthogonally.

1:55

In other words, straight up and down.

1:57

So if you look at the coronal

1:58

projection, the T2 will go straight

2:01

up and down as opposed to angled.

2:03

We don't typically use the T2 for discrete

2:06

measurements like the alpha angle.

2:09

The T2 in the hip, here, as elsewhere in

2:13

the body, when there's an effusion, when the

2:15

joint is wet, that is an excellent sequence to

2:20

characterize and locate intra-articular bodies

2:24

and also to differentiate intra-articular

2:27

defects, which are smaller and grayer in

2:31

synovial hyperplasia, but bigger and darker

2:36

when they're actual chondral osseous bodies or

2:39

primary or secondary synovial chondromatosis.

2:44

The T2 weighted image is deficient

2:47

in assessing labral pathology.

2:50

And it is extremely deficient at

2:53

assessing low-grade marrow pathology.

2:57

So it's not a great examination as a

3:00

primary sequence to look at tumors.

3:02

It's a good characterizer.

3:05

And it's also not very good at picking

3:07

up early, subtle bone injuries.

3:11

For a massive fracture, no problem.

3:13

Any sequence will do.

3:16

Let's look at the middle sequence.

3:19

And I'm only going to take three

3:20

sequences in this vignette.

3:23

The middle sequence.

3:24

Is a proton density fat suppression.

3:28

Spare, spur, special.

3:32

It's a frequency selective

3:35

form of fat suppression.

3:38

Unlike, unlike STIR, which

3:41

is non-frequency selective.

3:44

And this particular one is angled.

3:47

Let's look at it.

3:48

If you look on the far right and I

3:50

scroll it, you'll see it's angled with

3:51

the long axis of the femoral head.

3:54

The neck and the trochanteric region.

3:57

So it is not straight orthogonal.

4:00

That allows us to do several things.

4:02

First, the angle affords us our best look

4:05

at the labrum in the axial projection.

4:10

The angle also allows us

4:12

to measure the alpha angle.

4:15

Let's do that together.

4:17

On this axial oblique, we take a point in the

4:21

center of the femur and we bisect the femur.

4:26

And then on either side, some

4:27

refer to this as D1 and D2.

4:29

Thank you.

4:30

You don't really need to know much about that.

4:33

Then our second angle will go from your

4:36

perceived subjective evaluation of the head

4:39

neck junction, which is right here at this

4:41

curve, back to the center of the femur.

4:45

And this is your angle.

4:48

We like to see alpha angles

4:49

around 55 to 60 degrees.

4:53

When you have a bump that brings this alpha

4:55

angle up and increases it, there is an increased

5:00

risk or incidence of CAM-type impingement.

5:04

But it is not pathognomonic for such.

5:08

Now there are a few other useful

5:11

take-home points about the PD SPIR.

5:14

This is true in the hip and throughout

5:16

the rest of the entire body.

5:18

It is the sensitive detection

5:22

sequence for most general pathology.

5:25

It is sensitive for bone marrow infiltration,

5:29

infection, for fractures, and it also

5:32

is a very good all-purpose sequence for

5:35

ligaments, for labra, for the articular space.

5:39

for hyaline cartilage and even

5:42

for musculotendinous injuries.

5:45

You cannot perform a musculoskeletal

5:48

study in any part of the body without

5:51

having a high-quality, proton density,

5:55

frequency selective, fat suppression

5:57

sequence on a high-field scanner.

5:59

On low-field scanners, you'll use the STIR,

6:03

short time inversion recovery, as a substitute.

6:07

So we have it right in the middle.

6:10

Because this is your guts, the meat

6:14

and potatoes of your musculoskeletal

6:17

joint evaluation in any joint.

6:20

Now on the far right is a

6:22

simple T1 spin echo image.

6:25

It's so easy, any idiot can do it.

6:29

Any scanner can do it.

6:32

And what I mean by idiot is scanner,

6:34

low field, mid field, high field.

6:36

Now one counterintuitive fact about T1 imaging

6:41

is that at low field, 3, 25, 16, the T1 contrast

6:48

properties in the bone marrow are very low,

6:50

are actually better than they are at high field.

6:54

So if you were to have early edema

6:55

from osteomyelitis, it would show up

6:58

better on a low field scanner than

7:00

it would at a high field scanner.

7:03

A high field scanner has

7:05

superior spatial resolution.

7:09

This particular coronal sequence is orthogonal.

7:12

In other words, it goes straight front to back.

7:16

But you could angle it along the

7:18

long axis of the hip so that it goes

7:21

from anteromedial to posterolateral.

7:24

And many people do that.

7:26

And we'll talk about this type of angulation as

7:28

we get into sequences in a more complex fashion.

7:32

Now I use the T1 coronal much like I

7:35

would use a conventional radiograph.

7:38

It's an anatomy sequence.

7:40

I'm looking at the head neck junction cortex.

7:44

Yes, I'm looking at the bone marrow.

7:46

And T1 imaging is pretty sensitive for the bone

7:49

marrow, but not as sensitive as the PD SPIR.

7:53

It is highly useful for anatomic

7:57

contours, conformity, the matching

8:01

shapes of different structures.

8:02

In other words, does the acetabulum properly

8:06

cover the drop off of the femoral head?

8:09

What is the tapering of the head neck junction?

8:13

What is the status of the growth plate?

8:16

Is it open or closed?

8:17

It's closed.

8:18

Is there a scar?

8:20

Yes, there is.

8:21

For the inner half of the hip.

8:23

While T1 imaging is not a specific

8:28

sequence for ligaments and tendons, it

8:31

can be useful in assessing whether there's

8:33

swelling in the joint space, effacement

8:37

of the fatty pulvinar, or synovial

8:40

proliferation around the ligamentum teres.

8:43

Anytime there's fat, the T1-weighted

8:46

image becomes more important, as it does

8:49

in the marrow, as it does in the fat

8:51

within the joint in the fatty pulvinar.

8:53

This fatty space will widen in patients

8:56

with developmental dysplasia of the hip or

8:58

congenital absence of the ligamentum teres.

9:02

The T1 image is also very useful again

9:05

for contours, especially along the

9:07

lateral aspect of the greater trochanter.

9:10

People with notching, serration, or

9:13

irregularity of this area have the common

9:17

abnormality of gluteus medius tendinopathy,

9:21

tears, and bursitis, an oft-overlooked cause

9:26

of hip pain, especially in overweight women.

9:30

The T1-weighted image is less useful

9:33

for large intermediate areas of soft

9:35

tissue, like large muscle groups.

9:39

It is also useful for assessing the

9:42

subcutaneous fat in patients with inflammation.

9:45

It is an excellent reference sequence to

9:51

see what your other angles might have been,

9:54

as in this case where we have an angled

9:56

axial and a straight axial orthogonal axial.

10:01

So that, that initiates us into

10:03

three very basic sequences.

10:05

T2, PD SPIR, and T1 coronal.

10:10

In some of the other vignettes, we'll

10:12

talk about additional sequences,

10:15

their properties, their

10:16

usages, and their angulations.

10:19

Thanks.