0:00

The first case we're going to tackle is an 18

0:02

18-year-old woman with a chronic wound following

0:05

a Lisfranc ligament repair, and now she's

0:08

complaining of increased drainage and pain.

0:11

This is one of the more common

0:13

problems that MRI has asked to solve.

0:16

One of the reasons why I wanted to show it

0:19

is because it's a problem that MRI can solve

0:22

in a way that no other modality can solve.

0:25

And that is with a very high level of sensitivity

0:29

and a very high level of specificity and an

0:32

almost 100 percent negative predictive value.

0:36

And what I mean by that is, if you perform a

0:38

STIR or a water-weighted MRI, a SPUR, a SPARE

0:43

a special, a STIR something fat suppressed.

0:46

If there's no edema in the bone, it is

0:48

impossible, scientifically impossible,

0:51

for the patient to have osteomyelitis.

0:54

So that's it.

0:55

That's an excellent rule out.

0:57

So the water-weighted image is to

0:59

guide you as it relates to sensitivity.

1:03

But in terms of specificity, we all

1:05

know that lots of things can produce

1:07

edema and bone contusions tumors.

1:12

Inflammatory reactions such as RA, juxta

1:15

articular osteoedema is very common in RA, but

1:19

very few things will actually destroy bone.

1:22

In other words, reduce the cortex and

1:27

the architecture of the bone to nothing.

1:29

You can see that has happened here on the T1

1:32

weighted image, and it's the T1-weighted image

1:35

that you use to decide what that edema is from.

1:40

So you're looking at the zone of transition,

1:42

which for the most part is actually pretty narrow.

1:45

For instance, look at this tract

1:47

where they did a Lisfranc repair.

1:50

Um, this is a tract for a fixation

1:53

device for anchors, uh, and suture anchors.

1:57

And it's got a pretty sharp sclerotic

1:59

edge, so it doesn't look that disturbing.

2:03

Now, most people know that do this for

2:05

a living, when you take a screw or a

2:08

bioresorbable anchor, you put it in,

2:09

it is resorbed within 6 to 9 months.

2:12

And what goes into that spot,

2:15

what goes into that spot is fat.

2:18

So unless you knew how old this

2:19

was, this alone is not a problem.

2:23

It might get your attention because it's

2:24

very fluid-like, but it's not a problem.

2:26

Now, the fact that there is

2:28

extensive edema throughout the base of

2:30

the first metacarpal, sorry, metatarsal.

2:34

That is a huge problem.

2:36

There's, there's no explanation for that.

2:37

So that should at least worry you.

2:40

And then when you look at the, the, um, more

2:44

distal images, you know, when you think of

2:46

somebody who's had, say, a fixation device put

2:50

into anything, whether it's a shoulder or the

2:52

knee, it's going to look something like this.

2:58

It's going to be an anchor.

3:00

It may be bullet-shaped.

3:02

It may have screws associated with it,

3:04

with threads, but it doesn't look round.

3:08

Nothing that you put in the

3:09

extremity is going to look round.

3:13

So now when you go and look at this anchor

3:15

right here, there is a floating area

3:18

of anchor tissue and suture material.

3:23

And here it is.

3:25

And even though you do have a pretty sharp

3:27

edge to it, it's too big and it just blows

3:30

its way out into the soft tissues and enters

3:34

the subcutaneous area where it is draining.

3:38

So the history is supportive.

3:40

The shape of the lesion is supportive.

3:43

There's no other explanation that you

3:45

could give, uh, that would explain this

3:48

widening that you have here a hemorrhage.

3:52

First of all, it's not the signal of blood.

3:55

Lymph wouldn't do that.

3:56

An epidermoid.

3:58

Well, that would be a very unusual diagnosis.

4:00

It wouldn't explain the drainage of this patient.

4:04

It's also not a great shape for an

4:06

epidermoid, which is almost never

4:08

round and more often lobulated.

4:11

So you're really left with no, no other diagnosis

4:14

other than an abscess at the operative site.

4:19

Now let's look at the short-axis projection.

4:22

This is a scout.

4:23

Let's put up the short-axis T2, and I

4:27

really don't use a lot of T2 imaging

4:29

for infection, but I'll tell you where it

4:32

comes in extremely handy when the entire

4:36

extremity is just an unmitigated mess.

4:39

You know, you have a Charcot foot.

4:41

You have massive trauma.

4:43

You're trying to sort out an osteo.

4:45

There are very few things that are

4:48

going to be bright on a T2, on a

4:50

regular T2 without fat suppression.

4:53

Only things with extreme swelling

4:55

or extreme fluid collections.

4:57

So in a Charcot foot, which this is not, by

5:00

the way, the foot will turn very dark from

5:03

the sclerosis and the reactive bone formation.

5:06

Whereas an abscess.

5:08

will stick out or destructive

5:11

osteomyelitis will stick out.

5:14

So this is an abscess, and you can appreciate

5:18

how the abscess has blown into the soft tissues.

5:21

It is the source of drainage into the skin.

5:25

So the T2 simply reaffirms

5:27

what we already knew.

5:28

Now we have another problem, and that is

5:31

our abscess is not just in the in the

5:37

first. It's gone into the cuneiform.

5:40

It's gone into the base of the

5:41

second, and it also has some floating

5:46

anchor and suture material in it.

5:48

So we have actually two bones

5:51

that are affected by this process.

5:54

And we have two drain its sites.

5:56

We have one drain its site over here that

5:58

may or may not be going through to the skin.

6:01

We have another drain its site that

6:03

is clearly going through to the skin.

6:07

So, you know, resection is not really an option.

6:11

What are the options for this young girl?

6:14

The options are, of course, antibiotics,

6:16

but they're going to have to put direct at

6:18

they're going to have to bathe this, take

6:20

everything out, lavage the holes or the tracks.

6:25

They're going to have to put antibiotic beads

6:27

in after they lavage it with antibiotics.

6:30

And then this patient is going to have to

6:31

be on IV antibiotics for somewhere between

6:34

eight and 20 weeks with a PICC line.

6:39

Now I want to show you, I'll

6:42

put up the T1 one more time.

6:45

And you can see just how irregular, uh, this

6:49

abscess is and how it has a sclerotic edge,

6:53

which is, which indicates a high degree

6:56

of, of chronicity associated with this.

6:59

This is not your typical osteomyelitis.

7:01

However, this is one that's more

7:03

chronic that is dominated by an abscess.

7:06

And let me show you one that is

7:08

more typical of an osteomyelitis.

7:11

First of all, when you have osteomyelitis,

7:14

especially with typical organisms,

7:16

it looks like a bomb went off.

7:19

And here's what I mean.

7:21

So this is a different patient, and I don't

7:25

think the history really matters here.

7:27

So I'm going to put up, um, the

7:32

sagittal water weighted image.

7:34

We'll start with the first, then the second.

7:38

There's, by the way, your plantar plate.

7:40

Just beautiful.

7:42

There it is right there.

7:43

This curvilinear black thing

7:44

right there is the plantar plate.

7:49

Let's keep going, shall we?

7:52

We're in the third now and now we're in

7:55

the fourth and now we're in the fifth.

7:59

So the fourth looks a little

8:02

bit swollen there, doesn't it?

8:06

Let's keep looking.

8:07

Shall we?

8:08

Let's go to a long axis view.

8:19

So this patient has diffuse soft tissue swelling.

8:23

Let's look at the fourth.

8:24

There was a little bit of edema on

8:26

one of the water weighted sequences.

8:29

This was a patient with

8:30

cellulitis rule out osteomyelitis.

8:34

The T1 weighted image is negative.

8:38

The remaining water weighted sequences

8:41

are negative, and the patient has diffuse

8:44

interstitial swelling of the soft tissues.

8:47

So this is one where osteomyelitis was suspected,

8:51

but not found, and you could easily as part of

8:54

your practice, just perform a T1 weighted image.

8:59

Now, the only reason to perform more

9:01

than a T1 weighted image would be to

9:04

sort of isolate an abscess for biopsy.

9:05

But look at this ulcer right here.

9:08

You can see how close it is to the

9:10

bone of the fourth right there.

9:13

Now it doesn't invade the fourth.

9:16

It doesn't destroy the bone.

9:19

So this one you could say, does not yet have bone.

9:23

osteomyelitis.

9:24

One other comment I'll make is when you have

9:26

osteomyelitis, the bone is almost almost erased.

9:33

you'll completely lose the cortex of the bone.

9:37

So you actually will not see the

9:38

cortical outline of bone at all.

9:41

So you'll actually see gray signal intensity,

9:44

replace the architecture of the bone and

9:46

it'll look like the bone is completely erased.

9:50

Do you need a water weighted

9:51

image to assess bone marrow edema?

9:53

You do need a water weighted

9:55

image to assess bone marrow edema.

9:58

But I was making the point that if you wanted

10:00

to do a tailored five-minute examination

10:02

rule out osteo, you could do a T one weighted

10:06

image and that would give you the answer.

10:08

If you see nothing on the T one, it's not osteo.

10:11

Now that doesn't mean you couldn't have a

10:12

stress injury or some other stress phenomenon.

10:16

And, um, so every, every MR of

10:19

the extremity always includes.

10:22

Um, a water weighted image and not.

10:26

A T2.

10:27

Now you can include a T2, but the guts of

10:32

orthopedic MRI is the proton density fat

10:36

suppression image with a TE between 40 and 50.

10:40

Now a common mistake is to make that TE 20.

10:46

It's called proton density fat set.

10:48

So when you think of proton density,

10:49

you think long TR, short TE.

10:52

You don't want the TE too short.

10:54

Because that affects your tissue contrast.

10:56

You want the T right about 45 at 1.

10:59

5 T is the sweet spot, 50 at 3 T.

11:04

And if you go much beyond that, now

11:06

you're into T2 imaging and you're going

11:08

to be less sensitive to shifts in water.

11:11

So, every standard orthopedic MRI

11:13

has a proton density, fat set.

11:16

Proton density spur, spare, special, they all

11:19

mean the same thing, and everyone has a T1.

11:25

T2s are optional, but they usually are

11:26

included on most orthopedic MR studies.

11:29

Bone marrow edema is best seen on proton

11:32

density fat suppression imaging.

11:34

It is the detector sequence.

11:37

The T1 is the specificity sequence.