Upcoming Events
Log In
Pricing
Free Trial

Wk 5, Case 2 - Review

HIDE
PrevNext

0:00

The first case we're going to tackle

0:02

is a 16-year-old with medial knee pain and instability

0:06

following an American football injury.

0:09

Of course,

0:10

there's European football and they are querying

0:14

an ACL tear.

0:16

So generally,

0:17

when I approach a knee case,

0:20

because the axial comes up first,

0:24

it's usually the first thing I look at.

0:26

I have a high volume of cases that I read during

0:29

the day, so I try and be as expedient as possible.

0:32

But if I had to say what the sequence is,

0:34

that gives me the most information.

0:36

as an experienced reader,

0:38

it's the coronal water weighted image.

0:41

So, I can usually tell everything that's

0:43

happening off that image alone.

0:45

But let's go in the order how I might go if I was

0:49

less experienced and I would start out with

0:52

the axial, I'd look at the patellar shape,

0:54

I'd look at the trochlear shape,

0:57

and then I would look at the

0:58

Medial Patellofemoral Ligament

1:00

and the lateral retinaculum.

1:01

I'd look for chondromalacia,

1:03

I'd look at the size of the effusion,

1:04

that gives me an idea whether anything's wrong.

1:07

And then after that,

1:10

I scroll and I read to the history,

1:13

and I always read to the history for every single

1:16

case, whether it's a spine, a liver, or a knee.

1:21

And in my head, I have this thought

1:24

that no matter what,

1:26

whatever the patient says is true.

1:29

There are very few patients who will malinger.

1:32

Maybe in a personal injury case

1:35

and maybe in a workman's compensation case,

1:38

but that's rare.

1:39

So the patient has a symptom.

1:42

There was always a reason for that symptom.

1:44

So I do read normal MRIs,

1:46

but I'm very uncomfortable when I do because

1:48

I know that there is something

1:50

there in most instances.

1:52

So, I continually drill mentally into the case

1:56

until I either find it or I've exhausted every option.

1:59

So here, we have an effusion.

2:02

And just looking at the axial,

2:03

I can tell right away,

2:04

because I'm reading to the history,

2:06

that in the axial projection,

2:09

I know that this is lateral,

2:10

because the patellar almost always tilts laterally.

2:13

So I can tell this is the lateral side,

2:16

and that means that the anterior cruciate ligament

2:18

is going to be on the lateral side.

2:20

So here's my posterior cruciate ligament,

2:22

somewhat round or oblong, fat and dark.

2:26

The ACL, not so much.

2:28

When I follow that ACL, it's fairly gray,

2:32

and I have a great deal of difficulty finding

2:34

it as a contiguous line from anteromedial

2:38

to posterolateral.

2:39

So, I already know that I have an anterior cruciate

2:43

ligament injury of some kind and that

2:45

it's likely to be high grade.

2:47

And this is what they were looking for.

2:49

I'm also looking at the collaterals.

2:51

I can see the lateral collateral

2:53

complex over here.

2:55

I'm not going to articulate all the anatomic

2:57

structures right now in this projection,

2:58

but I can see everything,

2:59

it's pretty dark.

3:01

On this side,

3:02

on the medial side, everything is not so dark,

3:05

especially anteriorly,

3:07

where the tibial collateral ligament lives,

3:09

right here.

3:10

And so, I'm suspicious of a medial

3:12

collateral ligament injury,

3:14

and I have yet to look at anything else.

3:16

I already know that the posterior cruciate

3:18

ligament because of its contour and its signal is intact.

3:22

So without even looking at any other sequence,

3:25

I now know that I have an anterior cruciate

3:28

ligament injury, an MCL injury, an intact PCL,

3:32

and an intact LCL.

3:35

And so,

3:36

I'm going into my next sequences with a lot of knowledge.

3:40

Because there's been a somewhat violent injury.

3:43

You know, it's a football injury.

3:44

It's a contact sport. There's an ACL.

3:47

There's an MCL.

3:48

I am discreetly checking the neurovascular bundle.

3:53

You know, if you miss an ACL,

3:54

not horrible.

3:56

If you miss a vascular injury,

3:57

horrible.

3:58

So, we're checking out the flow voids in the vessels

4:03

in the back and the artery, which is deepest,

4:05

and we're looking at the neurovascular bundle,

4:08

although usually the neurovascular bundle is not

4:11

injured, unless you have a varus insole.

4:14

In other words,

4:15

an injury to the lateral side of the knee.

4:17

So that's good news.

4:18

Let's turn our attention now

4:20

to the water-weighted sequences.

4:22

And this is really how I do it.

4:24

I go right to the water-weighted sequences,

4:26

because, again, for me, time is very important.

4:29

And I know for you, most of you are,

4:31

in private practice, time is very important.

4:34

And even outside of practice,

4:36

time is your most valuable asset.

4:38

So, we're scrolling back and forth.

4:40

We see that there are a series of bone injuries

4:44

which tell you the mechanism of injury.

4:46

First of all,

4:47

there is a microtrabecular injury of

4:50

the inferior patella.

4:52

Right there.

4:54

And what do I mean by microtubecular injury?

4:56

Anything other than a macro fracture.

4:58

Anything other than a visible fracture is a

5:00

microtubecular injury.

5:02

What's in that category?

5:04

Low grade contusion, high grade contusion,

5:07

microtubecular infraction,

5:09

and microtubecular fracture.

5:11

Those are the four stages before you actually have

5:14

a macro fracture.

5:17

So, what's a low-grade contusion?

5:20

You only see it on a water-weighted image.

5:22

What's a high grade contusion?

5:24

You see it on a water-weighted image

5:25

and a T1-weighted image.

5:27

What's a microtubecular infraction?

5:30

Little spidery lines that don't really involve the cortex.

5:33

What's a microtrabecular fracture?

5:35

Little spidery lines that do involve the cortex.

5:40

And then a macro fracture,

5:41

zigzag lines that go through the cortex.

5:44

So now, as we scroll back and forth,

5:46

we get an idea of what the mechanism of injury is.

5:49

We have an anterior femoral terminal sulcus,

5:52

microtubecular injury with slight depression and

5:55

a non-kissing lesion in the back of the tibia.

5:58

So what that means is, this is what happened.

6:00

The femur went back on the tibia with the foot in

6:06

external rotation and the tibia in internal rotation.

6:09

And basically, the tibia subluxed

6:12

relative to the femur.

6:13

And this impartial knee flexion

6:16

banged against that.

6:18

That takes a lot of force to do that.

6:21

So, when that happens...

6:23

Look at my fists.

6:24

The structures in the back will take a stretch.

6:28

They'll also take a compression.

6:31

So, this is a kid.

6:32

It's a young kid.

6:33

The structures are very pliable.

6:35

So to injure these structures back here

6:38

in a child, takes a lot of force.

6:40

So now let's go to the back of the knee,

6:42

and we're scrolling sagittally,

6:44

and we're looking specifically at

6:46

the posterolateral corner.

6:47

And we're very interested in the

6:49

popliteofibular ligament.

6:51

Now remember, I said I didn't see

6:54

a lateral side injury,

6:56

but the posterolateral and

6:57

posteromedial corners,

6:58

you really have to look at the sagittal projection.

7:01

So things look a little bit wavy and a little

7:03

bit stretchy, but they're intact.

7:06

Here is the arcuate ligament back here,

7:08

this little thin structure posteriorly.

7:10

Here's the popliteofibular ligament.

7:12

It's a little bit wavy right there,

7:14

but it's still present,

7:16

still inserts on the fibular head.

7:18

So, that's okay.

7:20

What's not okay is there should be two attachments

7:26

from the posterior meniscus.

7:28

There should be attachment up high

7:30

and an attachment down low,

7:32

and it pretty much goes all the way across from

7:36

lateral to medial, or from lateral to midline.

7:39

Now, let's have a look.

7:40

Let's scroll.

7:41

There's one of the attachments.

7:43

It's flopping in the breeze.

7:46

The other attachment is not visible either.

7:48

So, there is a meniscopopliteal fascicular

7:52

detachment from that stretch.

7:55

Some people might call this a

7:57

meniscocapsular separation.

7:59

I reserve that phrase for when the meniscus

8:02

actually displaces more than a centimeter to a

8:06

centimeter and a half, which hasn't happened here.

8:08

So, I'm just going to call it a meniscal vesicular

8:11

lateral detachment. Does that matter?

8:14

It absolutely does matter,

8:15

because the meniscus can start to do this.

8:17

It can start to turn on itself,

8:19

which is not great.

8:20

Then, as we go a little bit deeper, we see this.

8:23

Now, taking off from the lateral meniscus is a small

8:27

ligament called the ligament of Wrisberg.

8:29

I think we can see it right...

8:31

Let's see.

8:33

There.

8:34

On the coronal.

8:35

Now, that's a point of weakness.

8:38

So at that takeoff,

8:40

you can often get a little bit of a slit,

8:43

and you should have that slit appear

8:45

here normally.

8:46

So, normally,

8:47

the Wrisberg ligament would be separated

8:49

from the meniscus by this little slit,

8:50

and this would be the Wrisberg ligament.

8:52

So let's go in tight into the midline,

8:56

and here is your Wrisberg ligament.

9:01

And look at that interface.

9:02

Now, it's persisting.

9:03

It's still persisting.

9:05

It's persisting on too many slices.

9:07

It's still persisting.

9:08

So there is what we call a posterolateral

9:12

pivot shift Wrisberg rip injury.

9:16

Let's keep going, shall we?

9:18

Let's go to...

9:19

And there's the Wrisberg ligament,

9:21

behind the posterior cruciate ligament.

9:23

There's the Humphrey ligament in front

9:25

of the posterior cruciate ligament.

9:27

Now, let's go to the medial side.

9:29

On the medial side, in children,

9:32

I don't mind if there's signal in the outer third

9:34

of the meniscus. I don't mind at all.

9:36

But I don't want the signal to go like this.

9:40

I don't want the signal to go up and down.

9:42

I don't want the signal to hit the tibial surface.

9:45

And it does.

9:46

So, there's a very low-grade meniscal tear

9:50

posteromedially, right there.

9:52

And what would we do with that?

9:54

Absolutely nothing.

9:55

What would we do with the lateral meniscus?

9:58

The lateral meniscus,

10:00

we might have to tap down with sutures

10:04

because of its hypermobility.

10:05

So that'll be determined at surgery

10:08

when they take the meniscus and see how

10:10

hypermobile it is.

10:12

They won't sew this meniscus.

10:14

They will not repair that Wrisberg rip.

10:16

Let's go back over to the medial side.

10:19

Now with this huge stretch,

10:21

with this massive stretch that's

10:23

occurred in a child,

10:24

where the tibia is translated anterior to the femur,

10:28

the posteromedial capsule is under a stretch.

10:30

What gave way on the lateral side?

10:32

On the lateral side,

10:33

the meniscal vesicular attachment is torn.

10:36

But over here, the meniscocapsular reflection,

10:40

with its multiple short ligaments

10:42

that are hard to see, have been injured.

10:44

This is too swollen.

10:46

There is normally a meniscal posterior tibial ligament.

10:50

Here it is very stretched out.

10:53

That should attach over here.

10:56

So, this is known as a posteromedial ramp lesion.

11:02

Now, another thing that's happening.

11:04

The child is not even standing up.

11:06

Look at what's happening to the meniscus.

11:08

It is prolapsing posteriorly.

11:13

It's a little puffed out right there.

11:15

That's called a brake-stop mechanism injury

11:18

because the posteromedial stabilizers

11:21

at the meniscocapsular reflection are injured.

11:25

Now, a ramp lesion.

11:27

A ramp lesion is a stretch-type injury

11:31

that occurs at the meniscocapsular reflection.

11:35

And we only use this term posteromedially.

11:38

We don't use it anywhere else.

11:40

What are the five types of ramp lesions?

11:44

Well, the first type is this type

11:46

where you've injured

11:47

this posterior meniscal tibial ligament.

11:50

The capsule is swollen and there's nothing else

11:53

vertically orient it.

11:55

That would be a Ramp 1.

11:56

Then you have ramps 2 and 3

11:58

where you might have a vertical partial depth tear

12:01

from the top or from the bottom.

12:04

What's a 4?

12:05

A 4 would be when you have a line in the

12:08

meniscus going all the way from top to bottom.

12:11

What's a 5?

12:13

A 5 would be where you have a double tear

12:16

along with all this going on in the back.

12:19

So now we've got an ACL tear,

12:23

a Wrisberg rip injury,

12:26

a lateral menisco fascicular detachment,

12:29

injury to the brake stop mechanism with a ramp 1 lesion.

12:34

A tiny little, but mostly intra-substance tear

12:36

of the meniscus, we're not going to touch.

12:38

Let's go to the cruciate.

12:40

Let's zoom out.

12:42

And right there in the middle,

12:43

the anterior cruciate ligament stump.

12:46

The distal posterior cruciate ligament stump.

12:50

And there is a giant hole in the middle.

12:53

You can drive a large Toyota through that hole.

12:59

Posterior crucial ligament, as we suspected.

13:01

Fine.

13:02

All right,

13:03

let's go to the coronals and

13:05

look at the collaterals.

13:07

Popliteal origin, tendon origin, normal.

13:11

Fibular collateral ligament, intact.

13:15

Scant swelling, but intact.

13:18

The biceps femoris and conjoined insertion

13:21

on the fibular head, intact.

13:23

The medial collateral ligament, as we suspected,

13:27

torn anterior and proximal.

13:30

There's also a meniscofemoral ligament.

13:32

It's intact right there.

13:35

There's also a meniscotibial ligament.

13:37

It's intact right there.

13:39

When you get anteriorly,

13:41

this is known as the meniscopatellar ligament.

13:44

This should go towards the patella and it should

13:46

arc off towards the superomedial aspect of

13:50

the knee as it does.

13:51

This is normal.

13:52

That's normal. That's not a detachment.

13:55

All right,

13:55

let's look at the T1-weighted image for giggles,

13:58

because we're not going to get

13:58

a lot more out of it.

14:00

Now, I know in Aus, you guys do a lot of proton-density

14:04

imaging instead of T1 imaging.

14:06

I'm against that.

14:08

And you do it because it helps your visualization

14:11

of meniscal tears. But you don't need that.

14:13

If you combine the T1 and the proton-density

14:15

fat suppression, you don't need that.

14:17

And a proton density will obscure the

14:20

bone findings, including fractures,

14:22

including osteomyelitis.

14:24

So, I'd much rather have a true T1.

14:26

You can also see our very low grade

14:29

meniscal injury right there.

14:31

You can see our swelling and the slight

14:34

corrugation of the posterior meniscotibial ligament.

14:38

How are the growth plates?

14:39

They're open. They're fine.

14:41

That's important because it's a child.

14:43

To fix this ACL,

14:45

you want to avoid drilling through

14:48

open growth plates.

14:49

We have an effusion with a dilute hemarthrosis

14:52

with a little methemoglobin staining.

14:55

There is your fracture.

14:57

There is your fracture,

14:58

microtrabecular fracture with cortical involvement

15:01

in the posterior tibia.

15:03

You're not going to see that on an x-ray.

15:06

Then, you've got your ramp lesion on your medial side,

15:10

and you're pretty much done.

15:11

There is a T2.

15:12

It doesn't add much except showing you,

15:14

once again, the hole, the size,

15:18

the sheer absolute rupture of the mid portion

15:22

of the anterior cruciate ligament.

15:26

Now, there's one other finding here that's

15:28

a little bit confusing.

15:29

Some of the fibers of the anterior cruciate

15:31

ligament have folded down on themselves,

15:34

creating the impression of a mass right there.

15:37

So, that might be a little confusing.

15:39

You want to go back and make sure, see,

15:41

there's the ACL twisted down on itself.

15:45

You want to make absolutely sure you

15:47

don't have a bucket handle tear.

15:48

You look for meniscus truncated and separated

15:52

from itself into two pieces.

15:54

The patient does not have that.

15:56

That would completely change the management of

15:58

this case and how long you wait for surgery.

16:00

They will let this knee cool off.

16:02

They will try and repair the ACL while

16:05

avoiding the growth plate.

16:07

They will leave the medial meniscus alone.

16:09

They will test the lateral meniscus at surgery

16:12

to see if it needs to be tacked down.

16:14

They will leave the MCL alone.

Report

Patient History
16-year -old with medial knee pain and instability following a football injury. Query ACL injury.

Findings
Menisci:

Medial Meniscus: Thin vertical longitudinal tear at the meniscocapsular junction, consistent with a ramp lesion (ramp 1). Slightly prolapsed posterior meniscal root indicative of a “break stop mechanism” injury.

Lateral Meniscus: Delicate undersurface Wrisberg rip tear on several sequential images, from the Wrisberg meniscofemoral attachment extending into the posterior horn. Tear measures approximately 1 cm in length. No displacement.

Ligaments:

Anterior Cruciate Ligament: Complete ACL transection with interposed hemorrhage and debris between the torn fiber fragments.

Posterior Cruciate Ligament: Intact.

Medial Collateral Ligament: Diffuse periligamentous edema along the tibial collateral ligament with partial-thickness tear anteriorly, consistent with intermediate grade injury (grade 2).

Disruption of the anterior aspect of the meniscofemoral ligament.

Lateral Collateral Ligament: Intact.

Posterolateral Corner Structures: Mildly swollen popliteofibular ligament.

Posteromedial Corner Structures: Ramp 1 lesion. Mildly swollen but intact posterior oblique ligament.

Extensor Mechanism:

Patellar Tendon: Intact.

Distal Quadriceps Tendon: Intact.
Medial Patellofemoral Ligament: Intermediate to high-grade tear of the femoral origin of the medial patellofemoral ligament.

Medial and Lateral Patellar Retinacula: Swollen but intact medial patellar retinaculum.

Unremarkable lateral patellar retinaculum.

Hoffa’s Fat Pad: Swollen edematous infrapatellar plica.
Articulations:

Patellofemoral Compartment: No patella alta, Baja, trochlear dysplasia or patellar dysplasia. No patella lateralization/subluxation. No intermediate or high-grade chondromalacia. No traumatic osteochondral injury.

Medial Compartment: Subcortical osteoedema of the medial femoral condyle, likely representing stress related osteoedema associated with the MCL and MPFL injuries.

Lateral Compartment: Pivot-shift pattern of osseous injury with minimally depressed sulcus terminalis and subchondral fracture with osteoedema of the lateral femoral condyle and a posterolateral tibial plateau microtrabecular fracture with osteoedema.
General:

Bones: Pivot-shift pattern of osseous injury as described above. Open growth plates. Incidental wide dysplastic intercondylar notch.

Effusion: Moderate-sized suprapatellar effusion/hemarthrosis.

Baker’s Cyst: None.

Loose Bodies: None.

Soft tissue: Unremarkable. Preserved neurovascular bundle.
Conclusion
Pivot-shift mechanism injury with the following:

1.Complete ACL transection.
2.Ramp lesion posterior horn medial meniscus (ramp 1). Slightly prolapsed posterior horn indicative of a “break stop mechanism” injury.
3.Delicate Wrisberg rip tear, measuring approximately 1 cm in length.
4.Intermediate-grade MCL sprain with partial tear of the anterior fibers. Tear extends to involve the femoral origin of the MPFL. Medial meniscofemoral ligament disruption anteriorly.
5.Pivot-shift pattern of osseous injury with minimally depressed sulcus terminalis and microtrabecular posterolateral tibial plateau fracture. Stress related osteoedema medial femoral condyle, in keeping with valgus moment MCL/MPFL injury.
6.Low-grade sprain posterolateral corner without frank disruption. No evidence for posterolateral corner instability.

Case Discussion

Faculty

Omer Awan, MD, MPH, CIIP

Associate Professor of Radiology

University of Maryland School of Medicine

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

Jenny T Bencardino, MD

Vice-Chair, Academic Affairs Department of Radiology

Montefiore Radiology

Edward Smitaman, MD

Clinical Associate Professor

University of California San Diego

Tags

Musculoskeletal (MSK)

MRI

Knee

© 2024 Medality. All Rights Reserved.

Contact UsTerms of UsePrivacy Policy