0:00

So, this is a 20-year-old man with lateral patellar

0:05

dislocation relocation injury.

0:08

And as we see here,

0:10

the patella is actually still sub-locks

0:13

out of the femoral trochlea.

0:15

There is lateral translation of the patella

0:18

with respect to the central aspect of the trochlea.

0:22

The trochlea smileyis plastic.

0:24

We can see the flattening of the lateral

0:28

femoral trochlear facet,

0:30

relatively short medial trochlear facet.

0:34

And then, the dominant finding here is the

0:38

disruption of the Medial Patellofemoral Ligament.

0:42

As we know,

0:43

the Medial Patellofemoral Ligament attaches

0:46

to the medial margin of the patella,

0:49

and at the level of the femur,

0:51

it goes into the adductor tubercle of the

0:55

supracondylar femoral metaphysis.

0:59

I always search for this adductor tendon,

1:03

the adductor magnus tendon,

1:05

and then where it lands,

1:07

that's the adductor tubercle.

1:09

So, I'm expecting to see

1:11

the medial patellofemoral ligament

1:13

coming around to insert at that same level,

1:17

at the level of the adductor tubercle.

1:19

It's very clear in this patient that we have

1:22

fluid signal interposed between the

1:25

medial patellofemoral ligament,

1:27

the medial patellar retinaculum, and the bone.

1:29

So, this is an avulsion of the medial

1:33

patellofemoral ligament from the adductor tubercle.

1:36

Now, when we go to the patellar site,

1:38

things don't look that hot either.

1:40

You can see how these fibers attaching to

1:44

the patella are partially disrupted.

1:46

So, there is a partial detachment of the MPFL.

1:51

Also from the medial patellar facet.

1:55

There is a very large effusion.

1:57

This effusion is complex because

2:00

there are blood clots.

2:03

Those are the lower signal intensity foci

2:06

within the fluid that we're seeing

2:08

is distending the suprapatellar recess,

2:11

those correspond to a hemarthrosis.

2:15

Now, one important finding

2:17

in this sagittal image that I park here

2:20

is that the pattern of marrow contusion

2:24

in the lateral femoral condyle,

2:26

we know we are lateral.

2:27

You see the fibula head here,

2:29

is that the involvement is

2:31

more anterior to what we expect to see with

2:35

injuries of the anterior cruciate ligament.

2:37

So, the marrow contusion centers

2:40

Wk 4, Case 2 - Review

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0:00

So, this is a 20-year-old man with lateral patellar

0:05

dislocation relocation injury.

0:08

And as we see here,

0:10

the patella is actually still sub-locks

0:13

out of the femoral trochlea.

0:15

There is lateral translation of the patella

0:18

with respect to the central aspect of the trochlea.

0:22

The trochlea smileyis plastic.

0:24

We can see the flattening of the lateral

0:28

femoral trochlear facet,

0:30

relatively short medial trochlear facet.

0:34

And then, the dominant finding here is the

0:38

disruption of the Medial Patellofemoral Ligament.

0:42

As we know,

0:43

the Medial Patellofemoral Ligament attaches

0:46

to the medial margin of the patella,

0:49

and at the level of the femur,

0:51

it goes into the adductor tubercle of the

0:55

supracondylar femoral metaphysis.

0:59

I always search for this adductor tendon,

1:03

the adductor magnus tendon,

1:05

and then where it lands,

1:07

that's the adductor tubercle.

1:09

So, I'm expecting to see

1:11

the medial patellofemoral ligament

1:13

coming around to insert at that same level,

1:17

at the level of the adductor tubercle.

1:19

It's very clear in this patient that we have

1:22

fluid signal interposed between the

1:25

medial patellofemoral ligament,

1:27

the medial patellar retinaculum, and the bone.

1:29

So, this is an avulsion of the medial

1:33

patellofemoral ligament from the adductor tubercle.

1:36

Now, when we go to the patellar site,

1:38

things don't look that hot either.

1:40

You can see how these fibers attaching to

1:44

the patella are partially disrupted.

1:46

So, there is a partial detachment of the MPFL.

1:51

Also from the medial patellar facet.

1:55

There is a very large effusion.

1:57

This effusion is complex because

2:00

there are blood clots.

2:03

Those are the lower signal intensity foci

2:06

within the fluid that we're seeing

2:08

is distending the suprapatellar recess,

2:11

those correspond to a hemarthrosis.

2:15

Now, one important finding

2:17

in this sagittal image that I park here

2:20

is that the pattern of marrow contusion

2:24

in the lateral femoral condyle,

2:26

we know we are lateral.

2:27

You see the fibula head here,

2:29

is that the involvement is

2:31

more anterior to what we expect to see with

2:35

injuries of the anterior cruciate ligament.

2:37

So, the marrow contusion centers

2:40

more in the anterior aspect

2:42

of the lateral femoral condyle,

2:44

and that's because the patella is heading out

2:47

of the femoral trochlea,

2:49

and when it recoils,

2:50

it hits that lateral femoral condyle

2:53

in its anterior portion.

2:55

Very often,

2:56

these patients have a valgus injury.

2:59

So, we see an injury to the medial collateral ligament,

3:03

as in this case,

3:05

with edema overlying the fibers,

3:08

in keeping with a grade one sprain.

Report

Patient History
20-year-old male with right knee pain and swelling 1 week after dislocation.

Findings
Menisci:

Medial Meniscus: Tiny undersurface flap tear posterior horn-body junction.

Lateral Meniscus: Intact. Meniscal flounce adjacent to the inner edge of the meniscal body.

Ligaments:

Anterior Cruciate Ligament: Intact.

Posterior Cruciate Ligament: Intact.

Medial Collateral Ligament: Thickened tibial collateral ligament with increased intrasubstance signal involving the proximal and mid portions with diffuse periligamentous edema, consistent with an low to intermediate grade sprain. Partial-thickness tear of the anterior tibial collateral ligament fibers adjacent to the femoral origin of the medial patellofemoral ligament. Diffusely swollen lax meniscofemoral and meniscotibial ligaments consistent with sprains.

Lateral Collateral Ligament: Intact.

Posterolateral Corner Structures: Intact.

Posteromedial Corner Structures: Intact.

Extensor Mechanism:

Patellar Tendon: Intact.

Distal Quadriceps Tendon: Intact.

Medial Patellofemoral Ligament: Massive tear with rupture of the medial patellofemoral ligament. Avulsion of the distal patella attachment with associated small cortical avulsion fracture. Avulsed proximal femoral attachment with a large gap between the femoral attachment footplate/adductor tubercle and the avulsed medial patellofemoral ligament fragment (at least 5.1 cm gap).

Medial and Lateral Patellar Retinacula: Diffusely torn medial markedly lax patellar retinaculum. Thickened lateral patellar retinaculum.

Hoffa’s Fat Pad: Diffusely contused Hoffa’s fat pad with increased signal.

Articulations:

Patellofemoral Compartment: Moderate to marked laterally subluxed patella. Small cortical avulsion fracture of the medial patella, in the region of the usual medial patellofemoral ligament attachment. Trochlear dysplasia with medial facet hypoplasia and insufficient trochlear groove (Dejour type C). Wiberg 2 patella. Increased TT-TG distance measuring 2.0 cm. Patella alta with Insall-Salvati ratio 2.0 cm. No traumatic chondral or osteochondral lesion.

Medial Compartment: Unremarkable.

Lateral Compartment: Unremarkable.

General:

Bones: Lateral femoral condyle kissing contusion with diffuse marrow edema.

Effusion: Massive hemarthrosis with heterogeneous intermediate to low signal organizing hematoma.

Baker’s Cyst: Moderate amount of fluid tracking along myofascial planes deep to the medial head of the gastrocnemius and superficial to the popliteus muscle belly, which could represent recent dehisced/ruptured Baker’s cyst or myofascial injury.

Loose Bodies: None.

Other, soft tissue and Neurovascular: Diffusely increased signal with fiber discontinuity involving the distal sartorius tendon and myotendinous junction, consistent with intermediate grade strain and partial-thickness tear.

Conclusion
Recent transient patellar dislocation-relocation event with the following:

1.Patellar remains moderately laterally subluxed.
2.Massive rupture medial patellofemoral ligament and medial retinaculum.
3.Avulsion fracture medial patella at the MPFL footplate with corresponding bony kissing contusion of the lateral femoral condyle.
4.Concomitant large hemarthrosis with organizing hematoma.
5.Background of high grade trochlear dysplasia (Dejour C), patella alta and increased TT-TG distance of 2.0cm.
6.Intermediate grade strain with partial distal sartorius tendon tear.
7.Low to intermediate grade (grade I-II) MCL sprain (involving layer II tibial collateral ligament, and layer I meniscofemoral and coronary/meniscotibial ligaments).

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

Practice Cases

Worklist 1

Practice Cases

Worklist 2

Practice Cases

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Practice Cases

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Practice Cases

Worklist 5

Wk 4, Case 2 - Review