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Old 04-03-2011
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Arrow High Yield Question #6

Which of the fallowing structure is indicated by letter A? MRI of the right leg.

High Yield Question #6-md_03-01-0067.jpg
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A) Anterior cruciate ligament
B) Posterior cruciate ligament
C) Lateral lemniscus
D) Medial lemniscus
E) Quadriceps tendon
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A) Anterior cruciate ligament
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A) Anterior cruciate ligament
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Anterior Crucitae Ligament
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A) Anterior cruciate ligament
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Correct ans is A) Anterior cruciate ligament

normal patellar tendon (p)
quadriceps tendon (q)

The anterior cruciate ligament (ACL)
The posterior cruciate ligament (PCL)
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MRI of the knee: coronal section



1, Vastus medialis muscle.
2, Femur.
3, Vastus lateralis muscle.
4, Posterior cruciate ligament.
5, Anterior cruciate ligament.
6, Tibial collateral ligament.
7, Fibular collateral ligament.
8, Medial meniscus.
9, Lateral meniscus.
10, Tibia.
11, Fibula.
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A) Anterior Cruciate Ligament: attaches anteriorly on the tibia and courses posteriorly to attach on the posterior aspect of the distal femur --> Prevents anterior dislocation
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Quote:
Originally Posted by apx85 View Post
A) Anterior Cruciate Ligament: attaches anteriorly on the tibia and courses posteriorly to attach on the posterior aspect of the distal femur --> Prevents anterior dislocation
That is correct.

Posterior cruciate ligament prevents posterior dislocation.
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Also, remember that with a when your knee is subject to a strong lateral force, such as in a football injury, the three structures most often damaged are the MCL, ACL, and Lateral meniscus. This is because the tibia internally rotates and therefore the lateral meniscus rubs up against the lateral condyle of the femur and has a tendency to tear.
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Quote:
Originally Posted by aktorque View Post
MRI of the knee: coronal section



1, Vastus medialis muscle.
2, Femur.
3, Vastus lateralis muscle.
4, Posterior cruciate ligament.
5, Anterior cruciate ligament.
6, Tibial collateral ligament.
7, Fibular collateral ligament.
8, Medial meniscus.
9, Lateral meniscus.
10, Tibia.
11, Fibula.
Thanks for this excellent post

How would you differentiate between posterior cruciate and anterior cruciate on this MRI? Is the posterior one always the one that appears medially from the back?
Also, are vastus medialis and vastus lateralis always the most posterior muscles on this kinda image?
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Quote:
Originally Posted by apx85 View Post
Also, remember that with a when your knee is subject to a strong lateral force, such as in a football injury, the three structures most often damaged are the MCL, ACL, and Lateral meniscus. This is because the tibia internally rotates and therefore the lateral meniscus rubs up against the lateral condyle of the femur and has a tendency to tear.
I thought it is the MCL, ACL and the Medial Miniscus?
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Quote:
Originally Posted by riya99 View Post
Thanks for this excellent post

How would you differentiate between posterior cruciate and anterior cruciate on this MRI? Is the posterior one always the one that appears medially from the back?
Also, are vastus medialis and vastus lateralis always the most posterior muscles on this kinda image?
Read on this following site

http://books.google.ca/books?id=rmm6...page&q&f=false

http://books.google.ca/books?id=NK9T...aments&f=false
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Quote:
Originally Posted by riya99 View Post
I thought it is the MCL, ACL and the Medial Miniscus?
This is a common mistake and thus it could very well show up on our test. The meniscus that is most likely damaged is the LATERAL meniscus, not the medial (for the reason I specified above). Check FA 2011 page 370 under MSK
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Quote:
Originally Posted by apx85 View Post
This is a common mistake and thus it could very well show up on our test. The meniscus that is most likely damaged is the LATERAL meniscus, not the medial (for the reason I specified above). Check FA 2011 page 370 under MSK
Injury to the medial meniscus is above 5 times more common than injury to the lateral meniscus in lateral side of the knee injuries.

http://books.google.ca/books?id=BjWq...injury&f=false
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Quote:
Originally Posted by apx85 View Post
Also, remember that with a when your knee is subject to a strong lateral force, such as in a football injury, the three structures most often damaged are the MCL, ACL, and Lateral meniscus. This is because the tibia internally rotates and therefore the lateral meniscus rubs up against the lateral condyle of the femur and has a tendency to tear.
You found a FA errata! According to Netter's Clinical Anatomy, the "Unhappy triad" of O'Donoghue is rupture of
1. medial collateral ligament
2. medial meniscus
3. anterior cruciate ligaments


This makes sense, because the medial meniscus is attached to the MCL, so they are often injured together. The LCL is mobile and not attached to the lateral meniscus, so these these are less likely to be injured.

(Ps. You can also find this info on page 299 of Kaplan Anatomy LN, the green one).

To see a nice pic of this, click http://www.netterimages.com/image/12416.htm

Last edited by heights; 04-03-2011 at 04:24 PM. Reason: Added image link
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never mind
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Actually, apx85 may be correct...here's some more info on this

- The "classic unhappy triad" (O’Donoghue’s triad) due to an acute valgus stress on the knee involves the ACL, MCL, and medial meniscus.
- However, recent studies suggest two things:
1. The triad of ACL, MCL and lateral meniscus injury is actually more common than the classic triad following acute valgus stress on the knee
2. In patients that do develop the classic unhappy triad , only the ACL and MCL are acutely injured during the acute valgus stress on the knee, while the injury to the medial meniscus is the result of chronic injury secondary to ACL insufficiency [3]
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Quote:
Originally Posted by heights View Post
Actually, apx85 may be correct...here's some more info on this

- The "classic unhappy triad" (O’Donoghue’s triad) due to an acute valgus stress on the knee involves the ACL, MCL, and medial meniscus.
- However, recent studies suggest two things:
1. The triad of ACL, MCL and lateral meniscus injury is actually more common than the classic triad following acute valgus stress on the knee
2. In patients that do develop the classic unhappy triad , only the ACL and MCL are acutely injured during the acute valgus stress on the knee, while the injury to the medial meniscus is the result of chronic injury secondary to ACL insufficiency [3]
That is absolutely correct heights. Acutely, Lateral meniscus tear is likely. Chronically, medial meniscus tear is likely.

We are in our MSK block and I talked to a resident and a fellow about this topic and they said that medial meniscus tears occur later because of instability of the knee joint. The resident actually had an ACL tear which he did not get repaired so he said that he is almost inevitably going to get a Medial meniscus tear at some point because of joint instability.

But for the acute injury of athlete's triad, we should be concerned about a lateral meniscus tear. Like you said heights, this is a relatively new finding but could very well be tested on our exam.
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Also, on the Netter image that heights posted, notice that the medial meniscus and medical condyle are far away from each other while the lateral meniscus and lateral condyle are rubbing against each other, thus likely to lead to a tear.

It might be confusing because the MCL is connected to the medial meniscus, but somehow this is generally not affected.

Hope that helps
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@aktorque Thanks for the questions & images !!!!!

About the unhappy triad,

this has been discussed in this thread

http://www.usmle-forums.com/usmle-st...jan-vs-fa.html.
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Quote:
Originally Posted by aktorque View Post
Which of the fallowing structure is indicated by letter A? MRI of the right leg.

Attachment 1220
click image to enlarge

A) Anterior cruciate ligament
B) Posterior cruciate ligament
C) Lateral lemniscus
D) Medial lemniscus
E) Quadriceps tendon
Im having trouble understanding how we are looking at the MRI here...is it a side view or from the front of the leg?

like isnt that the patella on the left up there ?? lol like displaced??
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Quote:
Originally Posted by Cautie Pie View Post
Im having trouble understanding how we are looking at the MRI here...is it a side view or from the front of the leg?

like isnt that the patella on the left up there ?? lol like displaced??
The first one's from the side, the second one's from the front...
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Quote:
Originally Posted by Mondoshawan View Post
The first one's from the side, the second one's from the front...
ohh okay so the first one is from the side!
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