USMLE® Step 1 style questions USMLE
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A 26-year-old man comes to the office because of severe right knee pain and swelling. The patient currently works as a professional soccer player. His medical history is noncontributory. When asking the patient about his injury, he remembers jumping up to head the ball and colliding with someone in the air to finally land on his right knee. The patient additionally mentions that the pain worsens when he tries to bend his knee and he hears it "click" occasionally. Physical exam shows a "popping sound" on external rotation of his knee, limited knee extension, and tenderness to palpation. His temperature is 36.7°C (97.9°F), pulse is 57/min, respirations are 19/min, blood pressure is 110/60 mmHg. A knee MRI shows a high intrameniscal signal extending to the articular surface. Which of the following is the most likely diagnosis?
Content Reviewers:Yifan Xiao, MD
The menisci are crescent-shaped fibrocartilage cushions found in the knee joint.
This usually occurs due to trauma during contact sports.
The knee is a complex joint, actually it’s a combination of three joints.
Between the femoral and tibial condyles, there’re the medial and lateral menisci.
The menisci act to absorb compressive force, which can reach up to three times the body weight while walking!
In addition, the menisci have a cup-shaped surface which provides a deeper place for the condyles to fit in improving joint’s stability.
Next, the knee joint is supported by a number of ligaments.
So, within the joint space, there's the anterior cruciate ligament, or ACL, which runs from the anterior middle edge of the tibia to the lateral condyle of the femur, and the posterior cruciate ligament, or PCL, that runs from the middle posterior edge of the tibia to the medial condyle of the femur.
Now, outside the joint space, we’ve got one collateral ligament between the femur and the tibia on each side of the joint, which are the lateral collateral ligament, or LCL, and the medial collateral ligament, or MCL.
A meniscus tear can occur when the meniscus is violently compressed, called an acute tear, which usually occurs in young athletes.
Acute tears typically occur when the knee is bent and at the same time excessively twisted, like when you’re playing basketball and then you suddenly change direction, trying to crossover another player.
Acute meniscus tears can also occur as a part of the unhappy triad injury.
This is where a lateral force to the knee, like when the knee is hit by a hockey puck, causes tears in the ACL, MCL and one of the menisci.
Now, regarding which of the menisci, it’s worth mentioning that even though the classic “unhappy triad” consists of the ACL, MCL and medial meniscus tears, the lateral meniscus is more commonly injured than the medial.
This is because when the knee is affected by a blow from the lateral side, the lateral meniscus gets compressed between the tibia and the femur, leading to injury.
In contrast to an acute tear, there are also chronic tears, which usually occur in older people.
This is because the wear and tear of the menisci make them more susceptible to tears with minimal force, or any noticeable trauma.
An elderly person might tear their meniscus from simply getting up from a chair.
Alright, let’s talk about symptoms.