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A pop in the knee on landing
A 20-year-old basketball player lands from a jump, her knee buckles inward, and she hears a pop. She can't continue, and the knee is swollen within two hours.
Step 1 of 4
Which structure is most likely torn?
Correct answer: D
A non-contact pivot or landing near extension in valgus, a pop and rapid hemarthrosis within hours is an ACL tear (see cruciate ligaments). A PCL tear follows a dashboard injury to the flexed knee.
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D
A non-contact pivot or landing near extension in valgus, a pop and rapid hemarthrosis within hours is an ACL tear (see cruciate ligaments). A PCL tear follows a dashboard injury to the flexed knee.
Step 2 of 4
Which examination test is the most sensitive for this injury?
Correct answer: D
The Lachman test is the most sensitive for an ACL tear; the anterior drawer and pivot-shift tests also help. McMurray tests the menisci; valgus stress at 30° tests the MCL.
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D
The Lachman test is the most sensitive for an ACL tear; the anterior drawer and pivot-shift tests also help. McMurray tests the menisci; valgus stress at 30° tests the MCL.
Step 3 of 4
Which test confirms the diagnosis?
Correct answer: A
MRI confirms the tear and shows associated meniscal and ligament injuries. Young active patients usually have ACL reconstruction.
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A
MRI confirms the tear and shows associated meniscal and ligament injuries. Young active patients usually have ACL reconstruction.
Step 4 of 4
She also has medial joint-line pain and laxity on valgus stress at 30° of flexion.
Which combination makes up the "unhappy triad"?
Correct answer: C
A valgus force can tear the ACL, MCL and medial meniscus together. The medial meniscus is torn more often than the lateral because it is attached to the MCL (see menisci of the knee and collateral ligaments of the knee).
Show answer
C
A valgus force can tear the ACL, MCL and medial meniscus together. The medial meniscus is torn more often than the lateral because it is attached to the MCL (see menisci of the knee and collateral ligaments of the knee).
Key points
- Non-contact pivot + pop + rapid swelling → ACL; Lachman is the most sensitive test.
- Unhappy triad: ACL + MCL + medial meniscus.
Study: Cruciate ligaments, Collateral ligaments of the knee, Menisci of the knee, Knee joint