A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 23-year-old male presents to his primary care physician after an injury during a rugby game. The patient states that he was tackled and ever since then has had pain in his knee. The patient has tried NSAIDs and ice to no avail. The patient has no past medical history and is currently taking a multivitamin, fish oil, and a whey protein supplement. On physical exam you note a knee that is heavily bruised. It is painful for the patient to bear weight on the knee, and passive motion of the knee elicits some pain. There is laxity at the knee to varus stress. The patient is wondering when he can return to athletics. Which of the following is the most likely diagnosis?
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A
Medial collateral ligament tearIncorrect. MCL tears produce VALGUS laxity (opening on the medial side), not varus laxity.
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B
Lateral collateral ligament tearCorrect. varus stress laxity tests the LCL; injury to the LCL is from medial-directed force or contact tackles that bow the knee outward.
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C
Anterior cruciate ligament tearIncorrect. ACL tears produce positive anterior drawer/Lachman and a tense hemarthrosis with a popping sensation — varus laxity is not typical.
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D
Posterior cruciate ligament tearIncorrect. PCL tears cause posterior tibial translation (posterior drawer, sag sign), usually from dashboard injuries.
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E
Meniscal tearIncorrect. Meniscal tears cause joint line tenderness and locking with a positive McMurray sign — not the ligamentous laxity tested by varus stress, which specifically isolates the LCL.
↑ Tap an answer to reveal the reasoning
Answer: B. An athlete with a knee injury sustained from a lateral tackle who has laxity to VARUS STRESS testing has injured the LATERAL collateral ligament (LCL). The LCL resists varus (lateral angulation, knee bowing outward) stress — when the examiner pushes the knee medially with the leg held, abnormal opening on the lateral side indicates LCL injury.
Varus stress is applied with the knee in slight flexion to isolate the LCL from the posterolateral corner. The LCL connects the lateral femoral epicondyle to the fibular head. Direct medial-to-lateral blows ("clipping") or contact injuries that force the knee into varus can tear it. LCL injuries are less common than MCL injuries and are often associated with posterolateral corner injuries — a missed diagnosis that leads to chronic instability.
MCL tears cause VALGUS laxity (opening on the medial side with lateral-to-medial force). ACL tears produce a positive anterior drawer and Lachman test, often with effusion and a popping sensation followed by hemarthrosis. PCL tears produce posterior tibial translation (posterior sag, positive posterior drawer) — typical of dashboard injuries. The varus laxity in this vignette points directly to the LCL.
**Why each option:**
**A.** MCL tears produce VALGUS laxity (opening on the medial side), not varus laxity.
**B.** Correct — varus stress laxity tests the LCL; injury to the LCL is from medial-directed force or contact tackles that bow the knee outward.
**C.** ACL tears produce positive anterior drawer/Lachman and a tense hemarthrosis with a popping sensation — varus laxity is not typical.
**D.** PCL tears cause posterior tibial translation (posterior drawer, sag sign), usually from dashboard injuries.