During anterior cruciate ligament (ACL) injury, the classic valgus-flexion-external rotation mechanism of the knee is associated with the O'Donoghue 'unhappy triad'. Which three structures are injured?
- A ACL, PCL, lateral meniscus
- B ACL, medial collateral ligament (MCL), medial meniscus ✓
- C PCL, MCL, lateral meniscus
- D ACL, LCL, lateral meniscus
Correct answer: B. ACL, medial collateral ligament (MCL), medial meniscus
Explanation
O'Donoghue's unhappy triad (terrible triad) classically involves injury to the ACL, medial collateral ligament (MCL), and medial meniscus. The valgus stress with flexion tears the MCL; the rotational component ruptures the ACL; the medial meniscus, being firmly attached to the MCL via the coronary ligament, is pulled and torn. Modern literature sometimes reports lateral meniscus injury in contact ACL injuries, but the classical examination teaching remains ACL + MCL + medial meniscus.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.