A footballer sustains a valgus blow to the knee with the foot planted and the tibia externally rotated. Arthroscopy confirms two ligament ruptures and a meniscal tear. According to the classical 'unhappy triad' of O'Donoghue, the three structures injured are:

• A Anterior cruciate ligament, posterior cruciate ligament and lateral meniscus
• B Medial collateral ligament, lateral collateral ligament and medial meniscus
• C Anterior cruciate ligament, medial collateral ligament and medial meniscus ✓
• D Anterior cruciate ligament, medial collateral ligament and lateral meniscus

Explanation

The classical O'Donoghue triad consists of ACL rupture, MCL rupture and medial meniscus tear, caused by a valgus force with external tibial rotation on a planted foot. Modern arthroscopic series actually show the lateral meniscus is injured more often with ACL tears, but standard textbook teaching and Indian examinations still expect the medial meniscus as the third component. Option D, which substitutes the lateral meniscus, is the deliberate trap based on this newer literature.

Reference: Apley's System of Orthopaedics and Fractures, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.