The 'unhappy triad' of the knee (O'Donoghue triad), typically seen in a valgus twisting injury, consists of injury to:

• A ACL, MCL, and lateral meniscus
• B PCL, LCL, and lateral meniscus
• C ACL, PCL, and medial meniscus
• D ACL, MCL, and medial meniscus ✓

Explanation

The O'Donoghue unhappy triad classically involves the anterior cruciate ligament, medial collateral ligament, and medial meniscus — all injured by a valgus external rotation force on the knee (common in contact sports). Modern MRI studies show that lateral meniscus tears may be equally or more common in acute ACL injuries, but the traditional examination-based teaching remains ACL + MCL + medial meniscus. MCL injuries are treated conservatively; ACL and meniscus injuries require arthroscopic surgical management.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.