An unhappy triad (or terrible triad, O'Donoghue's triad or a "blown knee") is an injury to the anterior cruciate ligament, medial collateral ligament, and the meniscus. The triad refers to a complete or partial tear of the anterior cruciate ligament, medial collateral ligament, and the meniscus. Originally the "unhappy triad" included the medial meniscus and not the lateral meniscus. However, during the 1990s analysis indicated that 'classic' O'Donoghue triad is actually an unusual clinical entity among athletes with knee injuries. In this type of injury, acute tears of the medial meniscus always present with a concomitant lateral meniscus injury...