An unhappy triad (or terrible triad, "horrible triangle", 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 the '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. However, the lateral meniscus tears are far more common than medial meniscus tears in sprains of the ACL.
In 1936 Cambell stated that an "impairment of the anterior crucial and medial ligaments is associated with injuries of the internal cartilage". In 1950, O'Donoghue described the unhappy triad as: (1) rupture of the medial collateral ligament, (2) damage to the medial meniscus and (3) rupture of the anterior cruciate ligament. O'Donoghue estimated the incidence rate in the traumatic sports knee to be 25%.
Current injury S83.2
In sports and orthopedics, a tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of one of the tibiae. Menisci can be torn during innocuous activities such as walking or squatting. They can also be torn by traumatic force encountered in sports or other forms of physical exertion. The traumatic action is most often a twisting movement at the knee while the leg is bent. In older adults, the meniscus can be damaged following prolonged 'wear and tear' called a degenerative tear.