Definition: The "Unhappy Triad" is an injury to the knee. The unhappy triad injury commonly occurs in contact sports such as football when the knee is hit from the outside. This causes an injury to three knee structures: the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and the medial meniscus.
Unhappy Triad
By Jonathan Cluett, M.D., About.com
About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD
Unhappy Triad Injuries
Anterior Cruciate Ligament InjuryMedial Collateral Ligament InjuryMeniscus Tear
Sports Injuries
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