The “Unhappy Triad” is an injury to the knee when three structures in the knee — two ligaments and the meniscus — are injured at the same time.
This injury commonly occurs in contact sports, such as football or rugby, when the knee is hit from the outside while the foot is fixed in place. This multiple injury also is seen in skiers.
The “unhappy triad” occurs when the force of the blow to the leg rotates the leg, causing the medial collateral ligament (MCL) to tear. If the MCL tears, the medial meniscus will likely tear because it is attached to the deep layer of the MCL. The force of the blow then continues to the anterior cruciate ligament (ACL), which also tears.
In cases of combined injuries to the knee, such as those in the “unhappy triad,” surgical repair of the MCL and meniscus at the same time of ACL reconstruction is usually the preferred solution.