Which of the following is NOT a part of the 'unhappy triad'?

The structure commonly referred to as the "unhappy triad" typically consists of three specific injuries that occur simultaneously during a trauma to the knee, most often during sports activities such as contact sports or when an athlete suddenly pivots or changes direction. The injuries that make up this triad include a full tear of the anterior cruciate ligament (ACL), a tear of the medial collateral ligament (MCL), and a tear to the medial meniscus.

The presence of partial tears of the PCL does not fit into this set of injuries. While the posterior cruciate ligament (PCL) can certainly be injured, it is not traditionally included in the definition of the "unhappy triad." Instead, the focus is on the ACL, MCL, and medial meniscus as the primary components that characterize this specific injury pattern, hence making the partial tears of the PCL irrelevant to the triad. Understanding this triad is crucial for treatments and rehabilitation strategies in sports medicine, as these injuries can significantly affect the knee’s stability and functionality.