In the context of the unhappy triad injury, which two structures are commonly affected along with the anterior cruciate ligament?

• A. Patellar tendon and quadriceps tendon
• B. Posterior cruciate ligament and lateral collateral ligament
• C. Lateral meniscus and tibial plateau
• D. Medial collateral ligament and medial meniscus

Answer: (D)

The unhappy triad injury is a common pattern resulting from a significant force applied to the knee, often during sports-related activities. This injury typically involves the anterior cruciate ligament (ACL), the medial collateral ligament (MCL), and the medial meniscus. The combination of these three structures being affected results from the valgus force that damages the knee when it is in a flexed position, usually accompanied by a rotational component.

In this context, the medial collateral ligament provides stability on the inner side of the knee, while the medial meniscus acts as a shock absorber and helps distribute weight across the knee joint. The concurrent injury to these structures, along with the ACL, leads to significant knee instability and dysfunction.

The other options do not align with the common presentation of the unhappy triad. For instance, the patellar tendon and quadriceps tendon are crucial for knee extension but are not typically part of this injury pattern. Likewise, injuries involving the posterior cruciate ligament and lateral collateral ligament, or the lateral meniscus and tibial plateau, do not represent the classic triad associated with this specific mechanism of injury. Thus, the correct identification of the medial collateral ligament and medial meniscus in conjunction with the ACL highlights the classic components of the unhappy tri