An unhappy triad injury is very common in sports like football, where the knees are highly susceptible to external injuries. This is a serious knee injury, which can be quite painful and make walking difficult. The individual may have to be confined to the bed till recovery.

A torn ligament in the knee could be one of the causes of knee pain. However, when three structures of the knee, ACL (anterior cruciate ligament), MCL (medial collateral ligament), and medial meniscus get affected by an external injury, the term coined for such a condition is unhappy triad injury.

Unhappy Triad Knee Injury
It is an aggregation of three types of knee injuries that are explained below. Since this injury involves a meniscus tear, an ACL tear, and an MCL tear, the name unhappy triad is given to it.

ACL Tear: The anterior cruciate ligament tear is very painful and the most crucial of all knee injuries. This ligament helps in balancing of the legs. When there is an ACL tear, the person might experience a knee pain and inability to walk properly (occasionally buckling away).

Meniscus Tear: The meniscus tear involves tearing of the fibrocartilage in the knee joint, thereby reducing the resistance of the knees (since meniscus aids in cushioning the knee bone and reducing friction in bones). A medial meniscus tear can cause inflammation in the knee, triggering pain. Some popping sensations can also be felt in the knee.

MCL Tear: The unhappy triad is completed by the tear of the medial collateral ligament which runs along the inside of the knee. This ligament is responsible for providing stability to the knee joint. Symptoms of pain, decreased range of motion, and instability indicate an MCL tear.

Causes
The injury is an outcome of stressful and rigorous sports activities like football and rugby. When a blow is inflicted on the outside of the knee of an athlete (who is in stance position with feet on ground), chances of this injury are maximum. The ACL tear and meniscus tear can occur simultaneously during a plant and turn movement in a game, When the knee, after the first injury, continues to move along the same path, the ACL tears further causing the knee to shift. Consequently, the femur and tibia compress against the meniscus causing the soft fibrocartilage to tear. And an external blow on the same spot adds to the MCL tear.

Prominent symptoms felt post-injury are swelling in the knee with a bruise around it, severe pain, instability (this happens as tibia and femur slide against each other), and rupture in the triad ligaments.

Treatment
The most painful part of this injury is the ACL tear. It can be treated only with surgery. A person having experienced this injury can take even months to recuperate completely. Reconstructing the ACL is the primary goal in the surgery, after which, the MCL tear and meniscus tear gradually start to heal. Recovery time can range between 6 - 9 months, depending on the seriousness of the injury. Post surgery, knee braces can be used for prophylactic reasons. Many athletes use knee braces for running. This reduces the probabilities of occurrence of this injury.