Understand the most common causes for an unhappy triad injury
Unfortunately the unhappy triad is a very common sports injury, specifically in contact sports like football and even in other sports like soccer and basketball where the knee can often be hit. It is thought to be the most common knee injury in football and occurs when the knee is clipped during a tackle. Normally the unhappy triad occurs when the foot is planted and the knee is hit and pushed in another direction. Normally this happens when the knee is pushed sideways and the feet are planted securely. This forceful lateral motion causes the ligaments and tendons to tear and rip, this causing the terrible or unhappy triad.
The most common thing that happens to cause a unhappy triad starts with the ACL. When the knee is hit or twisted forcefully, the ACL which is rather sensitive, rips and simultaneously the meniscus begins to tear. After this happen, the knee continues to move but is much less stable. This continued movement causes the MCL, located on the inside of the knee, to then tear due to the force. Since the injury causes all three to be torn, it is known as the unhappy triad.