Final answer:
A lateral collateral ligament (LCL) injury is caused by a forceful blow to the lateral side of the extended knee, resulting in stretching or damage to the tibial collateral ligament. More severe blows may also lead to tearing of the LCL, as well as damage to the medial meniscus and anterior cruciate ligament (ACL). This combination of injuries is known as a 'terrible triad' injury.
Step-by-step explanation:
A lateral collateral ligament (LCL) injury is caused by a forceful blow to the lateral side of the extended knee. When this happens, the medial side of the joint opens, resulting in stretching or damage to the tibial collateral ligament. In more severe cases, a stronger blow can lead to tearing of the LCL, as well as damage to the medial meniscus and anterior cruciate ligament (ACL). This combination of injuries is known as a 'terrible triad' injury.