Final answer:
The anterior cruciate ligament (ACL) tear is a common injury to the knee, often caused by a forceful blow to the anterior knee or by sudden changes in direction during physical activity.
Step-by-step explanation:
An anterior cruciate ligament (ACL) tear is a common injury to the knee joint. The ACL is an intracapsular ligament of the knee that extends from the anterior, superior surface of the tibia to the inner aspect of the lateral condyle of the femur, helping to resist hyperextension of the knee. Most commonly, ACL injuries occur during activities that involve a forceful blow to the anterior knee, producing hyperextension, or sudden changes in direction that result in twisting and hyperextension of the knee joint.