<human>:  What is the difference between an ACL and a PCL tear?
<bot>: The difference between an ACL (Anterior Cruciate Ligament) tear and a PCL (Posterior Cruciate Ligament) tear is that an ACL tear is a tear to the ligament in the knee joint located in the front of the knee, while a PCL tear is a tear to the ligament located in the back of the knee. An ACL tear is usually caused by a sudden change in direction or a hard hit, while a PCL tear is usually caused by an impact that causes the knee to bend too far backward. Both types of tears can cause severe knee instability and may require surgery to repair.