American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a typical mechanism of injury for an anterior cruciate ligament tear?

1. Direct blow to the knee

2. Rapid deceleration and pivoting

3. Excessive extension of the knee

4. Landing from a jump

The correct answer is: Rapid deceleration and pivoting

A typical mechanism of injury for an anterior cruciate ligament (ACL) tear is rapid deceleration combined with pivoting. This occurs frequently in sports that require sudden changes in direction, such as basketball, soccer, or skiing. When an athlete rapidly slows down and then pivots on a planted foot, the forces exerted on the knee can lead to an ACL tear. During this movement, the instability created by the abrupt direction change puts excessive strain on the ligament. The ACL is crucial for providing stability to the knee joint during these activities, so when it is compromised by this type of force, it can tear. This mechanism is well-documented and is characterized by the "pop" sensation that many athletes report at the moment of injury, often followed by swelling and loss of mobility in the joint. Other mechanisms, while they can cause knee injuries, are less specific for an ACL tear. For example, a direct blow to the knee may cause collateral ligament injuries rather than an ACL tear. Similarly, although excessive knee extension and landing from a jump can lead to injuries around the knee, these actions do not specifically target the ACL in the same way that rapid deceleration and pivoting do. Thus, the predominant mechanism associated with ACL tears remains rapid