What is a typical mechanism of ACL injuries?

• A. Direct blow to the knee
• B. Hyperextension with axial load
• C. Valgus loading with contact
• D. Non-contact pivoting with sudden deceleration and change of direction

Answer: (D)

The typical mechanism is a non-contact pivoting motion with sudden deceleration and a change of direction. In this scenario, the athlete plants the foot and rapidly twists the knee, generating large anterior tibial shear and rotational forces on the ACL as the body continues to move while the knee is trying to stop. The knee is often near full extension or in slight flexion with a valgus and rotational loading, which places the ACL under peak strain and can lead to tearing even without any direct blow to the knee. This pattern is common in sports that involve cutting, pivoting, and abrupt stops, such as basketball, soccer, and football. While direct impact or hyperextension can injure the ACL, the non-contact pivot-and-deceleration mechanism is the most typical.