Which mechanism is a common non-contact cause of ACL injuries in sports?

• A. Direct blow to the knee from the side
• B. Sudden deceleration with rotation
• C. Non-contact pivoting with valgus collapse
• D. Hyperflexion during landing

Answer: (C)

The mechanism being tested is the non-contact, multiplanar knee load that tears the ACL during a pivot. When an athlete plants the foot and pivots, the knee often collapses inward into valgus while the tibia rotates. This combination of valgus stress, rotational torque, and a near-extended knee creates anterior shear and rotatory forces on the ACL that exceed its capacity, even without a direct hit. That blend of forces is the classic non-contact scenario for ACL rupture in many sports.

Direct blows to the knee are contact injuries, not non-contact. Sudden deceleration with rotation can contribute to ACL strain, but the hallmark non-contact pattern that most reliably leads to ACL rupture is pivoting with valgus collapse. Hyperflexion during landing can injure the ACL as well, but the pivot-with-valgus mechanism is the most characteristic non-contact cause.