Which mechanism is commonly associated with posterior cruciate ligament injuries?

Which mechanism is commonly associated with posterior cruciate ligament injuries?

• A. Hyperflexion
• B. Anterior tibial thrust
• C. Posterior tibial thrust
• D. Valgus stress

Answer: (C)

A posteriorly directed force on the tibia relative to the femur is the mechanism most commonly associated with PCL injuries. The PCL’s job is to prevent the tibia from moving backward beneath the femur, so when the knee is flexed and a force drives the tibia posteriorly—such as a dashboard injury or a fall onto a flexed knee—the PCL bears the brunt and can tear. This mechanism is captured by the idea of posterior tibial thrust, where the tibia is driven backward, producing laxity on posterior displacement tests. In contrast, an anterior tibial thrust stresses the ACL (anterior translation of the tibia), valgus stress implicates medial knee structures (MCL and often other ligaments) rather than the PCL, and hyperflexion is a less specific mechanism for PCL injury. Therefore, posterior tibial thrust best fits the common mechanism for PCL injury.

A posteriorly directed force on the tibia relative to the femur is the mechanism most commonly associated with PCL injuries. The PCL’s job is to prevent the tibia from moving backward beneath the femur, so when the knee is flexed and a force drives the tibia posteriorly—such as a dashboard injury or a fall onto a flexed knee—the PCL bears the brunt and can tear. This mechanism is captured by the idea of posterior tibial thrust, where the tibia is driven backward, producing laxity on posterior displacement tests.

In contrast, an anterior tibial thrust stresses the ACL (anterior translation of the tibia), valgus stress implicates medial knee structures (MCL and often other ligaments) rather than the PCL, and hyperflexion is a less specific mechanism for PCL injury. Therefore, posterior tibial thrust best fits the common mechanism for PCL injury.