What is the purpose of the ACL?

• A. Limits anterior translation of the tibia on the femur and provides rotational stability
• B. Limits posterior translation of the tibia on the femur
• C. Prevents valgus stress at the knee
• D. Stabilizes against varus forces

Answer: (A)

The ACL mainly prevents the tibia from sliding forward relative to the femur and provides rotational stability of the knee. Its fibers run in a way that they tighten when the shin tries to move anteriorly and during internal rotation, helping control pivoting and sudden directional changes. That combination—limiting anterior tibial translation and stabilizing rotation—is why this ligament is key for knee stability. The other statements refer to different ligaments: posterior tibial translation is mainly restrained by the PCL; valgus stress is resisted mainly by the MCL; varus forces are resisted mainly by the LCL and associated structures.