Which muscle group can produce an anterior tibial shear on the knee but is not a primary stabilizer in PCL deficiency?

• A. Biceps femoris
• B. Popliteus
• C. Quadriceps femoris
• D. Semimembranosus

Answer: (C)

The key idea is that anterior tibial shear is produced by quadriceps contraction. When the quadriceps fire, they pull the tibia forward relative to the femur, especially with the knee flexed, creating forward or anterior shear of the tibia on the femur. In PCL deficiency, the main job of the PCL is to prevent posterior translation of the tibia, so losing it makes the tibia more prone to move backward under load. But the quadriceps are not a primary stabilizer for this posterior restraint; they are knee extensors whose action can increase anterior translation rather than provide posterior stabilization. The other muscles listed tend to pull the tibia posteriorly or act mainly to unlock or control rotation, not to produce anterior tibial shear. So the quadriceps are the group capable of producing anterior tibial shear while not serving as the primary stabilizer in PCL deficiency.