What motion during the gait cycle unlocks the knee by causing the femur to rotate laterally?

What motion during the gait cycle unlocks the knee by causing the femur to rotate laterally?

• A. Dorsiflexion of the ankle
• B. Plantarflexion of the foot
• C. Internal rotation of the tibia
• D. Pronation of the subtalar joint

Answer: (D)

Pronation of the subtalar joint is the motion that starts the chain leading to knee unlocking. When the foot pronates during early stance in gait, the subtalar joint everts and the tibia tends to internally rotate. In a closed-chain situation like standing and walking, this tibial internal rotation makes the femur rotate externally (laterally) on the tibia, breaking the screw‑home lock and allowing the knee to flex to absorb shock and continue the gait cycle. The other ankle movements don’t initiate this chain of rotations that results in the femur turning laterally and unlocking the knee.