During midstance, how is knee extension maintained when quadriceps activity is low?

During midstance, how is knee extension maintained when quadriceps activity is low?

• A. Active quadriceps contraction maintains extension.
• B. Hamstrings provide the lock mechanism.
• C. Hip abductors drive knee stabilization.
• D. Passive bone/ligament lock maintains extension.

Answer: (D)

During midstance the knee bears body weight while remaining near full extension. That extension is kept primarily by a passive mechanism—the bone/ligament lock. In a closed-chain situation (foot planted), as the knee approaches extension the femur rotates internally on the tibia, which tightens the knee ligaments and posterior capsule. This increased ligamentous tension and joint congruence create a stable, extended knee with little or no need for active quadriceps contraction. In short, the knee stays extended because the joint’s geometry and ligamental restraints provide passive stability.

During midstance the knee bears body weight while remaining near full extension. That extension is kept primarily by a passive mechanism—the bone/ligament lock. In a closed-chain situation (foot planted), as the knee approaches extension the femur rotates internally on the tibia, which tightens the knee ligaments and posterior capsule. This increased ligamentous tension and joint congruence create a stable, extended knee with little or no need for active quadriceps contraction. In short, the knee stays extended because the joint’s geometry and ligamental restraints provide passive stability.