Setting the prosthetic knee too far posterior to the TKA line results in what?

• A. Increased knee flexion
• B. Buckling
• C. Reduced stability
• D. Excessive knee stability and difficulty flexing knee

Answer: (D)

Placing the prosthetic knee too far posterior to the TKA line changes how the knee’s stability mechanism engages during movement, making the knee overly stable and harder to bend. When the knee is set back, the posterior structures and the knee’s stability features engage sooner and more firmly as flexion begins, so bending the knee faces extra resistance. That gives a stiff-feeling, overly stable knee and a reduced ability to flex.

This isn’t about getting more bend (that would be increased flexion) or about the knee giving way (buckling). Nor is it about reduced stability—the alignment makes the knee too stable, especially in flexion, leading to difficulty with knee bending.