Explain the concept of gap balancing versus the measured resection technique in knee arthroplasty.

• A. Gap balancing uses bone landmarks; measured resection uses soft tissue tension.
• B. They are identical.
• C. Gap balancing uses soft-tissue tension to balance flexion/extension gaps; measured resection uses bone landmarks to align cuts and then balance ligaments.
• D. Gap balancing uses only implants.

Answer: (C)

In knee replacement, you can balance the knee either by guiding the procedure with soft-tissue tension or by precisely following bone landmarks. Gap balancing centers on achieving equal flexion and extension gaps by managing the soft tissues first. The surgeon uses a tensor or spacer to assess how tight or loose the collateral ligaments and surrounding structures are, then adjusts the balance by soft-tissue releases or resections until the flexion and extension gaps are symmetric. The bone cuts are then made to maintain that balanced, tensioned state, so the final alignment reflects the achieved soft-tissue balance.

Measured resection, on the other hand, starts with bone-cut plan defined by anatomical landmarks. The surgeon references predefined landmarks on the bones to determine where to cut, aiming to recreate the native shape and alignment of the knee. After these cuts, the ligaments are balanced, and any necessary releases are performed to obtain even gaps. Here, the primary guide is the bone anatomy, with soft-tissue balancing following the bone cuts.

So the key difference is whether soft-tissue tension guides the balance first (gap balancing) or bone landmarks guide the bone cuts first (measured resection), with soft-tissue balancing then adjusted as needed in the latter.