In knee arthroplasty, what is the typical alignment goal for the postoperative mechanical axis?

• A. 5 degrees varus.
• B. 0 degrees exactly.
• C. Neutral within about ±3 degrees to optimize load distribution and implant longevity.
• D. 5 degrees valgus.

Answer: (C)

Achieving a neutral mechanical axis minimizes uneven loading on the knee prosthesis. When the load line from hip to ankle passes close to the knee center, stress is distributed more evenly across the femoral and tibial components and the polyethylene insert, which helps reduce wear and lowers the risk of aseptic loosening over time. In practice, surgeons aim for neutral alignment within a small tolerance, about ±3 degrees, because this range provides a balance between ideal load distribution and achievable surgical precision. If the axis ends up around 5 degrees varus or 5 degrees valgus, one compartment bears excess load, increasing wear and potentially shortening implant longevity. Hence, the best target is neutral within roughly ±3 degrees.