Explanation:
The correct option is b. The mechanical axis of the entire lower limb, which dictates weight-bearing load distribution, is defined as a straight line drawn from the center of rotation of the femoral head directly to the center of the ankle joint (the talar dome). In a normal, neutrally aligned knee, this mechanical axis line passes precisely through the center of the knee joint. In a traditional measured-resection TKA, the primary goal is to cut the bones perpendicularly to their respective mechanical axes to restore a neutral overall limb axis, aiming for symmetrical load distribution across the polyethylene bearing to maximize survivorship. Reference: Insall & Scott Surgery of the Knee.