The instrument has distance blocks and cutting slot blocks arranged on a carrier and retaining geometrical characteristics of a sagittal plane of a distal femur shaft even in a level of a pineal gland of a femur. Positions of the cutting slot blocks are changed by the distance blocks and/or sliding guides. Positions of platforms of the distance blocks staying in contact to condyles are in variable alignment relative to a central body of the instrument for following an alignment of the condyles. The platform lies at a point of convexities of the condyles.
