Abstract

A distal femoral cutting instrument includes an intramedullary rod for referencing the patient's intramedullary canal. A valgus block with a flat reference surface mounts to the intramedullary rod at a bore of the valgus block. The bore of the block has a slant with respect to the flat reference surface on the valgus block. The reference surface defines a line that is normal to the mechanical axis of the patient while the bore of the valgus block tracks the patient's biomechanical axis. A distal femoral cutting block removably attaches to the valgus block and provides a flat cutting guide surface for shaping the patient's distal femur. The valgus block, intramedullary rod, and a stylus (for connecting the valgus block and cutting together) are removed as a unit before shaping of the distal femur. An indexing system includes a gauge having a series of openings corresponding to "anterior" referencing and to "posterior" referencing. During anterior referencing, the gauge allows the surgeon to select the next smaller size prosthesis if the size falls in between available sizes. In posterior referencing, the gauge allows the surgeon to select the next larger size prosthesis if the gauge measures a size that falls in between available sizes.