An instrument assembly for resecting a distal femur for receipt of a knee implant, comprising an intramedullary rod and resection instruments. A valgus portion of the intramedullary rod has series of engagement members positioned to provide a plurality of engagement positions for use in fixing the resection instruments on the valgus portion. The resection instruments are configured to selectively engage and selectively lock on the valgus rod at the engagement positions via the engagement members. The engagement members preferably comprise pairs of substantially vertical indents arranged in parallel along opposing sides of said valgus portions. The resection instruments preferably engages and locks to said engagement members via a sliding rod engagement member. The resection instruments preferably include a distal cut guide having a distal resection slot and a femoral resection block.