A cutting guide for resecting a patients proximal tibia to receive a tibial prosthesis is disclosed. The cutting guide comprises an instrument body (76) and mounting means for attaching the cutting guide to a rod (21) that tracks the patients intramedullary canal (12) which enables the surgeon to reference surgical cuts with respect to the patients intramedullary canal. The cutting guide also comprises a cutting element (78) for being driven longitudinally into the proximal tibia during use, and at least one cutting guide surface (90, 91) for guiding a saw instrument of the surgeon.
