Presented is a preoperatively designed guidance tool for intraoperative use during bone or joint surgery wherein the guidance tool is specific to the anatomy of the patient being treated. The guidance tool comprises a body portion, a mating surface provided on the body portion for positioning the guidance tool on a corresponding registration surface of a patients anatomy. The guidance tool further comprises at least one guide mechanism provided on the body portion for guiding a medical instrument at one or more preoperatively defined trajectories relative to a patients anatomy. In the event of misalignment, the at least one guide mechanism is adjustable to alter the one or more preoperatively defined trajectories if necessary during intraoperative use. Also presented is a preoperative process for designing the guidance tool.
