A cutting guide instrument for use in a cutting step in an orthopedic surgical procedure comprises a reference component comprising a first element which can be attached or otherwise aligned relative to the bone in a predetermined arrangement and a locator arm. The invention further comprises a cutting block comprising a reference surface which can be engaged by a cutting tool to define the location and orientation of the tool during the cutting step. The cutting block further comprises at least one fixation bore for receiving a fixation pin to fix the cutting block to the bone. The locator arm can be fitted against the reference surface so that the reference component and cutting block are arranged in a predetermined manner.
