the im canal yet still provide the post portion 56 with a diameter compatible with the cavity 52 in another embodiment the base 58 and the first end 44 further include fluted outer surfaces to enhance contact with the im canal 48 and prevent rotation of the guide rod 40 within the im canal 48 the depth and positioning of the guide rod 40 within the im canal is selected to permit the milling bit 20 to precisely cut the aperture 50 to a desired depth the accuracy of the depth of the aperture 50 is a crucial element of any arthroplasty procedure as such the milling device 10 further comprises means for accurately determining the depth of the aperture 50 for example in one embodiment the outer surface of the shaft portion 24 comprises a plurality of annular reference marks 68 the reference marks 68 provide a visual indication of the depth of the removable blade 32 relative to various physiological references on the bone being cut in an embodiment where the aperture 50 is being cut into the tibia 14 the required depth of the aperture 50 is either 2 mm below the normal level 70 of the bone 13 mm below the tibial spines 72 or 10 mm below the lateral side 74 thus the reference marks 68 are observed relative to the physiological references 70 72 and 74 to determine the depth of the aperture 50 where the aperture is being cut into another bone such as the femur 16 other.