the illustrative embodiment of the invention have a 15 mm diameter boss but different baseplates have bosses with different lengths having chosen the appropriately sized template 84 the practitioner will know which tibial baseplate will be used in the implant and will know how deep to ream the hole for the boss of the baseplate thus at this stage of the method of the invention the practitioner uses the reamer 110 to ream to the appropriate depth indicated by the appropriate depth mark 112 or 114 after reaming for the baseplate boss the tibia is punched to make space for the baseplate fins or 34 keel 34 the boss reamer 110 the neutral bushing 106 and the offset positioning guide 88 are removed and the template 84 is left pinned to the tibia the fin punch guide 120 shown in fig1 is attached to the template 84 the guide 120 has left and right fin guides 122 124 and a central boss guide 126 the fin punch 130 has left and right fins 132 134 and a central boss 136 the punch 130 is inserted into the punch guide 120 as shown in fig1 with the central boss 136 entering the central boss guide 126 and the left and right fins 132 134 entering the left and right fin guides 122 124 with the punch 130 in place it is struck with a mallet or attached to the impactor extractor driven into the tibial plateau and then removed optionally if a wedge cut had not been performed at.