An orthopaedic surgical instrument system comprising: a first surgical reamer including an elongated shaft and a plurality of cutting flutes defined at a distal end of the elongated shaft , a tibial base plate including a central opening extending along a first longitudinal axis and a pair of fixation bores , an offset guide including an upper drum , a lower plate sized to be positioned in the central opening of the tibial base plate , and a bore extending through the offset guide along a second longitudinal axis that is offset from the first longitudinal axis of the tibial base plate when the offset guide is positioned on the tibial base plate , the bore being sized to receive the elongated shaft of the surgical reamer , and a reamer guide body having a passageway defined therein that is configured to be substantially aligned with the central opening of the tibial base plate when the reamer guide body is positioned on the tibial base plate , and a pair of fixation pins , wherein the offset guide is operable to rotate such that the lower plate of the offset guide engages the tibial base plate to rotate the tibial base plate about the second longitudinal axis; characterized in that : each of the fixation pins extending downwardly from the bottom surface of the guide body and sized to be received in and extend outwardly from each of the fixation bores of the tibial base plate when the guide body is positioned on the tibial base plate ; and wherein the offset guide includes a conical inner surface that defines the bore , the conical inner surface extending from an upper opening to a lower opening smaller than the upper opening . a first surgical reamer including an elongated shaft and a plurality of cutting flutes defined at a distal end of the elongated shaft , a tibial base plate including a central opening extending along a first longitudinal axis and a pair of fixation bores , an offset guide including an upper drum , a lower plate sized to be positioned in the central opening of the tibial base plate , and a bore extending through the offset guide along a second longitudinal axis that is offset from the first longitudinal axis of the tibial base plate when the offset guide is positioned on the tibial base plate , the bore being sized to receive the elongated shaft of the surgical reamer , and a reamer guide body having a passageway defined therein that is configured to be substantially aligned with the central opening of the tibial base plate when the reamer guide body is positioned on the tibial base plate , and a pair of fixation pins , wherein the offset guide is operable to rotate such that the lower plate of the offset guide engages the tibial base plate to rotate the tibial base plate about the second longitudinal axis; characterized in that : each of the fixation pins extending downwardly from the bottom surface of the guide body and sized to be received in and extend outwardly from each of the fixation bores of the tibial base plate when the guide body is positioned on the tibial base plate ; and wherein the offset guide includes a conical inner surface that defines the bore , the conical inner surface extending from an upper opening to a lower opening smaller than the upper opening . each of the fixation pins extending downwardly from the bottom surface of the guide body and sized to be received in and extend outwardly from each of the fixation bores of the tibial base plate when the guide body is positioned on the tibial base plate ; and wherein the offset guide includes a conical inner surface that defines the bore , the conical inner surface extending from an upper opening to a lower opening smaller than the upper opening . <EOS>