A customized patient-specific orthopaedic surgical instrument includes a customized patient-specific tibial pin guide (100). The guide includes a body (102) having a bone-facing surface (112) that has a customized patient-specific negative contour configured to receive a portion of an anterior side of a patients tibia that has a corresponding positive contour. The body has a first hole (116) formed therein with a first locking slot (126) extending in a direction parallel to the axis of the first hole, and opening into the first hole. The body also has a second hole (116) formed therein with a second locking slot (126) extending in a direction parallel to the axis of the second hole, and opening into the second hole. The guide also has a first tab (104) and a second tab (106) extending posteriorly from the body, the first tab and the second tab each including a bone-facing surface that has a customized patient-specific negative contour configured to receive a portion of the proximal side of the patients tibia that has a corresponding positive contour. The instrument includes a first removable drill bushing (118) having a post (122) with a locking flange (124) extending therefrom, which is positioned in the first hole of the body of the guide such that the locking flange of the first removable drill bushing is positioned in the first locking slot of the body of the guide. The instrument further includes a second removable drill bushing (118) having a post (122) with a locking flange (124) extending therefrom, which is positioned in the second hole of the body of the guide such that the locking flange of the second removable drill bushing is positioned in the second locking slot of the body of the guide.
