A method of intraoperatively selecting between a partial knee arthroplasty and total knee arthroplasty includes mounting a patient-specific three-dimensional surface of a convertible patient-specific guide in a unique position mating to a corresponding surface of a distal femoral bone. The convertible patient-specific guide includes an anterior portion and a distal portion a patellofemoral guide. One of a total knee arthroplasty and a partial knee arthroplasty is selected intraoperatively. If total knee arthroplasty is selected, first and second covers are removed from corresponding first and second distal guiding bore. First and second distal pins through the first and second distal guiding bores are registered on the bone. If partial knee arthroplasty is selected, the anterior portion is severed and removed along a frangible groove and the distal portion is used as a patellofemoral guide.
