CT based surgical navigation system is used to demonstrate two fundamental requirements for a practical computer-assisted surgical device. It can guide the surgeon with the accuracy required for successful graft placement, and this guidance can be achieved through a simple and intuitive interface. It utilizes a hand held tracker in the usual saw slot of total knee replacement (TKR) mechanical guides in order to get intra-operative measurements of alignment and guidance information. Once the guides are properly aligned, bone cuts are made using a traditional oscillating saw.