We have developed a surgical navigation system to examine surgical technique for total knee replacements and to characterize knee kinematics in the operating room. This tool allows us to characterize the in vivo properties of osteoarthritic knees and to measure knee motion following total knee replacement. We performed the first intra-operative characterizations of the three-dimensional kinematics of advanced osteoarthritic knees and the first recordings of the change in kinematics as a result of total knee arthroplasty. This work is done with the Institute for Computer-Assisted Orthopaedic Surgery in Pittsburgh, Pennsylvania.