The twofold purpose of this study was to develop an intraoperative technique to assess isometric positioning of posterior cruciate ligament grafts and to demonstrate the rationale for postoperative immobilization of the knee in full extension after a posterior cruciate ligament reconstruction. Multiple femoral fixation sites were selected on the medial intercondylar notch and the posterior cruciate ligament substitute was assessed for changes in length and tension at each of these sites during knee flexion from 0 degree to 120 degrees. The most isometric and isotonic femoral fixation site was localized over a small area slightly distal to the center of the medial intercondylar notch surface. This isometric point can be identified intraoperatively using recognizable surface markers within the knee. When a posterior stress was applied to the proximal tibia, the posterior cruciate ligament substitute showed the least increase in tension and length when the knee was locked in full extension for all of the potential femoral attachment sites assessed. This suggests that postoperative immobilization should be maintained in full extension to limit the stress placed on the posterior cruciate ligament reconstruction.