We used the information on in situ forces provided by robotics to compare two methods of posterior cruciate ligament graft fixation. Twenty porcine knees were studied using robotic technology to determine and repeat intact, deficient, and reconstructed knee motion under 110 N of posterior tibial loading at 30 degrees, 60 degrees, and 90 degrees of knee flexion. Reconstruction was performed using a bone-patellar tendon-bone graft with the distal end of the graft placed in the posterolateral aspect of the posterior cruciate ligament tibial insertion. Specimens were separated into two groups based on the femoral fixation site: the proximal or anterior aspect of the femoral insertion. Repetition of knee motion allowed measurement of the force in the intact posterior cruciate ligament and graft using the principle of superposition. The forces in the graft and the intact ligament provided additional information to evaluate graft performance. Force in the intact posterior cruciate ligament was significantly greater at 90 degrees than at 30 degrees and 60 degrees of knee flexion. The forces in both graft types were significantly lower than those of the posterior cruciate ligament, but the force in the anteriorly placed graft was significantly greater at 90 degrees than at 30 degrees and 60 degrees of knee flexion, similar to the intact posterior cruciate ligament. Thus, the anteriorly placed graft had a more physiologic increase in tension with knee flexion, when the joint provided less restraint.