Analyzing the role of patellar tendon force during flexion of the knee

The mechanics of the knee was analyzed in the sagittal plane to study the role of patellar tendon in resisting a flexing load and in translating the tibia anterior or posterior to the femur. The effect of load placement at different positions distal to the tibial surface was analyzed during the flexion range 0-120o. Data for orientation and moment arm of the patellar tendon during the flexion range was taken from experiments on cadaver knees available in the literature. The results and analysis suggest that during quadriceps strengthening exercises distal placement of flexing loads on the tibia, in comparison to more proximal placements, results in larger muscle forces. However, such loads are also associated with larger translations of the tibia relative to the femur, thus, loading the cruciate ligaments. Particularly, the anterior cruciate ligament is predisposed to loading due to load placements far distal on the tibia in the low-to-mid flexion range. Therefore, rehabilitation exercises requiring protection of the ligament need attention for the position of external flexing load on the tibia as well as the flexion angle at which the exercise is performed.