Analyzing the patellar tendon force during quadriceps muscle exercise

The mechanics of the knee was analyzed in the sagittal plane to study the role of patellar tendon as influenced by the placement of external flexing loads on the tibia and by translation of the tibial bone 7mm anterior to the femoral bone during the flexion range 0-120°. Anatomical parameters and measurements for orientations and moment arms of the patellar tendon during the flexion range were taken from experiments on cadaver knees available in the literature. The analysis suggests that the force in the patellar tendon varies directly with the distance of the external flexing load placed distal to the tibial surface. This effect is uniform throughout the joint flexion range. Further, 7mm anterior translation of the tibia relative to the femur resulted in significantly reduced anterior component of the net shear force for all flexion positions and all placements of loads distal to the joint line. This has relevance to ACL-deficient knees where large tibial translations may be necessary to compensate for the deficiency. Two critical factors that may require special attention to protect the ACL during rehabilitation exercises are the flexion angle and the position of the flexing load below the tibial surface.