The influence of joints and soft tissue on the natural frequency of the human tibia using the impulse response method

The influences of the joints adjacent to the human tibia, the surrounding soft tissue and the fibula on the vibrational parameters of the tibia (that is natural frequency, mode shape and damping ratio) are in need of clarification. Using five cadaveric human legs, the resonant frequency and damping ratio were measured with an accelerometer placed on the medial tibial condyle while the medial malleolus was impacted by an impulse hammer. The legs were subsequently dissected and the measurements were made in six conditions. The mode shape was obtained by use of modal analysis. Hammer impacts were given at 15 points along the three surfaces of the tibia, while an accelerometer was attached to the surface of the medial malleolus. Resonant frequencies ranged from 275 to 405 Hz in the intact specimens and successively increased with removal of the skin, muscles and foot, and then decreased with the removal of the femur and the fibula. Damping ratios successively decreased. The transitional pattern of natural frequencies was similar to that of the resonant frequencies. The mode shape represented the first bending mode and it corresponded to the condition of the tibia in which the proximal and distal ends of the bone were free.