Use of the principle of virtual work reciprocity to explain the human joint motion: application to the knee

The study of natural motion of human joints, i.e. the unresisted motion that the articulations exhibits in the absence of external loads, provides insights into their physiology. The natural motion represents the baseline condition upon which deformations of passive structures (i.e., ligaments and cartilage) take place when loads are applied. During natural motion, the strain energy density stored within ligaments and cartilage is minimized, reducing the chance of microdamage occurrences and the corresponding metabolic cost for tissue repairing. The study of the natural motion is thus fundamental to understand the joint physiology. In this work, the geometrical arrangement of the constraints necessary for the joint natural motion is theoretically derived from the application of the principle of virtual work. The implication of this general approach will be derived and experimentally verified for the knee.