In-vitro experimental determination of knee stiffness

The quantification of knee stiffness, i.e. the relation between applied loads and bone displacements, is fun-damental both for the clinical discrimination between healthy and pathological states and for the definition and validation of numerical models of the joint. Considering the knee as a 1 unresisted degree-of-freedom (dof) system, its stiffness analysis requires the application of constant loads for each value of the flexion an-gle, taken as free parameter of the unresisted motion, while recording the variation of the remaining 5 dofs describing the relative position and orientation of the femur with respect to the tibia. In spite of the relevance of these data, no many studies are available in the liter-ature on this topic [1-4]. In particular, the displacements/rotations not corresponding to the loading direc-tion were not deeply investigated. In this study, knee stiffness was characterized by a loading rig [5]. The results for the drawer test are shown as representative.