In vivo contact pressure in the knee during a flexion–extension movement

All the geometrical acquisitions of the inner structures of the knee were obtained from MRI images in order to get in vivo models non-invasively. First the kinematics of one subject’s knee was acquired, thanks to a dedicated MRI protocol (Sangeux et al. 2006). A non magnetic flexion guide was used for reproducibility purpose and the continuous movement of the knee was assessed from a finite set of 4 knee positions in the range of 0–638 of flexion. The kinematics of the knee was described with helical axes. The finite element model was composed of the bones, the cartilage and the menisci. The geometrical modelling was performed in a pre–post finite element software. The bones were considered as rigid so a simple surface mesh was employed. For the cartilage and the menisci a dedicated sub-routine was designed in order to build a volumic mesh based on each structure thickness map. The material properties of the soft tissues were derived from the literature (Donahue et al. 2003), the cartilage was considered as isotropic and elastic and the menisci as a transverse isotropic elastic tissue. The model integrate cartilage/cartilage and meniscus/ cartilage contact. The model was validated in pure compression by the comparison of the contact pressure area determined by the model and the nodal distance from the MRI images.