In vivo contact pressure in the knee during a flexion – extension movement M. SANGEUX†, F. MARIN†, F. CHARLEUX‡ and M.-C. HO BATHO†* †Laboratoire de Biome ´canique et Ge ´nie Biome ´dical, UTC, France ‡Centre d’Imagerie Me ´dicale Avance ´ de Compie `gne, France 1. Introduction The knee is a complex joint with various pathologies or injuries subjected to high mechanical conditions. As these pathologies highly depend on each patient the objective of the present study was to develop a procedure to build in vivo personalized knee finite element models that can deduce in vivo contact pressure in the cartilage of the knee during a flexion–extension movement. 2. Materials and methods 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. 3. Results One first result was a cartilage thickness map from the dedicated meshing sub-routine. This map is presented on the femur cartilage (figure 1). The second result is the cartilage/cartilage contact pressure pattern during a knee flexion–extension movement presented on figure 2. Figure 3 presents the comparison between model outputs and nodal distance from MRI images outlines. Computer Methods in Biomechanics and Biomedical Engineering ISSN 1025-5842 print/ISSN 1476-8259 online q 2007 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/10255840701478877 *Corresponding author. Email: marie-christine.hobatho@utc.fr Figure 1. Cartilage thikness map for the femur (scale in mm). Available in colour online. Computer Methods in Biomechanics and Biomedical Engineering, Supplement 1, 2007, 97–98