FORMATION OF A FIBROUS TISSUE AT THE BONE/IMPLANT INTERFACE P. Büchler 1,2 , D.P. Pioletti 1,2 and L.R. Rakotomanana 3 1. ABSTRACT A model of the tissue differentiation at the bone-implant interface is proposed. The basic hypothesis of the model is that the mechanical environment determines the tissue differentiation. The stimulus chosen is related to the bone-implant micromotions. Equations describing the evolution of the interfacial tissue are proposed and combined with a finite element code to determine the evolution of the fibrous tissue around prostheses for clinical situations. The model is applied to a simplified case of a hip prosthesis. 2. INTRODUCTION The long-term stability of implants is a major concern for joint arthroplasties. Formation of a fibrous interface between the bone and the implant is a frequent problem. The fibrous interface looses the implant, which commonly causes pain and eventually leads to a new surgical procedure. The biological factors causing growth of the fibrous interface are not completely clear. Authors point out the role of wear particles on bone osteolysis [1, 2]. Aspenberg [3] found that the mechanical environment of the bone cells is more important for the fibrous formation process than the presence of particles. Mechanical variables are assumed to be involved in the formation of the fibrous tissue like the hydrostatic compression [4, 5], the fluid pressure [6, 7] and the fluid velocity [8, 9]. We suppose that the most important parameter is the bone/implant micromotions. We know from the traditional two-stage procedure used for the endosseous dental implant that the tissue 1 Orthopedic Hospital, Av. Pierre-Decker4, 1005 Lausanne, Switzerland 2 Biomedical Engineering Lab., Swiss Federal Institute of Technology, 1015 Lausanne, Switzerland 3 Institute of Mathematics, University of Rennes 1, Campus de Beaulieu, 35042 Rennes, France Keywords: Fibrous tissue, Differentiation, Evolution, Prosthesis, Finite element