Composite Implant for Bone Replacement

Abstract

A procedure is described for designing prosthetic implants made of composite materials used in central bone and combined joint and bone replacements. The primary objective was to arrive at an implant made of fiber reinforced composites which has a higher bone growth stimulus and a lower micromotion level than titanium alloy (Ti6Al4V) implants currently in use. A secondary objective was to provide a means by which the physician can select, rapidly and with ease, the proper implant for a specific patient. To achieve these objectives, a procedure was developed consisting of three major elements. The first is a performance parameter which indicates the relative merits of different implant designs and takes into account that bone growth and micromotion have different importance from a clinical point of view. This relative importance is taken into account with weighting factors, the values of which were estimated from a survey of orthopedic surgeons. The second element of the procedure is a finite element code for calculating the strains in the bone, which are the parameters of importance in evaluating the implant's performance. The third element is a strain library which stores strains precalculated for a large number of different patient characteristics and different implant types. The strains for the specific patient under treatment are obtained by interpolation of the data in this strain library. The performance of an implant is then evaluated based on these patient specific strains. An example is presented for implants made of graphite AS4/PEEK composite. The results indicate that, in most applications, composite implants have better performances than titanium alloy implants both from the point of the overall implant performance and from the points of view of bone growth and micromotion.