Study of Factors Affecting Taper Joint Failures in Modular Hip Implant Using Finite Element Modelling
The replacement of the natural hip with artificial components is a well established procedure in orthopaedic medicine to alleviate pain from the diseased joint. The total hip replacement (THR) consists of a femoral component or stem and an acetabular cup. These are made as either one piece or modular designs. Modular femoral components have become popular among surgeons because neck length and offset can be adjusted intraoperatively, providing increased versatility without any need for a large inventory. In addition, modular heads allow for mixed alloy systems such as the combination of a titanium alloy stem with a cobalt-chromium or ceramic head. Apart from the neck/head connection, there are femoral stem designs with extra areas of modularity. Examples of these prostheses are the S-ROM (Joint Medical Products, Stanford, Connecticut), the Infinity (Dow Corning Wright, Memphis, Tennessee), the RHMS (SmithNephew Richards, Memphis, Tennessee), and PROFEMUR Hip System (Wright Cremascoli Ortho SA, France). A major drawback for all modular orthopaedic devices is that each modular component interface becomes a potential site for corrosion, wear, fretting and fatigue of mating surfaces (Collier et al., 1992; Manley & Serekian 1994; Hallab & Jacobs, 2003; Goldberg & Gilbert, 2003; Hallab et al., 2004; Gilbert et al., 2009; Rodrigues et al., 2009). The products of these interface processes are believed to cause tissue reactions that lead to implant loosening and subsequent failure of the arthroplasty (Amstutz et al., 1992; Harris, 1994; Kraft et al., 2001; Goldberg et al., 2002). Thus, to make implant designs successful in clinical applications, these concerns need to be adequately addressed during the design stage of the prosthesis in conjunction with the implant strength and integrity of the implant-host bone system. Types of failures often encountered in modular hip implants are dissociation, corrosion, wear; fretting and fatigue of mating metal surfaces (Goldberg et al., 2002, Sporer et al., 2006; Rodrigues et al., 2009). There are varieties of design and material factors that may influence the failure of specific components. The most significant of these is fretting because is almost impossible to prevent and in many cases may lead to other form of failures. 8