Metals for joint replacement

In this chapter the properties and surgical use of steel, titanium and cobalt-based alloys and tantalum are overviewed. The design of total hip replacements (THRs) is described briefly followed by a detailed description of failure modes of THRs, including material and nonmaterial-related modes. Of special interest are several serious failure modes, including the roles of impingement/contrecoup edge loading and wear in the trunnion leading to the widely publicised failures of the metal-on-metal hip resurfacing and large-diameter head arthroplasties. These deleterious features went unnoticed in cyclic loading simulations but led to serious failures in clinical practice. Nanoparticles and metal ions released cause adverse reactions to metal debris: pain, fluid collection, pseudotumours, tissue necrosis, ‘particle disease’ and hypersensitivity reactions. The latest clinical results are presented separately for cemented and cementless THRs and materials of the femoral stems. The study outcomes and statistical methods used for the evaluation of different designs are discussed, along with the importance of cohort studies and national joint arthroplasty registries. These are collecting limited datasets on almost all implanted and explanted prostheses in a defined country or region and can identify long-term differences in implant survival and compare the influence of patient factors. Among features that are important as future trends, we selected patient-specific implants, resurfacing implants, bone saving mini-implants (short stems), isoelastic implants and implant coatings aimed to improve osteointegration, antibacterial activity, better adherence to bone cement and tribological properties of the bearing couple. The future prosthesis design should provide a portfolio of implants with a wide range of dimensions and implant shapes for optimal fit to the patient’s geometry and different functionalities.