An investigation into the mechanical and biological properties of acrylic bone cement containing triphenyl bismuth (TPB) as an alternative radiopacifier

Abstract

Total joint replacement is the most successful method of treating end-stage arthritis. It significantly improves the quality of life and the functional capability of patients suffering from arthritis. Currently an estimated 40,000 total joint arthroplasties are performed each year in the United Kingdom, and over 42% of these are performed in patients younger than 65 years. Poly(methylmethacrylate) bone cement is used to fill the space between the bone and the prosthesis in joint replacements and thus forms a mechanical bond between the two surfaces. The cement layer transfers the load from the prosthesis to the bone and increases the load bearing capacity of the implant-cement-bone system. Surgeons require bone cement to be radiopaque on radiographs in order to monitor the position of the implant after a joint replacement surgery. Therefore heavy metal salts such as barium sulphate and zirconium dioxide are added to bone cement to impart such radiopacity. The addition of these radiopacifiers, however, degrades the mechanical properties of the bone cement due to the lack of chemical bonding between the radiopacifier and the polymer matrix. Barium sulphate is known to adversely affect the mechanical strength and fracture toughness of bone cement. Various studies have also shown that barium sulphate and zirconium dioxide may contribute to the pathological bone resorption of aseptic loosening by enhancing macrophage-osteoclast differentiation. In this study an organo-bismuth compound, triphenyl bismuth (TPB) has been investigated as a potential radiopaque alternative to barium sulphate in bone cements. The inclusion of TPB has been shown to improve the mechanical properties of bone cement including fracture toughness. Furthermore, it has also been shown to cause less bone resorption, which is usually associated with aseptic loosening in joint replacement.