Improved orthopaedic bone cement formulations based on rubber toughening

Poly(methylmethacrylate) (PMMA) bone cements have been used for the fixatio n of hip and knee implants since the early 1960s.(1) Aseptic loosening, rel ated to fracture of the PMMA, continues to be the primary mode of failure f or these prostheses.(2,3) Failed prostheses must be replaced causing additi onal expense and patient trauma. Furthermore, the average lifetime of the r evised prosthesis is significantly lower than that of a primary prosthesis. (4) Recent work by Moseley and co-workers(5,6) led to the development of a prom ising new rubber toughened cement. It is comprised of a matrix of the tradi tional PMMA with dispersed rubber particles to modify mechanical properties and, in particular, improve fracture toughness. The fracture toughness of the experimental material was 167% greater than the toughness of a nontough ened control; however, the elastic modulus and compressive strength were re duced. The reductions in properties should not pose a clinical. problem bas ed on results of the implant model reported by Moseley.(5) More serious con cerns were mixing and delivery problems and high residual monomer concentra tions. The formulation and chemical/mechanical characterization of new toughened a crylic formulations that have residual monomer levels equivalent to Simplex and better mixing properties are reported.