Tham khảo tài liệu 'modern tribology handbook 2010 part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | FIGURE Schematic diagram of the artificial hip joint. Schmalzried et al. 1992 . Although joints do not wear out they produce many millions of wear particles and it is the adverse biological reaction to these particles that leads to bone resorption and to loosening and failure Shanbharg et al. 1994 Howie et al. 1993 . Currently there is considerable attention focused on the wear wear debris and adverse biological reactions in artificial joints Fisher 1994 and this is discussed in Section . Over the last 40 years several different bearing couples have been used in joint replacements metal on metal ceramic on ceramic polytetrafluoroethylene PTFE on metal and polyethylene on metal. By far the most frequently used bearing couple has been ultrahigh-molecular-weight polyethylene UHMWPE articulating on ceramic or metal femoral heads in the hip Figure and metal femoral condyles in the knee. There has been good agreement between the clinical measurement of wear and in in vitro simulators in UHMWPE cups in the hip. For smooth polished metal femoral heads wear rates of about 40 mm3 year have been recorded both in vivo and in vitro and this corresponds to a linear penetration of mm year. Hence with this wear rate it would take an 8-mm-thick cup 80 years to wear out. Wear is however accelerated by damage to the femoral head oxidative degradation of the UHMWPE and also by the use of larger-diameter heads and cups. Clinical and laboratory studies have shown that damage to the femoral head and aging of the polyethylene can independently accelerate the wear by a factor of 2 and hence with these combined effects it is possible to obtain wear rates of between 100 and 200 mm3 year clinically Livermore et al. 1990 . Explant studies have shown osteolysis associated with cumulative wear volumes of 500 to 1000 mm3 and therefore it is not surprising that the incidence of wear debris-induced osteolysis increases markedly after 10 years. Clinical evidence indicates that .
