The hypothesis that bioactive glass particulate increases the rate of bone proliferation over that of synthetic hydroxyapatite and bioactive glass-ceramic was tested in these experiments. Three types of bioactive particles-45S5 Bioglass(R), synthetic hydroxyapatite, and A-W glass-ceramic-were implanted in 6-mm-diameter holes drilled in the femoral condyles of mature rabbits. Bone growth rate was measured using an image processor. 45S5 Bioglass(R) produced bone more rapidly than either A-W glass-ceramic or hydroxyapatite. At the later time periods, 45S5 Bioglass(R) was resorbed more quickly than A-W glass-ceramic. Synthetic hydroxyapatite was not resorbed at all. Backscattered electron imaging suggested that the resorption process occurred by solution-mediated dissolution, which produced chemical changes in the enclosed particulate. It was concluded that the rate of bone growth correlates with the rate of dissolution of silica as the particles resorb.

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Various bioceramic materials were implanted into 6-mm-diameter holes made in the femoral condyles of mature Japanese white rabbits using different-sized granules to find an optimal material and granule diameter for use as a bone graft. Bioceramics include a bioinert ceramic (Alumina), surface-bioactive ceramics [hydroxyapatite (HAp) and Bioglass(R)], and resorbable bioactive ceramics [alphatricalcium phosphate (alpha-TCP), beta-TCP, tetracalcium phosphate (TeCP), Te. DCPD, Te. DCPA, and low-crystalline HAp]. Granule sizes were 100-300, 10, and 1-3 microm. Bone growth behavior varied with the kind of bioceramic and the size used. For surface-bioactive ceramics, 45S5 Bioglass(R) led to more rapid bone proliferation than synthetic HAp. In resorbable bioactive ceramics, the order of resorption was: low-crystalline HAp and OCP > TeCP, Te DCPD, Te DCPA > alpha-TCP, beta-TCP. In terms of biocompatibility, alpha-TCP was better than beta-TCP.

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With the increased clinical interest in metal-on-metal and ceramic-on-ceramic total-hip replacements (THRs), the objective of this hip simulator study was to identify the relative wear ranking of three bearing systems, namely CoCr-polyethylene (M-PE), CoCr-CoCr (M-M) and ceramic-on-ceramic (C-C). Volumetric wear rates were used as the method of comparison. The seven THR groupings included one M-PE study, two M-M studies and four C-C studies. Special emphasis was given to defining the 'run-in' phase of accelerated wear that rigid-on-rigid bearings generally exhibit. The hypothesis was that characterization of the run-in and steady state wear phases would clarify not only the tribological performance in vitro but also help correlate these in vitro wear rates with the 'average' wear rates measured on retrieved implants. The implant systems were studied on multichannel hip simulators using the Paul gait cycle and bovine serum as the lubricant. With 28 mm CoCr heads, the PE (2.5 Mrad/N2) wear rates averaged 13 mm3/10(6) cycles duration. This was considered a low value compared with the clinical model of 74 mm3/year (for 28 mm heads). Our later studies established that this low laboratory value was a consequence of the serum parameters then in use. The mating CoCr heads (with PE cups) wore at the steady state rate of 0.028 mm3/10(6) cycles. The concurrently run Metasul M-M THRs wore at the steady state rate of 0.119 mm3/10(6) cycles with high-protein serum. In the second Metasul M-M study with low-protein serum, the THR run-in rate was 2.681 mm3/10(6) cycles and steady state was 0.977 mm3/10(6) cycles. At 10 years, these data would predict a 70-fold reduction in M-M wear debris compared with the clinical PE wear model. All M-M implants exhibited biphasic wear trends, with the transition point at 0.5 x 10(6) cycles between run-in and steady state phases, the latter averaging a 3-fold decrease in wear rate. White surface coatings on implants (coming from the serum solution) were a confounding factor but did not obscure the two orders of magnitude wear performance improvement for CoCr over PE cups. The liners in the alumina head-alumina cup combination wore at the steady state rate of 0.004 mm3/10(6) cycles over 14 x 10(6) cycles duration (high-protein serum). The zirconia head-alumina cup THR combination wore at 0.174 and 0.014 mm3/10(6) cycles for run-in and steady state rates respectively (low-protein serum). The zirconia head and cup THR combination wore slightly higher initially with 0.342 and 0.013 mm3/10(6) cycles for run-in and steady state rates respectively. Other wear studies have generally predicted catastrophic wear for such zirconia-ceramic combinations. It was noted that the zirconia wear trends were frequently masked by the effects of tenacious white surface coatings. It was possible that these coatings protected the zirconia surfaces somewhat in this simulator study. The experimental ceramic Crystaloy THR had the highest ceramic run-in wear at 0.681 mm3/10(6) cycles and typical 0.016 mm3/10(6) cycles for ...