ANALYSIS OF SECTIONS OF IMPLANTED MACROPOROUS CALCIUM-PHOSPHATE BONE SUBSTITUTES BY PROTON-INDUCED X-EMISSION METHOD AND ENERGY-DISPERSIVE SPECTROMETRY

The osseointegration of porous calcium phosphate ceramics once implant ed evolves in several stages. The mechanism of integration of such mat erial usually is evaluated by histologic analysis. The trace elements present in bone can be detected in the ceramic and help to provide a s emiquantitative evaluation of osseointegration. Two different methods of microanalysis, energy-dispersive spectrometry (EDS) and proton indu ced x-emission (PIXE) were used in this study to determine the appeara nce of trace elements (Zn, Sr, and Fe) present in bone at the implanta tion site containing the ceramic. Porous HA-ceramic cylinders were imp lanted in the cortical bone of sheep femurs for periods ranging from 2 to 36 weeks. Thick sections of the implant-containing bone were made at the end of the implantation period. A scanning line with proton or electron impacts 0.5 mm apart was plotted from the edges of the cortic al bone across the implanted ceramic and the resulting x-ray spectra w ere determined. Following EDS analysis, the sections were surface-stai ned, observed under a light microscope, and the pore volume occupied b y bone tissue was measured. The spectra obtained by PIXE method showed two regions for each element characterising either the bone tissue or the ceramic. Zinc and strontium present in the bone tissue, but absen t from the ceramic, appeared 8 and 12 weeks after implantation, respec tively. The concentration of iron present in the implant decreased wit h time. EDS showed no significant level of either element in the bone or the ceramic. Histologic observation revealed that immature bone inv aded the pores of the outer layer of the ceramic as early as 2 weeks a fter implantation. The ceramics were totally osseointegrated 20 weeks after implantation, although ceramic degradation continued for longer. In this experiment, the PIXE method was apparently sufficiently sensi tive for monitoring the amount of trace element appearing in bone-impl anted material.