Histological studies on bone from the human iliac crest have suggested that if the customary techniques of labeling in vivo with certain fluorochromes such as tetracycline are replaced or augmented by simple whole tissue staining in vitro using the same reagents, differences in the pattern of extracellular fluorescence between normal and pathological states are retained. In particular, the association of the fluorescence with the calcification front in stained examples is closely comparable to similar examples that have been labeled (r = 0.988, p < 0.001) and to other tinctorial methods (r = 0.891, p < 0.001). While the stain alone lacks the time lapse of multiple labels, when administered some days after a single label at the time of biopsy, it provides an effective second marker and a measure of mineralization rate that does not differ significantly from that using double labels. Moreover, since the problems of toxicity are avoided by staining, a range of contrasting fluorochromes previously restricted to animal studies may now be used in man. In particular, the enhanced color differentiation brought about by the combination of tetracycline label followed by xylenol orange stain improves image resolution and greatly aids interpretation.
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