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Analyses of the tidemark on human femoral heads. I. Histochemical, ultrastructural and microanalytic characterization of the normal structure of the intercartilaginous junction.

The tidemark as a boundary between non-calcified and calcified articular cartilage has a complicated structure and fulfils various physiological functions. 25 human femoral heads from healthy joints were examined. In non-decalcified preparations three structural components of the tidemark were demarcated: (1) the PAS-positive, proteoglycan-containing tidemark line adjacent to the basal cartilage, (2) the sublinear light-coloured zone and (3) the demarcation line to the calcified cartilage. Using scanning electron microscopy, the tidemark was characterized as an electron-dense impression between hyaline and calcified cartilage. The presence of specific architecture and orientation of collagenous fibres could not be shown. Concentrations of calcium, phosphorus and sulphur could not be detected in the tidemark by means of an X-ray microanalyzer. A morphological model of the tidemark region was established, which represents the intercartilaginous junction as a double layer of substantially and functionally different surfaces.