Background: The chondro-osseous junctional region of diarthrodial joints is peculiarly complex and may be considered to consist of the deepest layer of non-calcified cartilage, the tidemark, the layer of calcified cartilage, a thin cement line (between the calcified cartilage and the subchondral bone) and the subchondral bone. A detailed knowledge of the structure, function and pathophysiology of the normal chondroosseous junction is essential for an understanding of the pathogenesis of osteoarthrosis.

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A series of 78 patients with metastatic bone disease from prostate cancer underwent iliac crest biopsy, enabling histomorphometric quantification of eroded bone surface and bone volume in both tumour-free and metastatic bone tissue. Eroded surfaces in tumour-free specimens were high in patients with active compared to stable disease but bone volume was maintained in both groups, whilst in bone surrounding micrometastases (n = 8) eroded surfaces were further increased and bone volume reduced. Eroded surfaces within metastases were greater still but were associated with increased bone volume due to replacement of the existing trabecular tissue with abnormal woven bone, giving an overall appearance of sclerosis. These results show that the effect of prostate cancer on bone tissue is complex, involving differential disturbance of bone formation and resorption within metastases, in bone surrounding tumour invasion and in the tumour-free skeleton.

The chondro-osseous junction includes the junction between calcified and non-calcified cartilage matrices often referred to as the tidemark. A detailed knowledge of the structure, function and pathophysiology of the chondro-osseous junction is essential for an understanding both of the normal elongation of bones and of the pathogenesis of osteoarthrosis. In this study the molecular anatomy of the tidemark was studied using histochemical techniques, including lectin histochemistry, on blocks of normal cartilage from human knee joints. The tidemark stained with H and E, picro-sirius red, toluidine blue, safranin O and methyl green, but not with alcian blue in the presence of magnesium chloride at 0.05 M or above. It stained with only four lectins, those from Datura stramonium, Maclura pomifera, Erythrina crystagalli and Helix pomatia, out of the 19 used. Therefore, it is rich in collagen and contains hyaluronan, but appears to lack the glycosaminoglycans of 'conventional' proteoglycans and it expresses a very limited and distinctive lectin staining glycoprofile, which is probably attributable to specific glycoproteins. In addition, the tidemark had a distinct microanatomical trilaminate appearance. From all of these results it is clear that this part of the chondro-osseous junctional region is chemically more complex and distinctive than has previously been described.