Cartilage-bone interface

Although cartilage and bone are considered to be rigid tissues they are nevertheless living and changing throughout life. One of the retrogressive processes in cartilage is calcification, but calcification also occurs as a temporary strengthening during the replacement of cartilage by bone. Studies of the zone of calcification have shown that crystalline calcium phosphate is deposited alongside the collagen fibres. A morphometric study of the zone has now been made using novel techniques in which the surface of an epoxy-embedded thick section of undecalicified tissue is polished, stained with toluidine blue, and inspected by reflection light microscopy. Measurement of the area of stain deposition in normal tissue has led to an estimate of the area ratio for the section and, hence, the volume of calcified cartilage in the femoral head. Studies on osteoarthritic heads have revealed smaller area ratios as well as differences in distribution in the boundary layer. The significance of the data is discussed in relation to physical properties and possible remedial treatments in severe arthritis. Successful and continued functioning of articular joints is essential to normal life, but in many instances joint pain gives rise to considerable discomfort if not complete incapacity. A common cause is the breakdown of cartil