Calcium (Ca) is an essential element of all cells and organisms. It is involved in many cellular functions, e.g. in cell signalling, enzyme secretion, cell aggregation, cell division and muscular contraction . Late in phylogeny, Ca became a major element of the skeleton only in higher vertebrates. Functionally replacing cartilage, bone has a higher compression and tensile strength . To carry the same weight, the cross-sectional area of cartilage must be 5 times greater than that of bone; therefore, the cross-sectional articular cartilage area is much larger than the adjacent cortical bone area.