Decreased Bone Mineral Content = Rickets: A Misleading Equation

Sir .—Rickets is a disease characterized by decreased mineralization of bone, a relative paucity of calcium and phosphate (apatite) in a matrix of cartilage. 1 Therefore, one would anticipate a decrease not only in the total amount of minerals (ash) but also in the concentration or density of these minerals. If the volume of the matrix is constant (ie, no bone growth), then the estimates of total bone mineral and bone mineral content (BMC) per cubic centimeter are linearly correlated. If, however, bone size increases, as can happen in both normal and rachitic bone, 1 then BMC could increase or remain constant, while bone density might remain constant or fall. Therefore, a distinction must be made between delayed bone growth (slowed matrix formation) and decreased bone density. Delayed bone growth may be one manifestation of widespread nutritional deficiencies, whereas rickets results from deficiencies of or failure to utilize calcium, phosphate,