Tetracycline bone labeling in anatomy

Tetracyclines are deposited in vivo at centers of active bone formation, and can be seen by fluorescence microscopic examination of undecalcified bone sections. With this marker, the rate of bone formation at the level of the osteon can be measured, and is taken to indicate the speed of bone formation at the level of the osteoblast. When the number of bone‐forming centers is then counted, it becomes possible to compute: ( 1 ) the number of new centers initiated per unit time, which number is taken to indicate the number of new osteoblasts created from the osteoprogenitor cell (mesenchymal cell) pool; ( 2 ) the rate of bone formation averaged over the whole sample, which is the form of protein anabolism characteristic of bone. Therefore the tetracycline‐labeling technique permits the quantitative analysis of skeletal growth, as well as the maintenance of the mature skeleton, in terms of tissue dynamics and cell population dynamics. Of major importance in the design of future studies is the frequent finding that abnormalities in the rate of bone formation over the whole tissue may be the opposite of abnormalities in the rate of bone formation at the level of the osteoblast. This situation can exist because osteoprogenitor cell behavior can – and frequently does – produce major changes in the total number of functional osteoblasts, changes which do not correlate with changes in the behavior of individual osteoblasts.