Tetracycline labelling methods of measuring the growth of bones in the rat.

The observation of Milch and his associates in 1957 that tetracycline becomes localised in areas of new bone formation has been confirmed on many occasions (Milch, Rail and Tobie 1958: Frost, Villanueva and Roth 1960; Harris 1960; Muzii 1961), and in 1960 Harris suggested that tetracycline might be suitable for use as a marker whereby the rate of bone formation could be measured. Since then a number of workers have studied the growth of compact lamellar bone by tetracycline labelling methods (Frost 1961, 1963; Harris, Jackson and Jowsey 1962; Urist, Zaccalini, MacDonald and Skoog 1962). Difficulties, however, arise in the interpretation of any measurements made on compact lamellar bone. Osteoblastic activity is irregular in such bones and varies from one part ofthe bone to another, so that a large number of serial sections have to be examined to obtain a true picture of the amount of osteoblastic activity in the bone. This report is concerned with the use of tetracycline labelling in bones which grow in a relatively simple way such as the tibia ofthe rat. With tetracycline labelling, the normal growth pattern of this bone both in length and in width has been determined and compared with radiological methods.