Investigation of the growth and structure of the tibia of the rabbit by microradiographic and autoradiographic techniques.

Previous investigations on the structure and growth of long bones have been made by many and varied techniques. As early as 1727 Hales first demonstrated experimentally by drilling holes to act as markers that in the growing bone the markers always remained at the same distance apart and that there was therefore no interstitial growth. This has been subsequently confirmed by many workers using the technique of markers of madder feeding (Duhamel 1742, Hunter in about 1772, Payton 1931-32, Brash 1934, Bisgard and Bisgard 1935) and of the radiographic study of the lines of arrested growth (Harris 1933). It was also noted that growth in width was different along the length of the bone (Duhamel 1743). Lacroix (1951) studied transverse growth in detail by routine histological techniques. It is now accepted that, in general, transverse growth depends on the formation of new bone on the endosteal surface of the metaphysial funnel and on the periosteal surface of the cylindrical shaft, together with simultaneous removal of bone from the periosteal and endosteal surfaces respectively at the same sites. Studies with radioactive isotopes have confirmed these findings and added many new details. Radioactive phosphorus has been used as a tracer to demonstrate the growth of the tibia-fibula in rats (Leblond et al. 1950). A single intravenous injection of the radioactive isotope was given and the animals sacrificed at various times after injection. In confirmation of previous ideas these authors have shown how endosteal deposition on the metaphysis associated with periosteal resorption as part of the remodelling process of the funnel accounts for increase in length of the cylindrical shaft of the bone as the animal grows older without “ interstitial growth of bone.” 45Ca has also been used in rats (Tomlin, Henry and Kon 1953). In these experiments rats thirty days old received a daily diet containing radioactive calcium. The growth of the femur and humerus was then studied by observing the position of the nonradioactive bone with respect to the radioactive bone at various time intervals after starting the diet. The results show how differences in deposition of new bone on the anterior and posterior walls are related to the curvatures of the bone cortex. Observations on the uptake of radioactive strontium in rabbits (Kidman et al. 1952, Jowsey et al. 1953a, Jowsey, Owen and Vaughan 1953b) and in pigs (Comar, Lotz and Boyd 1952) have shown that the sites of deposition of this isotope in the bones correspond with those of the formation of new bone tissue, and many new facts concerning its rate of uptake and position in animals of different ages have been recorded. Previous work with the autoradiographic technique has been done using longitudinal sections of bone. There are, however, inherent limitations to the information which can be obtained in this way. In the present investigation, which is a study of the growth of the proximal half of the tibia of the rabbit, it was therefore decided to use transverse sections, making use of both microradiographic and microautoradiographic techniques. Microradiographs of transverse sections reveal structural features not evident under the ordinary microscope-in particular, variation in degrees of calcification in different areas of bone. For the preparation of the autoradiographs, 90Sr, which emits p particles of maximum energy 0’53 mev and has a half-life of twenty-five years, was used as a tracer. The animals were injected with a single dose of carrier-free 9#{176}SrC12 solution and killed at various times after injection. A study of the position of the isotope incorporated at the time of injection was then made.