HISTOLOGICAL CHANGES AFTER IRRADIATION 



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Autoradiography indicate that deposition of most radioactive materials 

 is greatest in the areas of maximum growth in length of the bones. The 

 isotopes are also deposited along the periosteum and parts of the endos- 

 teum. Where there is intense radioactivity, osteocytes degenerate. 

 The bone of the metaphysis is devitalized to a greater extent than that 

 of the cortex. But in rats five and six months after radium dosage of 

 0.06 juc/g, even the dense cortical 

 bone contains large numbers of 

 lacunae devoid of their bone cells. 

 As after X irradiation, osteoblasts 

 disappear and interdigitation of bone 

 and cartilage at the epiphyseal line is 

 decreased, often leading to complete 

 separation of epiphyseal cartilage 

 from spongiosa and arrest of growth 

 in length. After low doses of short- 

 lived radioactive isotopes, as after X- 

 ray dosage, repair occurs and growth 

 in length is resumed. Longer-lived 

 agents and higher doses cause an 

 overgrowth of atypical metaphyseal 

 bone which later becomes devital- 

 ized. This bone varies in appearance 

 by the number of osteocytes, coarse- 

 ness of connective tissue fibers, and 

 density of the matrix ; it never shows 

 evidence of intracartilaginous ossifica- 

 tion. It may persist in the center of 

 the shaft months after injection of the 

 radioactive material. The old meta- 

 physis with its devitalized bone is 

 very weak and fractures often occur 

 here. This is also the site in which 

 osteogenic sarcomas develop. Several 

 examples of this occurred in radium 

 dial painters (Martland, 1931). In 

 rats receiving doses that permit sur- 

 vival for a long enough time, this 

 atypical overgrowth is outstripped by 



the normal growth mechanism and growth in length of the bone is 

 resumed. At still lower doses there are sometimes suggestions of partial 

 resorption of the old spongiosa and atypical bone even with the long- 

 lived a emitters. 



However, where bone growth has ceased, as in adult mice, the picture 



Fig. 17-4. Section of proximal epiphy- 

 sis of rat tibia, five months after the 

 injection of 0.125 juc/g of radium 

 showing the old metaphysis at (a), 

 new bone at (6), and the new meta- 

 physis at (c). (After Heller, 1948.) 

 9X. 



