462 J. JOWSEY 



Paget' s Disease 



Grossly this a])normality varies in its appearance from one of de- 

 creased density to one of sclerosis, and the microradiographic ap- 

 pearance of three stages — porosis, sclerosis, and presarcomatous — 

 has been described bv Kelly et ah ( 1961 ) . Figure 7A demonstrates 

 the porotic stage, where bone resorption is going on most actively 

 at levels 15 times above the normal level. A higher magnification 

 (Fig. 7B) shows the characteristic mosaic appearance and great 

 variation in degree of mineralization and also the very irregular 

 surfaces of the bizarre resorption cavities associated with rapid 

 disappearance of tissue. At short intervals after injection of tetra- 

 cvcline such irregular surfaces are strongly labeled, indicating par- 

 ticularly high metabolic activity. Quantitative values for formation 

 and resorption are in the order of 20 times the normal levels. 



Hi/perparathijwidism 



Earlv stages of hyperparathyroidism appear microradiographically 

 like osteoporosis. However, advanced hyperparathyroidism accom- 

 panied bv a much elevated blood calcium level results in calcification 

 of the fibrous connective tissue in the haversian canals and resorp- 

 tion cavities (Fig. 8). Both bone resorption, which is a factor of 10 

 or more times above the normal level, and bone formation, which 

 is also increased, appear to be going on rapidly. 



In both Paget's disease and hyperparathyroidism the increased 

 resorption levels may result in generalized or local porosis and even- 

 tually fracture of the bone. 



Osteogenesis Imperfecta 



Measurements of bone formation and resorption show that in 

 osteogenesis imperfecta there is both a reduction in formation to 

 less than a third of its normal value and a threefold increase in the 

 amount of resorption. It would seem that this situation has existed 

 for some time, since there is a considerable amount of unremodeled 

 primary periosteal and endochondral bone with large resorption 

 cavities, and the cortex is very thin (Fig. 9). The bone itself appears 



