MICRORADIOGRAPHY OF BONE RESORPTION 



461 



Fig. 6. Microradiograph of a cross section through the mid-shaft of the 

 femur of a 67-year-old female with osteoporosis. There are a large number of 

 resorption cavities and a high proportion of incompletely closed osteons. 

 (Xll.) 



of bone resorption are very much higher in this group than in the 

 normal series ( Fig. 6 ) . In older individuals there appears to be some 

 equilibrium, and the amount of resorption decreases toward normal 

 values while the levels of bone formation remain the same. The 

 porosity figures are significantlv higher in the osteoporotic group 

 than in the normal series, which is to be expected since the porosity 

 represents the cumulative effect of the difference between the levels 

 of resorption and of formation. The values for cortical thickness are 

 generally lower than normal. It would seem, therefore, that osteo- 

 porosis is the result of increased resorption of bone, which in the 

 mid-shaft of the femur appears to be a factor of 2 or 3 times above 

 normal values. These differences are exaggerated in the iliac crest, 

 both in the osteoporotics and in the normal series, and for this rea- 

 son the iliac crest is probably a better biopsy site. 



