MICRORADIOGRAPHY OF BONE RESORPTION 455 



of a section, as a percentage of the inactive surface in that same 

 area. A standard sample area in each site is analyzed. In the mid- 

 shaft of the femur one-third of an entire cross section constitutes 

 the sample area, one-quarter of the area being taken from each of 

 four quadrants. Analysis of smaller samples produces data with 

 considerably less significance. 



Measurements of the porosity of the bone are also made. In cor- 

 tical bone from the femur this porosity measurement consists of the 

 percentage of osteons which are less than two-thirds closed; that 

 is, the diameter of the central canal is more than one-third the 

 diameter of the whole osteon up to its cement line. The thickness 

 of the cortex in the specimens is also measured. 



Summary 



Undecalcified bone sections are cut from normal and pathological 

 material and microradiographs made. Bone formation and resorption 

 are identified and quantitative measurements made on photographic 

 enlargements. Bone porosity is also measured. 



Discussion of Results 



Resorption 



Resorbing surfaces are obviously places of great metabolic and 

 chemical activity and are in intimate contact with the body fluids as 

 indicated by electron microscope work (Scott and Pease, 1956; 

 Cameron and Robinson, 1958) and the uptake of the rare earths 

 (Jowsey et al., 1958). Calcium^"' and tetracycline are also deposited 

 on these surfaces for a short time ( Fig. 2 ) , possibly by an exchange 

 mechanism, and may account to some extent for some of the skeletal 

 retention found at short intervals after an injection of radioisotopes 

 such as Ca^^ in areas of fracture or in osteoporotic bone, where a 

 great deal of resorption is known to be occurring. Areas of par- 

 ticularly active resorption appear microradiographically as very ir- 

 regular surfaces with numerous uneven projections into the wall of 

 the cavity. This bizarre resorption was first described by Rowland 

 et al. ( 1959 ) in microradiographs of radium-burdened bone, but has 

 since been found in almost every bone disorder involving rapid re- 



