Calcium density measurement in histological samples of trabecular bone of normal subjects: relationship with aging

It is well-known that bone volume decreases with age both in normal subjects and particularly in osteoporotic patients. It is not well demonstrated, however, whether bone loss is associated with changes in the composition of bone tissue and especially with altered concentration of mineral elements. To verify whether calcium density changes with aging, autoptic specimens, of iliac crest trabecular bone from 20 normal subjects between 21 and 66 years, 10 males and 10 females were analyzed by using a new method which allows the measurement of calcium density in a non-destructive way, on entire histologic sections of the bone. Bone specimens were embedded in araidite and tissue sections, about 3 microm thick and 4x4 mm size, were mounted onto polyvinyl acetate films and analyzed by PIXE (proton induced X-ray emission) using the CISE setup for calcium content determination. The same bone tissue sections were then mounted on glass slides, stained with the Von Kossa method and the volume of calcified bone was measured with a semiautomatic image analyzer (Videoplan). 3 to 4 sections from each subject were analyzed and the values of calcium concentration were derived in microg/microl. Similar values of calcium density were found in males and females (535.6+77.1 and 539.2+74.1 microg/microl, respectively). No significant correlation between calcium density and age was observed either in all cases (r=0.0925) or in males (r=-0.0687) and in females (r=0.2676) separately. The unchanged calcium density during aging obtained by combining PIXE and histomorphometric techniques demonstrates that the skeletal calcium reduction observed in old age and probably during osteoporosis, is mainly due to the decrease of bone volume.