RARKFYIN(; DISEASE OF THE SKELETON 4''23 



Plujsiologic Aging of Bone 



Structural physical and chemical alterations occiu- in the human 

 skeleton in the course of chronological or physiologic aging. Sher- 

 man and Selakovitch (1957) noted that osteocytes begin to disap- 

 pear from the outer lamellae of haversian bone during adolescence, 

 and the number of empty lacunae increases after the 3rd decade. 

 These changes were attributed to circulatory insufficiency and physi- 

 ologic necrosis of bone in old age. Atkinson et al. (1962) measured 

 the dry weight and displacement volume of blocks of bone, w/v = D, 

 and described decrease in thickness and density of cortical bone 

 with increasing age in both sexes after 50; the metaphyseal de- 

 creased faster than the diaphyseal cortex. Sissons (1962) noted that 

 in the aged many osteons ceased to grow when they were half 

 closed, and confirmed Amprino and Engstrom's ( 1952 ) observation 

 that the time between osteon formation and completion of minerali- 

 zation increased with aging. In aged individuals the osteon became 

 rapidly mineralized to 90 per cent of the capacity, but a larger pro- 

 portion of the total bone was always less than 100 per cent mineral- 

 ized. It was easy to distinguish the incompletely mineralized old 

 boile from new bone because the osteon in which old bone is found 

 contains a sclerotic inner edge before it is half closed. 



Lindahl and Lindgren ( 1962 ) observed that in 60 subjects be- 

 tween 14 and 91 years of age, the decrease in bone density was 

 parallel in the upper end of the tibia and the vertebral column. 

 Samples of bone were treated with hot water to remove marrow 

 and with xylene to remove fat, and cut into cubes to measure 

 volume of bone tissue; the density of the sample was the weight 

 per unit volume of the cube. Irrespective of age, osteoporosis was 

 present when the density was 0.20 mg per mm^ of spongy bone. 

 These observations confirmed the conclusions of Trotter et al. ( 1960) 

 that bone density diminishes with age. This is a generalized process, 

 but the rate differs in different bones, in males and females, and in 

 the white and Negro races. According to Morgan et al. (1962), the 

 decline was more pronounced between ages 50 and 65 in women, 

 and usually did not occur in men until age 70. In women, the 



