4'>*-2 URIST, MACDONALD, MOSS, AND SKOOG 



et al. ( 1962 ) noted that fractures of the hip are not more common 

 in osteoporotics until after 70 years of age, but that intertrochanteric 

 fractures are more typical of osteoporosis than other tvpes. Although 

 the aged are more susceptible to fractures because of the physiologic 

 decline in bone density, it is clear that incidence of fracture increases 

 further in individuals in older age groups with severe osteoporosis. 

 Previously, Buhr and Cooke (1959) attributed fractures of the hip 

 to "senile matrix of old age." Little et al. (1962), however, con- 

 tended that the bone matrix was degraded or defective in severe 

 osteoporotics, as compared with nonosteoporotic individuals of com- 

 parable age. 



Osteoporosis in Experimental Animals 



The discovery of osteoporosis in the White Leghorn hen ( Urist 

 and Deutsch, 1960a) was followed by the realization that the loss 

 of bone mass is a manifestation of cage layer fatigue (CLF) (Urist, 

 1960« ) . Urist ( 1959 ) had previously observed that hypertrophy of 

 the adrenal cortex developed when normal ^^'hite Leghorns were 

 fed a calcium-deficient diet. But the same variety of laving hens 

 with CLF had atrophied adrenal glands, and the relationship of 

 adrenal hypercorticoidism to avian osteoporosis has not been clari- 

 fied. The problem is the same as with osteoporosis in man. Severe 

 osteoporosis was produced in hens by administration of ACTH 

 (Urist and Deutsch, 1960/?) or cortisone (Urist and Deutsch, 1960c). 

 Roosters were highly resistant; caponized birds were susceptible to 

 bone-destructive properties of these agents. The skeleton of the 

 rooster initially possessed a larger mass of bone than that of the capon 

 or hen, and required a longer period and a larger amount of bone 

 resorption to develop the disorder, but other factors may have been 

 involved. It was not possible to deplete the skeleton of the rooster 

 to the extent that occurs in the hen with CLF. 



Taylor et al. (1962), Taylor (1962), and Bell and Siller (1962) 

 corroborated our observation that osteoporosis is the basic lesion in 

 CLF, and proposed that the cause was genetic and the mechanism 

 was hyperactivity of the pituitary. Bell and Siller (1962) described 

 40 cases in Brown Leghorn hens, and noted hyperosteoclasis of 

 cortical bone and atrophy of muscle as well as bone. Birds with 



