Structural changes in aging bone: osteopenia in the proximal femurs of female mice.

A computerized image analysis system was used to quantitate age-related changes in the structure of the proximal femur in CW-1 female mice, ranging from 3 to 32 months of age. Morphological findings revealed a progressive thinning of bone trabeculae within the femoral head, accompanied by the development of marrow cavities in the cortical bone of the femoral neck and in the subchondral bone. As a result, the compact bone in senescent mice acquired an appearance similar to trabecular bone. Quantitative image analysis revealed a similarity in the pattern of changes in the three types of bone: cortical, trabecular, and subchondral. Bone density increased from 3 to 12 months of age and subsequently declined. A similar pattern was noted for the changes in the thickness of the cortical and the subchondral bone. Regression analysis revealed that the changes with age fitted a second-order model; thus it was possible to predict the age of maximal values for each parameter. Hence, the age of maximal bone density for cortical, trabecular, and subchondral bone was 12.3, 14.8, and 18.0 months, respectively. The rate of bone loss after 12 months was most prominent for trabecular bone (1.47% per month), so that by 32 months of age its overall mass had declined by 57% in comparison to peak values seen at 12 months of age (p less than 0.001). The density of the subchondral and cortical bones decreased at a slower rate (0.6% to 0.8% per month) and at the age of 32 months their values had decreased by 12% to 18% in comparison to those at 12 months (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)