Age trends in remodeling of the femoral midshaft differ between the sexes

Cross-sectional area properties of the femoral midshaft from 203 individuals of known height and weight, 1-97 years of age, from a modern Australian population were quantified using automatic video image analysis. The aim of this study, taking height and weight into account, was to determine whether (a) age trends in remodeling differ between the sexes, (b) men are better able to compensate for bone loss with age, and (c) this protective mechanism is carried through into old age. Our findings indicated that during adulthood there are distinct gender differences in femoral remodeling. From around the third to the seventh decade, men showed a fairly uniform increase in subperiosteal areal polar moment of inertia, and medullary area. Women displayed two distinct phases during this period: relative stability until around the menopause and then a marked increase in all of the above variables. In old age, gender differences diminished, both sexes showing reduced periosteal apposition and increased endosteal resorption. The resultant decline in cortical area of approximately 4% in men and 15% in women from the third to the eighth decade was significant only in women. For a given height, men had larger, stiffer femoral shafts with a greater cortical width and area and maintained this advantage into old age. Diaphyseal bone was not immune from age-related changes affecting other skeletal sites; however, due to compensatory remodeling, which was particularly evident in men, this was not reflected in increased fracture rates.