Structural and remodeling indices in the cancellous bone of the proximal femur across adulthood.

Fragility fractures, including fractures of the femoral neck, result from reductions in the amount, quality and architecture of bone. However, investigations of the underlying structural changes that might predispose to fracture have been largely limited to skeletal sites that do not fracture, such as the iliac crest (IC). The aim of this study was to use histomorphometry to map changes in the architecture and the static remodeling indices of cancellous bone, as a function of age and sex, in bone samples taken from the intertrochanteric (IT) region of the proximal femur at routine autopsy (18-88 years of age). Bone samples for histology were processed from 10-mm cubes of IT cancellous bone. Histomorphometry was performed using an ocular-mounted 10 x 10 graticule at a magnification of x100. An age-dependent decrease in trabecular bone volume was observed in both females and males, as expected (r=-0.75 and r=-0.63, p<0.001, respectively). The underlying mechanisms for bone turnover appeared to be different between males and females. Thus, while the static index of bone resorption (ES/BV) was positively age-dependent in males and females (p<0.001, p<0.03, respectively), the index of bone formation (OS/BV) correlated positively with age in the female group only (p<0.001 vs. NS). Perhaps reflecting an increase in bone formation in older females, the OS/ES ratio was greater in older females than younger females or males. Surprisingly, while resorption indices increased in older males compared with their younger counterparts, bone formation indices increased only in the older female cohort. The IT region in the proximal femur is adjacent to the site commonly involved in fragility fracture. With the limitation that these results describe cross-sectional data, they provide useful insights into changes in the cancellous bone structure and at the bone surface of females and males over the age range of 20-90 years, at a clinically relevant skeletal site.