Remodeling capacity of calcified fibrocartilage of the hip

It is well known that the incidence of hip fractures increases exponentially with age and that hip fractures can be a major cause of morbidity and morality among elderly humans; this has prompted substantial research on hip fractures. The majority of research on hip fractures has focused on morphological changes of the proximal femur with age. Recently calcified fibrocartilage in the proximal femur has been shown to increase in fractional area with age and can ultimately make up to 60% of the fractional area of the cortex. However, the capacity of the tissue to remodel and heal is currently unknown. The purpose of the present study was to determine the remodeling capacity of calcified fibrocartilage on the proximal femur compared to the underlying cortical bone. The remodeling capacity of calcified fibrocartilage and cortical bone was assessed in adult female sheep by means of tetracycline labeling. The number of double and single labels within each tissue type was quantified and analyzed with a paired t-test. The data showed very few labels in the calcified fibrocartilage compared to the cortical bone. This indicated that calcified fibrocartilage lacked a capacity to remodel in a manner similar to bone. The results of this investigation demonstrate that while the underlying cortical bone was actively remodeling, the calcified fibrocartilage appeared to have no remodeling capacity similar to that of cortical bone. (C) 2004 Wiley-Liss, Inc.