Bone Mass, Bone Loss, and Osteoporosis Prophylaxis

Throughout most of the 20th century, reduced bone mass was central to the definition of osteoporosis. Indeed, the very etymology of the word osteoporosis connotes a reduction in bone mass. At the 1990 Consensus Conference on Osteoporosis, however, the disorder was redefined as a condition of “skeletal fragility due to decreased bone mass and to microarchitectural deterioration of bone tissue, with a consequent increase in risk of fracture” [1]. Reduced bone mass was thereby relegated to the status of a risk factor for fragility.

This redefinition was a conceptually important shift, inasmuch as it placed the emphasis squarely on fragility fractures and facilitated recognition of other predisposing factors and development of a comprehensive approach that encompassed all factors-extraskeletal as well as skeletal-leading to fragility. Although bone mass is certainly the most extensively studied of the fragility factors, low bone mass is not the whole of the osteoporosis story and may not even be its most important component (despite frequent assertions to the contrary). If one could magically normalize bone mass in everyone, would one eliminate osteoporotic fractures? The best answer that can be given today is “no.” There would be fewer such fractures, but there would still be many, especially hip fractures.

It is both sobering and important to realize that even a young normal hip, when struck just so with approximately the force sustained in a fall from standing height, will fracture [2]. Hui and colleagues [3], while showing the expected increase in fracture risk with declining bone mass, also showed that with bone mass held constant, fracture risk increased with age. More to …