The natural history of vertebral osteoporosis. Is low bone mass an epiphenomenon?

Osteoporotic bone fragility is due not only to decreased bone mass but to inadequate repair of fatigue damage and to trabecular disconnection. The precise roles and relative contributions of these three factors are not known for osteoporosis in general, and certainly not in any individual case. However, it is known that reduced physical activity causes bone loss. It is a virtual certainty, therefore, that, to the extent that the fracture produces disability, osteoporotics lose bone after they first experience a fracture, whatever its antecedent causes. In that sense, some of the bone loss we find in our patients is indeed an epiphenomenon. However, this is not to suggest that reduced bone mass is unimportant. Quite the contrary: prospective studies have clearly established that reduction in bone mass does increase risk of fracture, and hence, when it is consequent upon a fracture, it aggravates the patient's condition. In this way a vicious circle may develop: the pain and fear that follow fracture lead to decreased activity, which leads to bone loss, which can only increase the fragility, and hence predispose to further fracturing, even in cases in which the initial fragility may not have been due to low bone mass. But low bone mass, with its proper fragility, may not be inevitable. That is why pain control and a comprehensive programme of rehabilitation are critically important in the early management of patients with symptomatic vertebral fractures.