ABNORMAL BONE MINERALIZATION AFTER FLUORIDE TREATMENT IN OSTEOPOROSIS- A SMALL-ANGLE X-RAY-SCATTERING STUDY

Sodium fluoride treatment of osteoporosis is known to stimulate bone f ormation and to increase bone mass, but recent clinical trials failed to prove its antifracture effectiveness. The formation of bone with ab normal structure and, therefore, increased fragility is discussed as a possible explanation. Until now, however, exact information on the mi neral structure of osteoporotic bone after fluoride treatment has been lacking. Bone biopsies were taken from three patients with postmenopa usal osteoporosis before and after fluoride treatment (60 mg NaF/day f or 1-2 years), from one patient with iatrogenic fluorosis, as well as from three normal controls. The mineral in these samples was investiga ted by a combination of backscattered electron imaging and small-angle x-ray scattering. Depending on the total dose of fluoride, an increas ing amount of new bone is laid down on the surface of preexisting trab eculae. Its mineral structure is identical to that of heavy fluorosis and is characterized by the presence of additional large crystals, pre sumably located outside the collagen fibrils. These large crystals, wh ich are not present in the controls or in osteoporotic bone before flu oride treatment, contribute to increase the mineral density without si gnificantly improving the biomechanical properties of the bone. The po ssible success of fluoride treatment depends not only on the amount of newly formed bone but also on the rate of bone turnover. Indeed, as s oon as significant amounts of fluoride are present, bone turnover lead s to the replacement of old (normal) bone by new (pathologically miner alized) bone. In particular, in the case of high turnover rates we exp ect fluoride therapy even to lead to a deterioration in the overall me chanical stability of the skeleton.