The effect of ethane-1-hydroxy-1, 1-diphosphonic acid (EHDP) on matrix induced ectopic bone formation

The effect of diphosphonates (EHDP) was studied on induced ectopic osteoneogenesis. Decalcified allogeneic bone matrix was implanted into the lumbar muscles in rabbits for an ectopic osteoinductor. The ectopic new bone formation was studied under continuous EHDP administration and after discontinuation of EHDP. Although there was no inhibitory effect of EHDP on the osteoinduction, the calcification of the new bone and the resorption of the implanted matrix was retarded. The induced "osteoid-like" tissue had an atypical structure with a small number of cells and a deficiency in collagen fiber bundles. There were also large fields of new cartilage formation. Thus remodelling and mineralization were inhibited under the influence of continuous administration of EHDP. After discontinuation of EHDP administration a recovery phase was observed which seemed to lead to the formation of a normal ossicle.