PREVENTION OF ECTOPIC BONE-FORMATION BY LOCAL APPLICATION OF ETHANE-1-HYDROXY-1,1-DIPHOSPHONATE (EHDP) - AN EXPERIMENTAL-STUDY IN RABBITS

This report shows that ectopic bone formation, a serious problem in orthopedic surgery, can be controlled in an animal model by local application of EHDP (disodium-ethane-1-hydroxy-1,1-diphosphonate). Male New Zealand white rabbits were treated with immobilization and intermittent passive manipulation of the right knee. The treatment caused bone formation in the quadriceps muscle, which was visible on radiographs after 3 weeks. In this model, the effect of methacrylate implants containing EHDP was studied. A concentration of 16 g EHDP/100 g methacrylate inhibited bone formation in experimental cortical defects. Standardized implants containing 16 g EHDP/100 g were then surgically attached to the femur, and the ectopic bone formation created by immobilization and intermittent manipulation was compared with that in rabbits treated with implants but without EHDP. It was found that the EHDP implants were capable of preventing major ectopic bone formation in all cases, whereas all rabbits with an implant containing no EHDP had substantial ectopic bone formation at the end of the experiment.