The effect of biphosphonate on induced heterotopic bone

HEBP (1-hydroxy, ethylidene-1, 1-biphosphonate) inhibited mineralization and was observed in matrix-induced heterotopic bone in rabbits. In one group of rabbits, HEBP was administered continuously until sacrifice 20 weeks after the operation. Another group of animals received HEBP for the first four weeks only. The effect of HEBP on de novo bone formation was determined by histologic and biochemical analyses. Implant alkaline and acid phosphatase levels and implant calcium and phosphate contents were measured. The implants of HEBP-treated animals showed diminished implant resorption and, at the same time, formation of atypical osteoid tissue. Quantitative measurements revealed a decrease of acid phosphatase activity, whereas implant alkaline phosphatase activity was unaffected. The mineralization, as depicted by the implant calcium and phosphate content, was almost completely inhibited during HEBP-administration. These effects were completely reversible after the withdrawal of the drug. Remineralization began directly after discontinuation, and recovered only 12 weeks later. The results of this study confirm reports that HEBP cannot prevent the formation of heterotopic ossification. The only effect would be a delay of mineralization during its administration.