UPTAKE AND BIODISTRIBUTION OF TECHNETIUM-99M METHYLENE[P-32]DIPHOSPHONATE DURING ENDOSTEAL HEALING AROUND TITANIUM, STAINLESS-STEEL AND HYDROXYAPATITE IMPLANTS IN RAT TIBIAL BONE

Early evaluation of intraosseous implant success and failure is critic al, but, until now, there have been no reliable systems of measurement . The present study assessed whether the use of (99m)technetium methyl ene-[P-32]diphosphonate ((99m)TcMD(32)P), a marker for both bone forma tion and mineralization, can indicate if an implant is bone-bonding or non-bonding. Moreover, this study examined how bone-bonding (titanium and hydroxyapatite) and non-bonding (stainless steel) implants affect ed the normal healing of bone after marrow ablation, as measured by up take of Tc-99m and P-32. Titanium, hydroxyapatite and stainless steel implants were placed in the right tibiae of Sabra strain rats followin g ablation of the marrow, and (99m)TcMD(32)P was injected 18 h before harvest. At 3, 6, 14, 21 and 42 d (and in some experiments, on days 28 and 35) post-injury, the treated and contralateral tibiae were remove d and cleaned of soft tissue. The uptake of Tc-99m and P-32 was measur ed in the whole bone, as well as in its organic and inorganic phases. Effects of the implants were assessed by comparing the treated to the untreated tibia in each rat. The distribution of Tc-99m and P-32 varie d with each implant. After the insertion of titanium, increased Tc-99m uptake was seen in whole bone and in the inorganic and organic phases at days 6-14. P-32 uptake in whole bone and in the inorganic phase in creased only at day 6, and P-32 uptake was decreased in the organic ph ase at that time. In tibiae implanted with hydroxyapatite, Tc-99m and P-32 uptake was seen in the whole bone at days 6 and 14. While Tc-99m uptake was increased in both the organic and inorganic phases, P-32 up take into the organic phase was decreased at both day 6 and day 14. In tibiae implanted with stainless steel, effects were observed only on day 6. The increased Tc-99m uptake in whole bone reflected increases i n both the organic and mineral phases. Increased P-32 uptake was obser ved in whole bone as well, due to an increase in the P-32 uptake in th e mineral phase only; incorporation of P-32 in the organic phase was c omparable to that found in the contralateral limb. The results of this study indicate that implants alter bone healing, as indicated by the uptake of Tc-99m and P-32 in the different bone compartments. Moreover , decreased P-32 uptake by the organic phase in the presence of bone-b onding implants suggests that cleavage of (99m)TcMD(32)P into its tech netium and methylene diphosphonate moieties was inhibited, perhaps as a function of the onset of calcification in the newly synthesized oste oid. The effect of the implants on bone healing was observed on days 6 -14, when active bone formation and mineralization were occurring, sup porting the hypothesis that these materials modulate events associated with initial calcification. Uptake of Tc-99m varies as a function of time, and uptake of P-32 varies with time and distribution in the mine ral or organic phase of bone, suggesting that these parameters may be useful as indicators of bone-bonding.